Version abc80115

7 files changed, 2544 insertions, 18 deletions

diff --git a/src/aig/aig/aigUtil.c b/src/aig/aig/aigUtil.c
index 354d94db..f6f34de9 100644
--- a/src/aig/aig/aigUtil.c
+++ b/src/aig/aig/aigUtil.c
@@ -669,6 +669,10 @@ void Aig_ManDumpBlif( Aig_Man_t * p, char * pFileName )
         printf( "Aig_ManDumpBlif(): AIG manager does not have POs.\n" );
         return;
     }
+    // check if constant is used
+    Aig_ManForEachPo( p, pObj, i )
+        if ( Aig_ObjIsConst1(Aig_ObjFanin0(pObj)) )
+            pConst1 = Aig_ManConst1(p);
     // collect nodes in the DFS order
     vNodes = Aig_ManDfs( p );
     // assign IDs to objects
@@ -698,12 +702,14 @@ void Aig_ManDumpBlif( Aig_Man_t * p, char * pFileName )
     // write latches
     if ( Aig_ManRegNum(p) )
     {
-    fprintf( pFile, "\n" );
-    Aig_ManForEachLiLoSeq( p, pObjLi, pObjLo, i )
-        fprintf( pFile, ".latch n%0*d n%0*d 0\n", nDigits, pObjLi->iData, nDigits, pObjLo->iData );
-    fprintf( pFile, "\n" );
+        fprintf( pFile, "\n" );
+        Aig_ManForEachLiLoSeq( p, pObjLi, pObjLo, i )
+            fprintf( pFile, ".latch n%0*d n%0*d 0\n", nDigits, pObjLi->iData, nDigits, pObjLo->iData );
+        fprintf( pFile, "\n" );
     } 
     // write nodes
+    if ( pConst1 )
+        fprintf( pFile, ".names n%0*d\n 1\n", nDigits, pConst1->iData );
     Vec_PtrForEachEntry( vNodes, pObj, i )
     {
         fprintf( pFile, ".names n%0*d n%0*d n%0*d\n", 
@@ -719,11 +725,7 @@ void Aig_ManDumpBlif( Aig_Man_t * p, char * pFileName )
             nDigits, Aig_ObjFanin0(pObj)->iData, 
             nDigits, pObj->iData );
         fprintf( pFile, "%d 1\n", !Aig_ObjFaninC0(pObj) );
-        if ( Aig_ObjIsConst1(Aig_ObjFanin0(pObj)) )
-            pConst1 = Aig_ManConst1(p);
     }
-    if ( pConst1 )
-        fprintf( pFile, ".names n%0*d\n 1\n", nDigits, pConst1->iData );
     fprintf( pFile, ".end\n\n" );
     fclose( pFile );
     Vec_PtrFree( vNodes );
@@ -751,6 +753,10 @@ void Aig_ManDumpVerilog( Aig_Man_t * p, char * pFileName )
         printf( "Aig_ManDumpBlif(): AIG manager does not have POs.\n" );
         return;
     }
+    // check if constant is used
+    Aig_ManForEachPo( p, pObj, i )
+        if ( Aig_ObjIsConst1(Aig_ObjFanin0(pObj)) )
+            pConst1 = Aig_ManConst1(p);
     // collect nodes in the DFS order
     vNodes = Aig_ManDfs( p );
     // assign IDs to objects
@@ -795,7 +801,11 @@ void Aig_ManDumpVerilog( Aig_Man_t * p, char * pFileName )
     // write nodes
     Vec_PtrForEachEntry( vNodes, pObj, i )
         fprintf( pFile, "wire n%0*d;\n", nDigits, pObj->iData );
+    if ( pConst1 )
+        fprintf( pFile, "wire n%0*d;\n", nDigits, pConst1->iData );
     // write nodes
+    if ( pConst1 )
+        fprintf( pFile, "assign n%0*d = 1\'b1;\n", nDigits, pConst1->iData );
     Vec_PtrForEachEntry( vNodes, pObj, i )
     {
         fprintf( pFile, "assign n%0*d = %sn%0*d & %sn%0*d;\n", 
@@ -810,8 +820,6 @@ void Aig_ManDumpVerilog( Aig_Man_t * p, char * pFileName )
         fprintf( pFile, "assign n%0*d = %sn%0*d;\n", 
             nDigits, pObj->iData,
             !Aig_ObjFaninC0(pObj) ? " " : "~", nDigits, Aig_ObjFanin0(pObj)->iData );
-        if ( Aig_ObjIsConst1(Aig_ObjFanin0(pObj)) )
-            pConst1 = Aig_ManConst1(p);
     }
     if ( Aig_ManRegNum(p) )
     {
@@ -820,12 +828,8 @@ void Aig_ManDumpVerilog( Aig_Man_t * p, char * pFileName )
             fprintf( pFile, "assign n%0*d = %sn%0*d;\n", 
                 nDigits, pObjLi->iData,
                 !Aig_ObjFaninC0(pObjLi) ? " " : "~", nDigits, Aig_ObjFanin0(pObjLi)->iData );
-            if ( Aig_ObjIsConst1(Aig_ObjFanin0(pObjLi)) )
-                pConst1 = Aig_ManConst1(p);
         }
     }
-    if ( pConst1 )
-        fprintf( pFile, "assign n%0*d = 1\'b1;\n", nDigits, pConst1->iData );
 
     // write initial state
     if ( Aig_ManRegNum(p) )
diff --git a/src/base/abci/abc.c b/src/base/abci/abc.c
index da07a936..89eb80a6 100644
--- a/src/base/abci/abc.c
+++ b/src/base/abci/abc.c
@@ -166,6 +166,7 @@ static int Abc_CommandSeq            ( Abc_Frame_t * pAbc, int argc, char ** arg
 static int Abc_CommandUnseq          ( Abc_Frame_t * pAbc, int argc, char ** argv );
 static int Abc_CommandRetime         ( Abc_Frame_t * pAbc, int argc, char ** argv );
 static int Abc_CommandDRetime        ( Abc_Frame_t * pAbc, int argc, char ** argv );
+static int Abc_CommandFlowRetime     ( Abc_Frame_t * pAbc, int argc, char ** argv );
 static int Abc_CommandSeqFpga        ( Abc_Frame_t * pAbc, int argc, char ** argv );
 static int Abc_CommandSeqMap         ( Abc_Frame_t * pAbc, int argc, char ** argv );
 static int Abc_CommandSeqSweep       ( Abc_Frame_t * pAbc, int argc, char ** argv );
@@ -339,6 +340,7 @@ void Abc_Init( Abc_Frame_t * pAbc )
 //    Cmd_CommandAdd( pAbc, "Sequential",   "pipe",          Abc_CommandPipe,             1 );
     Cmd_CommandAdd( pAbc, "Sequential",   "retime",        Abc_CommandRetime,           1 );
     Cmd_CommandAdd( pAbc, "Sequential",   "dretime",       Abc_CommandDRetime,          1 );
+    Cmd_CommandAdd( pAbc, "Sequential",   "fretime",       Abc_CommandFlowRetime,       1 );
 //    Cmd_CommandAdd( pAbc, "Sequential",   "sfpga",         Abc_CommandSeqFpga,          1 );
 //    Cmd_CommandAdd( pAbc, "Sequential",   "smap",          Abc_CommandSeqMap,           1 );
     Cmd_CommandAdd( pAbc, "Sequential",   "ssweep",        Abc_CommandSeqSweep,         1 );
@@ -6292,7 +6294,7 @@ usage:
 int Abc_CommandTest( Abc_Frame_t * pAbc, int argc, char ** argv )
 {
     FILE * pOut, * pErr;
-    Abc_Ntk_t * pNtk;//, * pNtkRes;
+    Abc_Ntk_t * pNtk, * pNtkRes;
     int c;
     int fBmc;
     int nFrames;
@@ -6309,7 +6311,7 @@ int Abc_CommandTest( Abc_Frame_t * pAbc, int argc, char ** argv )
     extern Abc_Ntk_t * Abc_NtkDarToCnf( Abc_Ntk_t * pNtk, char * pFileName );
     extern Abc_Ntk_t * Abc_NtkFilter( Abc_Ntk_t * pNtk );
 //    extern Abc_Ntk_t * Abc_NtkDarRetime( Abc_Ntk_t * pNtk, int nStepsMax, int fVerbose );
-    extern Abc_Ntk_t * Abc_NtkPcmTest( Abc_Ntk_t * pNtk, int fVerbose );
+//    extern Abc_Ntk_t * Abc_NtkPcmTest( Abc_Ntk_t * pNtk, int fVerbose );
     extern Abc_NtkDarHaigRecord( Abc_Ntk_t * pNtk );
     extern void Abc_NtkDarTestBlif( char * pFileName );
 
@@ -6471,8 +6473,8 @@ int Abc_CommandTest( Abc_Frame_t * pAbc, int argc, char ** argv )
 
 //    pNtkRes = Abc_NtkDar( pNtk );
 //    pNtkRes = Abc_NtkDarRetime( pNtk, nLevels, 1 );
-//    pNtkRes = Abc_NtkPcmTest( pNtk, fVerbose );
-    pNtkRes = NULL;
+    pNtkRes = Abc_NtkPcmTest( pNtk, fVerbose );
+//    pNtkRes = NULL;
     if ( pNtkRes == NULL )
     {
         fprintf( pErr, "Command has failed.\n" );
@@ -6481,6 +6483,7 @@ int Abc_CommandTest( Abc_Frame_t * pAbc, int argc, char ** argv )
     // replace the current network
     Abc_FrameReplaceCurrentNetwork( pAbc, pNtkRes );
 */
+
 //    Abc_NtkDarHaigRecord( pNtk );
 //    Abc_NtkDarClau( pNtk, nFrames, nLevels, fBmc, fVerbose, fVeryVerbose );
 
@@ -10441,6 +10444,7 @@ int Abc_CommandInit( Abc_Frame_t * pAbc, int argc, char ** argv )
     }
     else if ( fRandom )
     {
+        srand( time(NULL) );
         Abc_NtkForEachLatch( pNtk, pObj, i )
             if ( rand() & 1 )
                 Abc_LatchSetInit1( pObj );
@@ -11068,6 +11072,133 @@ usage:
     fprintf( pErr, "\t-h     : print the command usage\n");
     return 1;
 }
+/**Function*************************************************************
+
+  Synopsis    []
+
+  Description []
+               
+  SideEffects []
+
+  SeeAlso     []
+
+***********************************************************************/
+int Abc_CommandFlowRetime( Abc_Frame_t * pAbc, int argc, char ** argv )
+{
+    FILE * pOut, * pErr;
+    Abc_Ntk_t * pNtk, * pNtkRes;
+    int c, nMaxIters;
+    int fForward;
+    int fBackward;
+    int fVerbose;
+    int fComputeInit;
+    int maxDelay;
+
+    extern Abc_Ntk_t* Abc_FlowRetime_MinReg( Abc_Ntk_t * pNtk, int fVerbose, int fComputeInit,
+                                             int fForward, int fBackward, int nMaxIters,
+                                             int maxDelay);
+
+    pNtk = Abc_FrameReadNtk(pAbc);
+    pOut = Abc_FrameReadOut(pAbc);
+    pErr = Abc_FrameReadErr(pAbc);
+
+    // set defaults
+    fForward  =  0;
+    fBackward =  0;
+    fComputeInit =  1;
+    fVerbose  =  0;
+    nMaxIters = 999;
+    maxDelay  = 0;
+    Extra_UtilGetoptReset();
+    while ( ( c = Extra_UtilGetopt( argc, argv, "MDfbivh" ) ) != EOF )
+    {
+        switch ( c )
+        {
+        case 'M':
+            if ( globalUtilOptind >= argc )
+            {
+                fprintf( pErr, "Command line switch \"-M\" should be followed by a positive integer.\n" );
+                goto usage;
+            }
+            nMaxIters = atoi(argv[globalUtilOptind]);
+            globalUtilOptind++;
+            if ( nMaxIters < 0 ) 
+                goto usage;
+            break;
+        case 'D':
+            if ( globalUtilOptind >= argc )
+            {
+                fprintf( pErr, "Command line switch \"-D\" should be followed by a positive integer.\n" );
+                goto usage;
+            }
+            maxDelay = atoi(argv[globalUtilOptind]);
+            globalUtilOptind++;
+            if ( maxDelay < 0 ) 
+                goto usage;
+            break;
+        case 'f':
+            fForward ^= 1;
+            break;
+        case 'i':
+            fComputeInit ^= 1;
+            break;
+        case 'b':
+            fBackward ^= 1;
+            break;
+        case 'v':
+            fVerbose ^= 1;
+            break;
+        case 'h':
+            goto usage;
+        default:
+            goto usage;
+        }
+    }
+
+    if ( pNtk == NULL )
+    {
+        fprintf( pErr, "Empty network.\n" );
+        return 1;
+    }
+
+    if ( fForward && fBackward )
+    {
+        fprintf( pErr, "Only one switch \"-f\" or \"-b\" can be selected at a time.\n" );
+        return 1;
+    }
+
+    if ( !Abc_NtkLatchNum(pNtk) )
+    {
+        fprintf( pErr, "The network has no latches. Retiming is not performed.\n" );
+        return 0;
+    }
+
+    if ( Abc_NtkGetChoiceNum(pNtk) )
+      {
+        fprintf( pErr, "Retiming with choice nodes is not implemented.\n" );
+        return 0;
+      }
+
+    // perform the retiming
+    pNtkRes = Abc_FlowRetime_MinReg( pNtk, fVerbose, fComputeInit, fForward, fBackward, nMaxIters, maxDelay );
+
+    if (pNtkRes != pNtk)
+      Abc_FrameReplaceCurrentNetwork( pAbc, pNtkRes );
+
+    return 0;
+
+usage:
+    fprintf( pErr, "usage: fretime [-M num] [-D num] [-fbvih]\n" );
+    fprintf( pErr, "\t         retimes the current network using flow-based algorithm\n" );
+    fprintf( pErr, "\t-M num : the maximum number of iterations [default = %d]\n", nMaxIters );
+    fprintf( pErr, "\t-D num : the maximum delay [default = none]\n" );
+    fprintf( pErr, "\t-i     : enables init state computation [default = %s]\n", fComputeInit? "yes": "no" );
+    fprintf( pErr, "\t-f     : enables forward-only retiming  [default = %s]\n", fForward? "yes": "no" );
+    fprintf( pErr, "\t-b     : enables backward-only retiming [default = %s]\n", fBackward? "yes": "no" );
+    fprintf( pErr, "\t-v     : enables verbose output [default = %s]\n", fVerbose? "yes": "no" );
+    fprintf( pErr, "\t-h     : print the command usage\n");
+    return 1;
+}
 
 /**Function*************************************************************
 
diff --git a/src/opt/fret/fretFlow.c b/src/opt/fret/fretFlow.c
new file mode 100644
index 00000000..599aa341
--- /dev/null
+++ b/src/opt/fret/fretFlow.c
@@ -0,0 +1,640 @@
+/**CFile****************************************************************
+
+  FileName    [fretFlow.c]
+
+  SystemName  [ABC: Logic synthesis and verification system.]
+
+  PackageName [Flow-based retiming package.]
+
+  Synopsis    [Max-flow computation.]
+
+  Author      [Aaron Hurst]
+  
+  Affiliation [UC Berkeley]
+
+  Date        [Ver. 1.0. Started - January 1, 2008.]
+
+  Revision    [$Id: fretFlow.c,v 1.00 2008/01/01 00:00:00 ahurst Exp $]
+
+***********************************************************************/
+
+#include "abc.h"
+#include "vec.h"
+#include "fretime.h"
+
+////////////////////////////////////////////////////////////////////////
+///                        DECLARATIONS                              ///
+////////////////////////////////////////////////////////////////////////
+
+static void dfsfast_e_retreat( Abc_Obj_t *pObj );
+static void dfsfast_r_retreat( Abc_Obj_t *pObj );
+
+#define FDIST(xn, xe, yn, ye) (FDATA(xn)->xe##_dist == (FDATA(yn)->ye##_dist + 1))
+
+////////////////////////////////////////////////////////////////////////
+///                     FUNCTION DEFINITIONS                         ///
+////////////////////////////////////////////////////////////////////////
+
+/**Function*************************************************************
+
+  Synopsis    [Fast DFS.]
+
+  Description [Uses sink-distance-histogram heuristic.  May not find all
+               flow paths: this occurs in a small number of cases where
+               the flow predecessor points to a non-adjacent node and
+               the distance ordering is perturbed.]
+               
+  SideEffects []
+
+  SeeAlso     []
+
+***********************************************************************/
+
+void dfsfast_preorder( Abc_Ntk_t *pNtk ) {
+  Abc_Obj_t *pObj, *pNext;
+  Vec_Ptr_t *vTimeIn, *qn = Vec_PtrAlloc(Abc_NtkObjNum(pNtk));
+  Vec_Int_t *qe = Vec_IntAlloc(Abc_NtkObjNum(pNtk));
+  int i, j, d = 0, end;
+  int qpos = 0;
+
+  // create reverse timing edges for backward traversal
+#if !defined(IGNORE_TIMING)
+  if (maxDelayCon)
+    Abc_NtkForEachObj( pNtk, pObj, i ) {
+      Vec_PtrForEachEntry( FTIMEEDGES(pObj), pNext, j ) {
+        vTimeIn = FDATA(pNext)->vTimeInEdges;
+        if (!vTimeIn) {
+          vTimeIn = FDATA(pNext)->vTimeInEdges = Vec_PtrAlloc(2);
+        }
+        Vec_PtrPush(vTimeIn, pObj);
+      }
+    }
+#endif
+
+  // clear histogram
+  memset(Vec_IntArray(vSinkDistHist), 0, sizeof(int)*Vec_IntSize(vSinkDistHist));
+
+  // seed queue : latches, PIOs, and blocks
+  Abc_NtkForEachObj( pNtk, pObj, i )
+    if (Abc_ObjIsPo(pObj) ||
+        Abc_ObjIsLatch(pObj) || 
+        (fIsForward && FTEST(pObj, BLOCK))) {
+      Vec_PtrPush(qn, pObj);
+      Vec_IntPush(qe, 'r');
+      FDATA(pObj)->r_dist = 1;
+    } else if (Abc_ObjIsPi(pObj) || 
+               (!fIsForward && FTEST(pObj, BLOCK))) {
+      Vec_PtrPush(qn, pObj);
+      Vec_IntPush(qe, 'e');
+      FDATA(pObj)->e_dist = 1;
+    }
+
+  // until queue is empty...
+  while(qpos < Vec_PtrSize(qn)) {
+    pObj = (Abc_Obj_t *)Vec_PtrEntry(qn, qpos);
+    assert(pObj);
+    end = Vec_IntEntry(qe, qpos);
+    qpos++;
+    
+    if (end == 'r') {
+      d = FDATA(pObj)->r_dist;
+
+      // 1. structural edges
+      if (fIsForward) {
+        Abc_ObjForEachFanin( pObj, pNext, i )
+          if (!FDATA(pNext)->e_dist) {
+            FDATA(pNext)->e_dist = d+1;
+            Vec_PtrPush(qn, pNext);
+            Vec_IntPush(qe, 'e');
+          }
+      } else
+        Abc_ObjForEachFanout( pObj, pNext, i )
+          if (!FDATA(pNext)->e_dist) {
+            FDATA(pNext)->e_dist = d+1;
+            Vec_PtrPush(qn, pNext);
+            Vec_IntPush(qe, 'e');
+          }
+
+      if (d == 1) continue;
+
+      // 2. reverse edges (forward retiming only)
+      if (fIsForward) {
+        Abc_ObjForEachFanout( pObj, pNext, i )
+          if (!FDATA(pNext)->r_dist && !Abc_ObjIsLatch(pNext)) {
+            FDATA(pNext)->r_dist = d+1;
+            Vec_PtrPush(qn, pNext);
+            Vec_IntPush(qe, 'r');
+          }          
+      }
+
+      // 3. timimg edges (reverse)
+#if !defined(IGNORE_TIMING)
+      if (maxDelayCon && FDATA(pObj)->vTimeInEdges)
+        Vec_PtrForEachEntry( FDATA(pObj)->vTimeInEdges, pNext, i ) {
+          if (!FDATA(pNext)->r_dist) {
+            FDATA(pNext)->r_dist = d+1;
+            Vec_PtrPush(qn, pNext);
+            Vec_IntPush(qe, 'r');
+          }
+        }
+#endif
+      
+    } else { // if 'e'
+      if (Abc_ObjIsLatch(pObj)) continue;
+
+      d = FDATA(pObj)->e_dist;
+
+      // 1. through node
+      if (!FDATA(pObj)->r_dist) {
+        FDATA(pObj)->r_dist = d+1;
+        Vec_PtrPush(qn, pObj);
+        Vec_IntPush(qe, 'r');
+      }
+
+      // 2. reverse edges (backward retiming only)
+      if (!fIsForward) {
+        Abc_ObjForEachFanin( pObj, pNext, i )
+          if (!FDATA(pNext)->e_dist && !Abc_ObjIsLatch(pNext)) {
+            FDATA(pNext)->e_dist = d+1;
+            Vec_PtrPush(qn, pNext);
+            Vec_IntPush(qe, 'e');
+          }  
+      }
+    }
+  }
+ 
+  // create reverse timing edges for backward traversal
+#if !defined(IGNORE_TIMING)
+  if (maxDelayCon)
+    Abc_NtkForEachObj( pNtk, pObj, i ) {
+      vTimeIn = FDATA(pObj)->vTimeInEdges;
+      if (vTimeIn) {
+        Vec_PtrFree(vTimeIn);
+        FDATA(pObj)->vTimeInEdges = 0;
+      }
+    }
+#endif
+
+  Abc_NtkForEachObj( pNtk, pObj, i ) {
+    Vec_IntAddToEntry(vSinkDistHist, FDATA(pObj)->r_dist, 1);
+    Vec_IntAddToEntry(vSinkDistHist, FDATA(pObj)->e_dist, 1);
+
+#ifdef DEBUG_PREORDER
+    printf("node %d\t: r=%d\te=%d\n", Abc_ObjId(pObj), FDATA(pObj)->r_dist, FDATA(pObj)->e_dist);
+#endif
+  }
+
+  printf("\t\tpre-ordered (max depth=%d)\n", d+1);
+
+  // deallocate
+  Vec_PtrFree( qn );
+  Vec_IntFree( qe );
+}
+
+int dfsfast_e( Abc_Obj_t *pObj, Abc_Obj_t *pPred ) {
+  int i;
+  Abc_Obj_t *pNext;
+  
+  if (fSinkDistTerminate) return 0;
+
+  if(FTEST(pObj, BLOCK) ||
+     Abc_ObjIsPi(pObj)) {
+    assert(!fIsForward);
+    return 1;
+  }
+
+  FSET(pObj, VISITED_E);
+
+#ifdef DEBUG_VISITED
+  printf("(%de=%d) ", Abc_ObjId(pObj), FDATA(pObj)->e_dist);
+#endif  
+
+  // 1. structural edges
+  if (fIsForward)
+    Abc_ObjForEachFanout( pObj, pNext, i ) {
+      if (!FTEST(pNext, VISITED_R) &&
+          FDIST(pObj, e, pNext, r) &&
+          dfsfast_r(pNext, pPred)) {
+#ifdef DEBUG_PRINT_FLOWS
+        printf("o");
+#endif
+        goto found;
+      }
+    }
+  else
+    Abc_ObjForEachFanin( pObj, pNext, i ) {
+      if (!FTEST(pNext, VISITED_R) &&
+          FDIST(pObj, e, pNext, r) &&
+          dfsfast_r(pNext, pPred)) {
+#ifdef DEBUG_PRINT_FLOWS
+        printf("o");
+#endif
+        goto found;
+      }
+    }  
+  
+  if (Abc_ObjIsLatch(pObj))
+    goto not_found;
+
+  // 2. reverse edges (backward retiming only)
+  if (!fIsForward) { 
+    Abc_ObjForEachFanout( pObj, pNext, i ) {
+      if (!FTEST(pNext, VISITED_E) &&
+          FDIST(pObj, e, pNext, e) &&
+          dfsfast_e(pNext, pPred)) {
+#ifdef DEBUG_PRINT_FLOWS
+        printf("i");
+#endif
+        goto found;
+      }
+    }
+  }
+  
+  // unwind
+  if (FTEST(pObj, FLOW) && 
+      !FTEST(pObj, VISITED_R) &&
+      FDIST(pObj, e, pObj, r) &&
+      dfsfast_r(pObj, FGETPRED(pObj))) {
+
+    FUNSET(pObj, FLOW);
+    FSETPRED(pObj, NULL);
+#ifdef DEBUG_PRINT_FLOWS
+    printf("u");
+#endif
+    goto found;
+  }
+  
+ not_found:
+  FUNSET(pObj, VISITED_E);
+  dfsfast_e_retreat(pObj);
+  return 0;
+  
+ found:
+#ifdef DEBUG_PRINT_FLOWS
+  printf("%d ", Abc_ObjId(pObj));
+#endif 
+  FUNSET(pObj, VISITED_E);
+  return 1;
+}
+
+int dfsfast_r( Abc_Obj_t *pObj, Abc_Obj_t *pPred ) {
+  int i;
+  Abc_Obj_t *pNext, *pOldPred;
+
+  if (fSinkDistTerminate) return 0;
+
+#ifdef DEBUG_VISITED
+  printf("(%dr=%d) ", Abc_ObjId(pObj), FDATA(pObj)->r_dist);
+#endif  
+
+  // have we reached the sink?
+  if (Abc_ObjIsLatch(pObj) ||
+      Abc_ObjIsPo(pObj) || 
+      (fIsForward && FTEST(pObj, BLOCK))) {
+    assert(pPred);
+    return 1;
+  }
+
+  FSET(pObj, VISITED_R);
+
+  if (FTEST(pObj, FLOW)) {
+
+    pOldPred = FGETPRED(pObj);
+    if (pOldPred && 
+        !FTEST(pOldPred, VISITED_E) &&
+        FDIST(pObj, r, pOldPred, e) &&
+        dfsfast_e(pOldPred, pOldPred)) {
+
+      FSETPRED(pObj, pPred);
+
+#ifdef DEBUG_PRINT_FLOWS
+      printf("fr");
+#endif
+      goto found;
+    }
+    
+  } else {
+
+    if (!FTEST(pObj, VISITED_E) &&
+        FDIST(pObj, r, pObj, e) &&
+        dfsfast_e(pObj, pObj)) {
+
+      FSET(pObj, FLOW);
+      FSETPRED(pObj, pPred);
+
+#ifdef DEBUG_PRINT_FLOWS
+      printf("f");
+#endif
+      goto found;
+    }
+  }
+ 
+  // 2. reverse edges (forward retiming only)
+  if (fIsForward) {
+    Abc_ObjForEachFanin( pObj, pNext, i ) {
+      if (!FTEST(pNext, VISITED_R) &&
+          FDIST(pObj, r, pNext, r) &&
+          !Abc_ObjIsLatch(pNext) &&
+          dfsfast_r(pNext, pPred)) {
+#ifdef DEBUG_PRINT_FLOWS
+        printf("i");
+#endif
+        goto found;
+      }
+    }
+  }
+  
+  // 3. timing edges
+#if !defined(IGNORE_TIMING)
+  if (maxDelayCon) 
+    Vec_PtrForEachEntry( FTIMEEDGES(pObj), pNext, i) {
+      if (!FTEST(pNext, VISITED_R) &&
+          FDIST(pObj, r, pNext, r) &&
+          dfsfast_r(pNext, pPred)) {
+#ifdef DEBUG_PRINT_FLOWS
+        printf("o");
+#endif
+        goto found;
+      }
+    }
+#endif
+  
+  FUNSET(pObj, VISITED_R);
+  dfsfast_r_retreat(pObj);
+  return 0;
+
+ found:
+#ifdef DEBUG_PRINT_FLOWS
+  printf("%d ", Abc_ObjId(pObj));
+#endif
+  FUNSET(pObj, VISITED_R);
+  return 1;
+}
+
+void
+dfsfast_e_retreat(Abc_Obj_t *pObj) {
+  Abc_Obj_t *pNext;
+  int i, *h;
+  int old_dist = FDATA(pObj)->e_dist;
+  int adj_dist, min_dist = MAX_DIST;
+  
+  // 1. structural edges
+  if (fIsForward)
+    Abc_ObjForEachFanout( pObj, pNext, i ) {
+      adj_dist = FDATA(pNext)->r_dist;
+      if (adj_dist) min_dist = MIN(min_dist, adj_dist);
+    }
+  else
+    Abc_ObjForEachFanin( pObj, pNext, i ) {
+      adj_dist = FDATA(pNext)->r_dist;
+      if (adj_dist) min_dist = MIN(min_dist, adj_dist);
+    }
+
+  if (Abc_ObjIsLatch(pObj)) goto update;
+
+  // 2. through
+  if (FTEST(pObj, FLOW)) {
+    adj_dist = FDATA(pObj)->r_dist;
+    if (adj_dist) min_dist = MIN(min_dist, adj_dist);
+  }
+
+  // 3. reverse edges (backward retiming only)
+  if (!fIsForward) {
+    Abc_ObjForEachFanout( pObj, pNext, i ) {
+      adj_dist = FDATA(pNext)->e_dist;
+      if (adj_dist) min_dist = MIN(min_dist, adj_dist);
+    }
+  }
+
+ update:
+  ++min_dist;
+  if (min_dist >= MAX_DIST) min_dist = 0;
+  // printf("[%de=%d->%d] ", Abc_ObjId(pObj), old_dist, min_dist+1);
+  FDATA(pObj)->e_dist = min_dist;
+
+  assert(min_dist < Vec_IntSize(vSinkDistHist));
+  h = Vec_IntArray(vSinkDistHist);
+  h[old_dist]--;
+  h[min_dist]++;
+  if (!h[old_dist]) {
+    fSinkDistTerminate = 1;
+  }
+}
+
+void
+dfsfast_r_retreat(Abc_Obj_t *pObj) {
+  Abc_Obj_t *pNext;
+  int i, *h;
+  int old_dist = FDATA(pObj)->r_dist;
+  int adj_dist, min_dist = MAX_DIST;
+  
+  // 1. through or pred
+  if (FTEST(pObj, FLOW)) {
+    if (FGETPRED(pObj)) {
+      adj_dist = FDATA(FGETPRED(pObj))->e_dist;
+      if (adj_dist) min_dist = MIN(min_dist, adj_dist);
+    }
+  } else {
+    adj_dist = FDATA(pObj)->e_dist;
+    if (adj_dist) min_dist = MIN(min_dist, adj_dist);
+  }
+
+  // 2. reverse edges (forward retiming only)
+  if (fIsForward) {
+    Abc_ObjForEachFanin( pObj, pNext, i )
+      if (!Abc_ObjIsLatch(pNext)) {
+        adj_dist = FDATA(pNext)->r_dist;
+        if (adj_dist) min_dist = MIN(min_dist, adj_dist);
+      }
+  }
+
+  // 3. timing edges
+#if !defined(IGNORE_TIMING)
+  if (maxDelayCon) 
+    Vec_PtrForEachEntry( FTIMEEDGES(pObj), pNext, i) {
+      adj_dist = FDATA(pNext)->r_dist;
+      if (adj_dist) min_dist = MIN(min_dist, adj_dist);
+    }
+#endif
+
+  ++min_dist;
+  if (min_dist >= MAX_DIST) min_dist = 0;
+  //printf("[%dr=%d->%d] ", Abc_ObjId(pObj), old_dist, min_dist+1);
+  FDATA(pObj)->r_dist = min_dist;
+
+  assert(min_dist < Vec_IntSize(vSinkDistHist));
+  h = Vec_IntArray(vSinkDistHist);
+  h[old_dist]--;
+  h[min_dist]++;
+  if (!h[old_dist]) {
+    fSinkDistTerminate = 1;
+  }
+}
+
+/**Function*************************************************************
+
+  Synopsis    [Plain DFS.]
+
+  Description [Does not use sink-distance-histogram heuristic.]
+               
+  SideEffects []
+
+  SeeAlso     []
+
+***********************************************************************/
+
+int dfsplain_e( Abc_Obj_t *pObj, Abc_Obj_t *pPred ) {
+  int i;
+  Abc_Obj_t *pNext;
+  
+  if (FTEST(pObj, BLOCK) || Abc_ObjIsPi(pObj)) {
+    assert(!fIsForward);
+    return 1;
+  }
+
+  FSET(pObj, VISITED_E);
+  
+  // printf(" %de\n", Abc_ObjId(pObj));
+  
+  // 1. structural edges
+  if (fIsForward)
+    Abc_ObjForEachFanout( pObj, pNext, i ) {
+      if (!FTEST(pNext, VISITED_R) &&
+          dfsplain_r(pNext, pPred)) {
+#ifdef DEBUG_PRINT_FLOWS
+        printf("o");
+#endif
+        goto found;
+      }
+    }
+  else
+    Abc_ObjForEachFanin( pObj, pNext, i ) {
+      if (!FTEST(pNext, VISITED_R) &&
+          dfsplain_r(pNext, pPred)) {
+#ifdef DEBUG_PRINT_FLOWS
+        printf("o");
+#endif
+        goto found;
+      }
+    }
+  
+  if (Abc_ObjIsLatch(pObj))
+    return 0;
+
+  // 2. follow reverse edges
+  if (!fIsForward) { // reverse retiming only
+    Abc_ObjForEachFanout( pObj, pNext, i ) {
+      if (!FTEST(pNext, VISITED_E) &&
+          dfsplain_e(pNext, pPred)) {
+#ifdef DEBUG_PRINT_FLOWS
+        printf("i");
+#endif
+        goto found;
+      }
+    }
+  }
+  
+  // unwind
+  if (FTEST(pObj, FLOW) && 
+      !FTEST(pObj, VISITED_R) &&
+      dfsplain_r(pObj, FGETPRED(pObj))) {
+    FUNSET(pObj, FLOW);
+    FSETPRED(pObj, NULL);
+#ifdef DEBUG_PRINT_FLOWS
+    printf("u");
+#endif
+    goto found;
+  }
+  
+  return 0;
+  
+ found:
+#ifdef DEBUG_PRINT_FLOWS
+  printf("%d ", Abc_ObjId(pObj));
+#endif
+
+  return 1;
+}
+
+int dfsplain_r( Abc_Obj_t *pObj, Abc_Obj_t *pPred ) {
+  int i;
+  Abc_Obj_t *pNext, *pOldPred;
+
+  // have we reached the sink?
+  if (Abc_ObjIsLatch(pObj) || 
+      Abc_ObjIsPo(pObj) || 
+      (fIsForward && FTEST(pObj, BLOCK))) {
+    assert(pPred);
+    return 1;
+  }
+
+  FSET(pObj, VISITED_R);
+
+  // printf(" %dr\n", Abc_ObjId(pObj));
+
+  if (FTEST(pObj, FLOW)) {
+
+    pOldPred = FGETPRED(pObj);
+    if (pOldPred && 
+        !FTEST(pOldPred, VISITED_E) &&
+        dfsplain_e(pOldPred, pOldPred)) {
+
+      FSETPRED(pObj, pPred);
+
+#ifdef DEBUG_PRINT_FLOWS
+      printf("fr");
+#endif
+      goto found;
+    }
+    
+  } else {
+
+    if (!FTEST(pObj, VISITED_E) &&
+        dfsplain_e(pObj, pObj)) {
+
+      FSET(pObj, FLOW);
+      FSETPRED(pObj, pPred);
+
+#ifdef DEBUG_PRINT_FLOWS
+      printf("f");
+#endif
+      goto found;
+    }
+  }
+ 
+  // 2. follow reverse edges
+  if (fIsForward) { // forward retiming only
+    Abc_ObjForEachFanin( pObj, pNext, i ) {
+      if (!FTEST(pNext, VISITED_R) &&
+          !Abc_ObjIsLatch(pNext) &&
+          dfsplain_r(pNext, pPred)) {
+#ifdef DEBUG_PRINT_FLOWS
+        printf("i");
+#endif
+        goto found;
+      }
+    }
+  }
+  
+  // 3. follow timing constraints
+#if !defined(IGNORE_TIMING)
+  if (maxDelayCon) 
+    Vec_PtrForEachEntry( FTIMEEDGES(pObj), pNext, i) {
+      if (!FTEST(pNext, VISITED_R) &&
+          dfsplain_r(pNext, pPred)) {
+#ifdef DEBUG_PRINT_FLOWS
+        printf("o");
+#endif
+        goto found;
+      }
+    }
+#endif
+  
+  return 0;
+
+ found:
+#ifdef DEBUG_PRINT_FLOWS
+  printf("%d ", Abc_ObjId(pObj));
+#endif
+  return 1;
+}
diff --git a/src/opt/fret/fretInit.c b/src/opt/fret/fretInit.c
new file mode 100644
index 00000000..30d1c553
--- /dev/null
+++ b/src/opt/fret/fretInit.c
@@ -0,0 +1,743 @@
+/**CFile****************************************************************
+
+  FileName    [fretInit.c]
+
+  SystemName  [ABC: Logic synthesis and verification system.]
+
+  PackageName [Flow-based retiming package.]
+
+  Synopsis    [Initialization for retiming package.]
+
+  Author      [Aaron Hurst]
+  
+  Affiliation [UC Berkeley]
+
+  Date        [Ver. 1.0. Started - January 1, 2008.]
+
+  Revision    [$Id: fretInit.c,v 1.00 2008/01/01 00:00:00 ahurst Exp $]
+
+***********************************************************************/
+
+#include "abc.h"
+#include "vec.h"
+#include "io.h"
+#include "fretime.h"
+
+////////////////////////////////////////////////////////////////////////
+///                     FUNCTION PROTOTYPES                          ///
+////////////////////////////////////////////////////////////////////////
+
+static void Abc_FlowRetime_UpdateForwardInit_rec( Abc_Obj_t * pObj );
+static void Abc_FlowRetime_VerifyBackwardInit( Abc_Ntk_t * pNtk );
+static void Abc_FlowRetime_VerifyBackwardInit_rec( Abc_Obj_t * pObj );
+static Abc_Obj_t* Abc_FlowRetime_UpdateBackwardInit_rec( Abc_Obj_t *pOrigObj, 
+                                                         Abc_Obj_t *pUseThisPi, Vec_Ptr_t *vOtherPis, 
+                                                         int recurse);
+static void Abc_FlowRetime_SimulateNode( Abc_Obj_t * pObj );
+static void Abc_FlowRetime_SimulateSop( Abc_Obj_t * pObj, char *pSop );
+
+Abc_Ntk_t *pInitNtk;
+int        fSolutionIsDc;
+
+extern void * Abc_FrameReadLibGen();                    
+extern Abc_Ntk_t * Abc_NtkRestrash( Abc_Ntk_t * pNtk, bool fCleanup );
+
+
+////////////////////////////////////////////////////////////////////////
+///                     FUNCTION DEFINITIONS                         ///
+////////////////////////////////////////////////////////////////////////
+
+/**Function*************************************************************
+
+  Synopsis    [Updates initial state information.]
+
+  Description [Assumes latch boxes in original position, latches in
+               new positions.]
+               
+  SideEffects []
+
+  SeeAlso     []
+
+***********************************************************************/
+void
+Abc_FlowRetime_InitState( Abc_Ntk_t * pNtk ) {
+
+  if (!fComputeInitState) return;
+
+  if (fIsForward)
+    Abc_FlowRetime_UpdateForwardInit( pNtk );
+  else {
+    Abc_FlowRetime_UpdateBackwardInit( pNtk );
+  }
+}
+
+
+/**Function*************************************************************
+
+  Synopsis    [Prints initial state information.]
+
+  Description [Prints distribution of 0,1,and X initial states.]
+               
+  SideEffects []
+
+  SeeAlso     []
+
+***********************************************************************/
+void
+Abc_FlowRetime_PrintInitStateInfo( Abc_Ntk_t * pNtk ) {
+  int i, n0=0, n1=0, nDC=0, nOther=0;
+  Abc_Obj_t *pLatch;
+
+  Abc_NtkForEachLatch( pNtk, pLatch, i ) {
+    if (Abc_LatchIsInit0(pLatch)) n0++;
+    else if (Abc_LatchIsInit1(pLatch)) n1++;
+    else if (Abc_LatchIsInitDc(pLatch)) nDC++;
+    else nOther++;
+  }     
+
+  printf("\tinitial states {0,1,x} = {%d, %d, %d}", n0, n1, nDC);
+  if (nOther)
+    printf(" + %d UNKNOWN", nOther);
+  printf("\n");
+}
+
+
+/**Function*************************************************************
+
+  Synopsis    [Computes initial state after forward retiming.]
+
+  Description [Assumes box outputs in old positions stored w/ init values.
+               Uses three-value simulation to preserve don't cares.]
+               
+  SideEffects []
+
+  SeeAlso     []
+
+***********************************************************************/
+void Abc_FlowRetime_UpdateForwardInit( Abc_Ntk_t * pNtk ) {
+  Abc_Obj_t *pObj, *pFanin;
+  int i;
+
+  printf("\t\tupdating init state\n");
+
+  Abc_NtkIncrementTravId( pNtk );
+
+  Abc_NtkForEachLatch( pNtk, pObj, i ) {
+    pFanin = Abc_ObjFanin0(pObj);
+    Abc_FlowRetime_UpdateForwardInit_rec( pFanin );
+
+    if (FTEST(pFanin, INIT_0))
+      Abc_LatchSetInit0( pObj );
+    else if (FTEST(pFanin, INIT_1))
+      Abc_LatchSetInit1( pObj );
+    else
+      Abc_LatchSetInitDc( pObj );
+  }
+}
+
+void Abc_FlowRetime_UpdateForwardInit_rec( Abc_Obj_t * pObj ) {
+  Abc_Obj_t *pNext;
+  int i;
+
+  assert(!Abc_ObjIsPi(pObj)); // should never reach the inputs
+
+  if (Abc_ObjIsBo(pObj)) return;
+
+  // visited?
+  if (Abc_NodeIsTravIdCurrent(pObj)) return;
+  Abc_NodeSetTravIdCurrent(pObj);
+
+  Abc_ObjForEachFanin( pObj, pNext, i ) {
+    Abc_FlowRetime_UpdateForwardInit_rec( pNext );
+  }
+  
+  Abc_FlowRetime_SimulateNode( pObj );
+}
+
+
+/**Function*************************************************************
+
+  Synopsis    [Sets initial value flags.]
+
+  Description []
+               
+  SideEffects []
+
+  SeeAlso     []
+
+***********************************************************************/
+static inline void Abc_FlowRetime_SetInitValue( Abc_Obj_t * pObj,
+                                                int val, int dc ) {
+  
+  // store init value
+  FUNSET(pObj, INIT_CARE);
+  if (!dc){
+    if (val) {
+      FSET(pObj, INIT_1);
+    } else {
+      FSET(pObj, INIT_0);
+    }
+  }
+}
+
+
+/**Function*************************************************************
+
+  Synopsis    [Propogates initial state through a logic node.]
+
+  Description []
+               
+  SideEffects []
+
+  SeeAlso     []
+
+***********************************************************************/
+void Abc_FlowRetime_SimulateNode( Abc_Obj_t * pObj ) {
+  Abc_Ntk_t *pNtk = Abc_ObjNtk(pObj);
+  Abc_Obj_t * pFanin;
+  int i, j, rAnd, rOr, rVar, dcAnd, dcOr, dcVar, v;
+  DdManager * dd = pNtk->pManFunc;
+  DdNode *pBdd = pObj->pData, *pVar;
+  
+  assert(!Abc_ObjIsLatch(pObj));
+
+  // (i) constant nodes
+  if (Abc_NtkHasAig(pNtk) && Abc_AigNodeIsConst(pObj)) {
+    Abc_FlowRetime_SetInitValue(pObj, 1, 0);
+    return;
+  }
+  if (!Abc_NtkIsStrash( pNtk ))
+    if (Abc_NodeIsConst0(pObj)) {
+      Abc_FlowRetime_SetInitValue(pObj, 0, 0);
+      return;
+    } else if (Abc_NodeIsConst1(pObj)) {
+      Abc_FlowRetime_SetInitValue(pObj, 1, 0);
+      return;
+    }
+  
+  // (ii) terminal nodes
+  if (!Abc_ObjIsNode(pObj)) {
+    pFanin = Abc_ObjFanin0(pObj);
+    
+    Abc_FlowRetime_SetInitValue(pObj, 
+         (FTEST(pFanin, INIT_1) ? 1 : 0) ^ pObj->fCompl0, 
+         !FTEST(pFanin, INIT_CARE));    
+    return;
+  }
+
+  // (iii) logic nodes
+
+  // ------ SOP network
+  if ( Abc_NtkHasSop( pNtk )) {
+    Abc_FlowRetime_SimulateSop( pObj, Abc_ObjData(pObj) );
+    return;
+  }
+
+  // ------ BDD network
+  else if ( Abc_NtkHasBdd( pNtk )) {
+    assert(dd);
+    assert(pBdd);
+
+    // cofactor for 0,1 inputs
+    // do nothing for X values
+    Abc_ObjForEachFanin(pObj, pFanin, i) {
+      pVar = Cudd_bddIthVar( dd, i );
+      if (FTEST(pFanin, INIT_CARE))
+        if (FTEST(pFanin, INIT_0)) {
+          pBdd = Cudd_Cofactor( dd, pBdd, Cudd_Not(pVar) ); 
+        } else {
+          pBdd = Cudd_Cofactor( dd, pBdd, pVar ); 
+        }
+    }
+
+    // if function has not been reduced to 
+    // a constant, propagate an X
+    rVar = (pBdd == Cudd_ReadOne(dd));
+    dcVar = !Cudd_IsConstant(pBdd);
+    
+    Abc_FlowRetime_SetInitValue(pObj, rVar, dcVar);
+    return;
+  }
+
+  // ------ AIG network
+  else if ( Abc_NtkHasAig( pNtk )) {
+
+    assert(Abc_AigNodeIsAnd(pObj));
+    dcAnd = 0, rAnd = 1;
+    
+    pFanin = Abc_ObjFanin0(pObj);
+    dcAnd |= FTEST(pFanin, INIT_CARE) ? 0 : 1;
+    rVar = FTEST(pFanin, INIT_0) ? 0 : 1;
+    if (pObj->fCompl0) rVar ^= 1; // complimented?
+    rAnd &= rVar;
+    
+    pFanin = Abc_ObjFanin1(pObj);
+    dcAnd |= FTEST(pFanin, INIT_CARE) ? 0 : 1;
+    rVar = FTEST(pFanin, INIT_0) ? 0 : 1;
+    if (pObj->fCompl1) rVar ^= 1; // complimented?
+    rAnd &= rVar;
+    
+    if (!rAnd) dcAnd = 0; /* controlling value */
+    
+    Abc_FlowRetime_SetInitValue(pObj, rAnd, dcAnd);
+    return;
+  }
+
+  // ------ MAPPED network
+  else if ( Abc_NtkHasMapping( pNtk )) {
+    Abc_FlowRetime_SimulateSop( pObj, Mio_GateReadSop(pObj->pData) );
+    return;
+  }
+
+  assert(0);
+}
+
+
+/**Function*************************************************************
+
+  Synopsis    [Propogates initial state through a SOP node.]
+
+  Description []
+               
+  SideEffects []
+
+  SeeAlso     []
+
+***********************************************************************/
+void Abc_FlowRetime_SimulateSop( Abc_Obj_t * pObj, char *pSop ) {
+  Abc_Obj_t * pFanin;
+  char *pCube;
+  int i, j, rAnd, rOr, rVar, dcAnd, dcOr, dcVar, v;
+
+  assert( pSop && !Abc_SopIsExorType(pSop) );
+      
+  rOr = 0, dcOr = 0;
+
+  i = Abc_SopGetVarNum(pSop);
+  Abc_SopForEachCube( pSop, i, pCube ) {
+    rAnd = 1, dcAnd = 0;
+    Abc_CubeForEachVar( pCube, v, j ) {
+      pFanin = Abc_ObjFanin(pObj, j);
+      if ( v == '0' )
+        rVar = FTEST(pFanin, INIT_0) ? 1 : 0;
+      else if ( v == '1' )
+        rVar = FTEST(pFanin, INIT_1) ? 1 : 0;
+      else
+        continue;
+      
+      if (FTEST(pFanin, INIT_CARE))
+        rAnd &= rVar;
+      else
+        dcAnd = 1;
+    }
+    if (!rAnd) dcAnd = 0; /* controlling value */
+    if (dcAnd) 
+      dcOr = 1;
+    else
+      rOr |= rAnd;
+  }
+  if (rOr) dcOr = 0; /* controlling value */
+  
+  // complement the result if necessary
+  if ( !Abc_SopGetPhase(pSop) )
+    rOr ^= 1;
+      
+  Abc_FlowRetime_SetInitValue(pObj, rOr, dcOr);
+}
+
+/**Function*************************************************************
+
+  Synopsis    [Sets up backward initial state computation.]
+
+  Description []
+               
+  SideEffects []
+
+  SeeAlso     []
+
+***********************************************************************/
+void Abc_FlowRetime_SetupBackwardInit( Abc_Ntk_t * pNtk ) {
+  Abc_Obj_t *pLatch, *pObj, *pPi;
+  int i;
+  Vec_Ptr_t *vObj = Vec_PtrAlloc(100);
+
+  // create the network used for the initial state computation
+  if (Abc_NtkHasMapping(pNtk))
+    pInitNtk = Abc_NtkAlloc( pNtk->ntkType, ABC_FUNC_SOP, 1 );
+  else
+    pInitNtk = Abc_NtkAlloc( pNtk->ntkType, pNtk->ntkFunc, 1 );
+
+  // mitre inputs
+  Abc_NtkForEachLatch( pNtk, pLatch, i ) {
+    // map latch to initial state network
+    pPi = Abc_NtkCreatePi( pInitNtk );
+
+    // has initial state requirement?
+    if (Abc_LatchIsInit0(pLatch)) {
+      
+      if (Abc_NtkHasAig(pNtk))
+        pObj = Abc_ObjNot( pPi );
+      else
+        pObj = Abc_NtkCreateNodeInv( pInitNtk, pPi );
+
+      Vec_PtrPush(vObj, pObj);
+    }
+    else if (Abc_LatchIsInit1(pLatch)) {
+      Vec_PtrPush(vObj, pPi);
+    }
+    
+    Abc_ObjSetData( pLatch, pPi );     // if not verifying init state
+    // FDATA(pLatch)->pInitObj = pPi;  // if verifying init state
+  }
+
+  // are there any nodes not DC?
+  if (!Vec_PtrSize(vObj)) {
+    fSolutionIsDc = 1;
+    return;
+  } else 
+    fSolutionIsDc = 0;
+
+  // mitre output
+  if (Abc_NtkHasAig(pNtk)) {
+    // create AND-by-AND
+    pObj = Vec_PtrPop( vObj );
+    while( Vec_PtrSize(vObj) )
+      pObj = Abc_AigAnd( pInitNtk->pManFunc, pObj, Vec_PtrPop( vObj ) ); 
+  } else
+    // create n-input AND gate
+    pObj = Abc_NtkCreateNodeAnd( pInitNtk, vObj );
+
+  Abc_ObjAddFanin( Abc_NtkCreatePo( pInitNtk ), pObj );
+}
+
+
+/**Function*************************************************************
+
+  Synopsis    [Solves backward initial state computation.]
+
+  Description []
+               
+  SideEffects []
+
+  SeeAlso     []
+
+***********************************************************************/
+void Abc_FlowRetime_SolveBackwardInit( Abc_Ntk_t * pNtk ) {
+  int i;
+  Abc_Obj_t *pObj, *pInitObj;
+  Abc_Ntk_t *pRestrNtk;
+  Vec_Ptr_t *vDelete = Vec_PtrAlloc(0);
+  int result;
+
+  assert(pInitNtk);
+
+  // is the solution entirely DC's?
+  if (fSolutionIsDc) {
+    Abc_NtkDelete(pInitNtk);
+    Vec_PtrFree(vDelete);
+    Abc_NtkForEachLatch( pNtk, pObj, i ) Abc_LatchSetInitDc( pObj );
+    printf("\tno init state computation: all-don't-care solution\n");
+    return;
+  }
+
+  // check that network is combinational
+  // mark superfluous BI nodes for deletion
+  Abc_NtkForEachObj( pInitNtk, pObj, i ) {
+    assert(!Abc_ObjIsLatch(pObj));
+    assert(!Abc_ObjIsBo(pObj));
+    
+    if (Abc_ObjIsBi(pObj)) {
+      Abc_ObjBetterTransferFanout( pObj, Abc_ObjFanin0(pObj), Abc_ObjFaninC0(pObj) );
+      Vec_PtrPush( vDelete, pObj );
+    }
+  }
+  
+  // delete superfluous nodes
+  while(Vec_PtrSize( vDelete )) {
+    pObj = (Abc_Obj_t *)Vec_PtrPop( vDelete );
+    Abc_NtkDeleteObj( pObj );
+  }
+  Vec_PtrFree(vDelete);
+
+  // do some final cleanup on the network
+  Abc_NtkAddDummyPoNames(pInitNtk);
+  Abc_NtkAddDummyPiNames(pInitNtk);
+  if (Abc_NtkIsLogic(pInitNtk))
+    Abc_NtkCleanup(pInitNtk, 0);
+  else if (Abc_NtkIsStrash(pInitNtk)) {  
+    Abc_NtkReassignIds(pInitNtk);
+  }
+  
+  printf("\tsolving for init state (%d nodes)... ", Abc_NtkObjNum(pInitNtk));
+  fflush(stdout);
+
+  // convert SOPs to BDD
+  if (Abc_NtkHasSop(pInitNtk))
+    Abc_NtkSopToBdd( pInitNtk );
+  
+  // solve
+  result = Abc_NtkMiterSat( pInitNtk, (sint64)500000, (sint64)50000000, 0, NULL, NULL );
+
+  if (!result) printf("SUCCESS\n");
+  else  {
+    printf("FAILURE\n");  
+    printf("\tsetting all initial states to don't-care\n");
+    Abc_NtkForEachLatch( pNtk, pObj, i ) Abc_LatchSetInitDc( pObj );
+    return;
+  }
+
+  // clear initial values, associate PIs to latches
+  Abc_NtkForEachPi( pInitNtk, pInitObj, i ) Abc_ObjSetCopy( pInitObj, NULL );
+  Abc_NtkForEachLatch( pNtk, pObj, i ) {
+    pInitObj = Abc_ObjData( pObj );
+    assert( Abc_ObjIsPi( pInitObj ));
+    Abc_ObjSetCopy( pInitObj, pObj );
+    Abc_LatchSetInitNone( pObj );
+  }
+
+  // copy solution from PIs to latches
+  assert(pInitNtk->pModel);
+  Abc_NtkForEachPi( pInitNtk, pInitObj, i ) {
+    if ((pObj = Abc_ObjCopy( pInitObj ))) {
+      if ( pInitNtk->pModel[i] )
+        Abc_LatchSetInit1( pObj );
+      else
+        Abc_LatchSetInit0( pObj );
+    }
+  }
+
+#if defined(DEBUG_CHECK)
+  // check that all latches have initial state
+  Abc_NtkForEachLatch( pNtk, pObj, i ) assert( !Abc_LatchIsInitNone( pObj ) );
+#endif
+
+  // deallocate
+  Abc_NtkDelete( pInitNtk );
+}
+
+
+/**Function*************************************************************
+
+  Synopsis    [Updates backward initial state computation problem.]
+
+  Description [Assumes box outputs in old positions stored w/ init values.]
+               
+  SideEffects []
+
+  SeeAlso     []
+
+***********************************************************************/
+void Abc_FlowRetime_UpdateBackwardInit( Abc_Ntk_t * pNtk ) {
+  Abc_Obj_t *pOrigObj,  *pOrigFanin, *pInitObj, *pInitFanin;
+  Vec_Ptr_t *vBo = Vec_PtrAlloc(100);
+  Vec_Ptr_t *vOldPis = Vec_PtrAlloc(100);
+  void *pData;
+  int i, j;
+
+  // remove PIs from network (from BOs)
+  Abc_NtkForEachObj( pNtk, pOrigObj, i )
+    if (Abc_ObjIsBo(pOrigObj)) {
+      pInitObj = FDATA(pOrigObj)->pInitObj;
+      assert(Abc_ObjIsPi(pInitObj));
+      Vec_PtrPush(vBo, pOrigObj);
+
+      Abc_FlowRetime_UpdateBackwardInit_rec( Abc_ObjFanin0( pOrigObj ), pInitObj, vOldPis, 0 );
+    }
+
+  // add PIs to network (at latches)
+  Abc_NtkForEachLatch( pNtk, pOrigObj, i )
+    Abc_FlowRetime_UpdateBackwardInit_rec( pOrigObj, NULL, vOldPis, 0 );
+  
+  // connect nodes in init state network
+  Vec_PtrForEachEntry( vBo, pOrigObj, i )
+    Abc_FlowRetime_UpdateBackwardInit_rec( Abc_ObjFanin0( pOrigObj ), NULL, NULL, 1 );
+  
+  // clear flags
+  Abc_NtkForEachObj( pNtk, pOrigObj, i )
+    pOrigObj->fMarkA = pOrigObj->fMarkB = 0;
+
+  // deallocate
+  Vec_PtrFree( vBo );
+  Vec_PtrFree( vOldPis );
+}
+
+
+/**Function*************************************************************
+
+  Synopsis    [Updates backward initial state computation problem.]
+
+  Description [Creates a duplicate node in the initial state network 
+               corresponding to a node in the original circuit.  If
+               fRecurse is set, the procedure recurses on and connects
+               the new node to its fan-ins.  A latch in the original
+               circuit corresponds to a PI in the initial state network.
+               An existing PI may be supplied by pUseThisPi, and if the
+               node is a latch, it will be used; otherwise the PI is
+               saved in the list vOtherPis and subsequently used for
+               another latch.]
+               
+  SideEffects [Nodes that have a corresponding initial state node
+               are marked with fMarkA.  Nodes that have been fully
+               connected in the initial state network are marked with
+               fMarkB.]
+
+  SeeAlso     []
+
+***********************************************************************/
+Abc_Obj_t* Abc_FlowRetime_UpdateBackwardInit_rec( Abc_Obj_t *pOrigObj, 
+                                                  Abc_Obj_t *pUseThisPi, Vec_Ptr_t *vOtherPis, 
+                                                  int fRecurse) {
+  Abc_Obj_t *pInitObj, *pOrigFanin, *pInitFanin;
+  void      *pData;
+  int i;
+  Abc_Ntk_t *pNtk = Abc_ObjNtk( pOrigObj );
+
+  // should never reach primary IOs
+  assert(!Abc_ObjIsPi(pOrigObj));
+  assert(!Abc_ObjIsPo(pOrigObj));
+
+  // if fanin is latch, it becomes a primary input
+  if (Abc_ObjIsLatch( pOrigObj )) {
+    if (pOrigObj->fMarkA)  return FDATA(pOrigObj)->pInitObj;
+
+    assert(vOtherPis);
+    
+    if (pUseThisPi) { 
+      // reuse curent PI     
+      pInitObj = pUseThisPi; }
+    else { 
+      // reuse previous PI
+      pInitObj = (Abc_Obj_t*)Vec_PtrPop(vOtherPis); 
+    }
+    
+    // remember link from original node to init ntk
+    Abc_ObjSetData( pOrigObj, pInitObj ); 
+
+    pOrigObj->fMarkA = 1;
+    return (FDATA(pOrigObj)->pInitObj = pInitObj);
+  } 
+
+  // does an init node already exist?
+  if(!pOrigObj->fMarkA) {
+
+    if (Abc_NtkHasMapping( pNtk )) {
+      if (!pOrigObj->pData) {
+        // assume terminal...
+        assert(Abc_ObjFaninNum(pOrigObj) == 1);
+        pInitObj = Abc_NtkCreateNodeBuf( pInitNtk, NULL );
+      } else {
+        pInitObj = Abc_NtkCreateObj( pInitNtk, Abc_ObjType(pOrigObj) );
+        pData = Mio_GateReadSop(pOrigObj->pData);
+        assert( Abc_SopGetVarNum(pData) == Abc_ObjFaninNum(pOrigObj) );
+
+        pInitObj->pData = Abc_SopRegister( pInitNtk->pManFunc, pData );
+      }
+    } else {
+      pData = Abc_ObjCopy( pOrigObj );   // save ptr to flow data    
+      if (Abc_NtkIsStrash( pNtk ) && Abc_AigNodeIsConst( pOrigObj ))
+        pInitObj = Abc_AigConst1( pInitNtk );
+      else
+        pInitObj = Abc_NtkDupObj( pInitNtk, pOrigObj, 0 );
+      Abc_ObjSetCopy( pOrigObj, pData ); // restore ptr to flow data
+
+      // copy complementation
+      pInitObj->fCompl0 = pOrigObj->fCompl0;
+      pInitObj->fCompl1 = pOrigObj->fCompl1;
+      pInitObj->fPhase = pOrigObj->fPhase;
+    }
+
+    // if we didn't use given PI, immediately transfer fanouts
+    // and add to list for later reuse
+    if (pUseThisPi) {
+      Abc_ObjBetterTransferFanout( pUseThisPi, pInitObj, 0 );
+      Vec_PtrPush( vOtherPis, pUseThisPi );
+    }
+
+    pOrigObj->fMarkA = 1;
+    FDATA(pOrigObj)->pInitObj = pInitObj;
+  } else {
+    pInitObj = FDATA(pOrigObj)->pInitObj;
+  }
+    
+  // have we already connected this object?
+  if (fRecurse && !pOrigObj->fMarkB) {
+
+    // create and/or connect fanins
+    Abc_ObjForEachFanin( pOrigObj, pOrigFanin, i ) {
+      pInitFanin = Abc_FlowRetime_UpdateBackwardInit_rec( pOrigFanin, NULL, NULL, fRecurse );
+      Abc_ObjAddFanin( pInitObj, pInitFanin );
+    }
+
+    pOrigObj->fMarkB = 1;
+  }
+
+  return pInitObj;
+}
+
+
+/**Function*************************************************************
+
+  Synopsis    [Verifies backward init state computation.]
+
+  Description [This procedure requires the BOs to store the original
+               latch values and the latches to store the new values:
+               both in the INIT_0 and INIT_1 flags in the Flow_Data
+               structure.  (This is not currently the case in the rest
+               of the code.)  Also, can not verify backward state
+               computations that span multiple combinational frames.]
+               
+  SideEffects []
+
+  SeeAlso     []
+
+***********************************************************************/
+void Abc_FlowRetime_VerifyBackwardInit( Abc_Ntk_t * pNtk ) {
+  Abc_Obj_t *pObj, *pFanin;
+  int i;
+
+  printf("\t\tupdating init state\n");
+
+  Abc_NtkIncrementTravId( pNtk );
+
+  Abc_NtkForEachObj( pNtk, pObj, i )
+    if (Abc_ObjIsBo( pObj )) {
+      pFanin = Abc_ObjFanin0(pObj);
+      Abc_FlowRetime_VerifyBackwardInit_rec( pFanin );
+
+      if (FTEST(pObj, INIT_CARE)) {
+        if(FTEST(pObj, INIT_CARE) != FTEST(pFanin, INIT_CARE)) {
+          printf("ERROR: expected val=%d care=%d and got val=%d care=%d\n",
+                 FTEST(pObj, INIT_1)?1:0, FTEST(pObj, INIT_CARE)?1:0, 
+                 FTEST(pFanin, INIT_1)?1:0, FTEST(pFanin, INIT_CARE)?1:0 );
+
+        }
+      }
+    }
+}
+
+void Abc_FlowRetime_VerifyBackwardInit_rec( Abc_Obj_t * pObj ) {
+  Abc_Obj_t *pNext;
+  int i;
+
+  assert(!Abc_ObjIsBo(pObj)); // should never reach the inputs
+  assert(!Abc_ObjIsPi(pObj)); // should never reach the inputs
+
+  // visited?
+  if (Abc_NodeIsTravIdCurrent(pObj)) return;
+  Abc_NodeSetTravIdCurrent(pObj);
+
+  if (Abc_ObjIsLatch(pObj)) {
+    FUNSET(pObj, INIT_CARE);
+    if (Abc_LatchIsInit0(pObj))
+      FSET(pObj, INIT_0);
+    else if (Abc_LatchIsInit1(pObj))
+      FSET(pObj, INIT_1);
+    return;
+  }
+
+  Abc_ObjForEachFanin( pObj, pNext, i ) {
+    Abc_FlowRetime_VerifyBackwardInit_rec( pNext );
+  }
+  
+  Abc_FlowRetime_SimulateNode( pObj );
+}
diff --git a/src/opt/fret/fretMain.c b/src/opt/fret/fretMain.c
new file mode 100644
index 00000000..4ce78a9b
--- /dev/null
+++ b/src/opt/fret/fretMain.c
@@ -0,0 +1,864 @@
+/**CFile****************************************************************
+
+  FileName    [fretMain.c]
+
+  SystemName  [ABC: Logic synthesis and verification system.]
+
+  PackageName [Flow-based retiming package.]
+
+  Synopsis    [Main file for retiming package.]
+
+  Author      [Aaron Hurst]
+  
+  Affiliation [UC Berkeley]
+
+  Date        [Ver. 1.0. Started - January 1, 2008.]
+
+  Revision    [$Id: fretMain.c,v 1.00 2008/01/01 00:00:00 ahurst Exp $]
+
+***********************************************************************/
+
+#include "abc.h"
+#include "vec.h"
+#include "fretime.h"
+
+////////////////////////////////////////////////////////////////////////
+///                        DECLARATIONS                              ///
+////////////////////////////////////////////////////////////////////////
+
+static void Abc_FlowRetime_AddDummyFanin( Abc_Obj_t * pObj );
+
+static void Abc_FlowRetime_MarkBlocks( Abc_Ntk_t * pNtk );
+static void Abc_FlowRetime_MarkReachable_rec( Abc_Obj_t * pObj, char end );
+static int  Abc_FlowRetime_PushFlows( Abc_Ntk_t * pNtk );
+static int  Abc_FlowRetime_ImplementCut( Abc_Ntk_t * pNtk );
+static void  Abc_FlowRetime_RemoveLatchBubbles( Abc_Obj_t * pLatch );
+
+static void Abc_FlowRetime_VerifyPathLatencies( Abc_Ntk_t * pNtk );
+static int  Abc_FlowRetime_VerifyPathLatencies_rec( Abc_Obj_t * pObj, int markD );
+
+extern void Abc_NtkMarkCone_rec( Abc_Obj_t * pObj, int fForward );
+extern Abc_Ntk_t * Abc_NtkRestrash( Abc_Ntk_t * pNtk, bool fCleanup );
+
+int         fIsForward, fComputeInitState;
+int         fSinkDistTerminate;
+Vec_Int_t  *vSinkDistHist;
+int         maxDelayCon;
+
+int         fPathError = 0;
+
+////////////////////////////////////////////////////////////////////////
+///                     FUNCTION DEFINITIONS                         ///
+////////////////////////////////////////////////////////////////////////
+
+/**Function*************************************************************
+
+  Synopsis    [Performs minimum-register retiming.]
+
+  Description []
+               
+  SideEffects []
+
+  SeeAlso     []
+
+***********************************************************************/
+Abc_Ntk_t *
+Abc_FlowRetime_MinReg( Abc_Ntk_t * pNtk, int fVerbose, int fComputeInitState_,
+                       int fForwardOnly, int fBackwardOnly, int nMaxIters,
+                       int maxDelay ) {
+
+  int i, j, nNodes, nLatches, flow, last, cut;
+  int iteration = 0;
+  Flow_Data_t *pDataArray;
+  Abc_Obj_t   *pObj, *pNext;
+
+  fComputeInitState = fComputeInitState_;
+
+  printf("Flow-based minimum-register retiming...\n");  
+
+  if (!Abc_NtkHasOnlyLatchBoxes(pNtk)) {
+    printf("\tERROR: Can not retime with black/white boxes\n");
+    return pNtk;
+  }
+
+  maxDelayCon = maxDelay;
+  if (maxDelayCon) {
+    printf("\tmax delay constraint = %d\n", maxDelayCon);
+    if (maxDelayCon < (i = Abc_NtkLevel(pNtk))) {
+      printf("ERROR: max delay constraint must be > current max delay (%d)\n", i);
+      return pNtk;
+    }
+  }
+
+  // print info about type of network
+  printf("\tnetlist type = ");
+  if (Abc_NtkIsNetlist( pNtk )) printf("netlist/");
+  else if (Abc_NtkIsLogic( pNtk )) printf("logic/");
+  else if (Abc_NtkIsStrash( pNtk )) printf("strash/");
+  else printf("***unknown***/");
+  if (Abc_NtkHasSop( pNtk )) printf("sop\n");
+  else if (Abc_NtkHasBdd( pNtk )) printf("bdd\n");
+  else if (Abc_NtkHasAig( pNtk )) printf("aig\n");
+  else if (Abc_NtkHasMapping( pNtk )) printf("mapped\n");
+  else printf("***unknown***\n");
+
+  printf("\tinitial reg count = %d\n", Abc_NtkLatchNum(pNtk));
+
+  // remove bubbles from latch boxes
+  Abc_FlowRetime_PrintInitStateInfo(pNtk);
+  printf("\tpushing bubbles out of latch boxes\n");
+  Abc_NtkForEachLatch( pNtk, pObj, i )
+    Abc_FlowRetime_RemoveLatchBubbles(pObj);
+  Abc_FlowRetime_PrintInitStateInfo(pNtk);
+
+  // check for box inputs/outputs
+  Abc_NtkForEachLatch( pNtk, pObj, i ) {
+    assert(Abc_ObjFaninNum(pObj) == 1);
+    assert(Abc_ObjFanoutNum(pObj) == 1);
+    assert(!Abc_ObjFaninC0(pObj));
+
+    pNext = Abc_ObjFanin0(pObj);
+    assert(Abc_ObjIsBi(pNext));
+    assert(Abc_ObjFaninNum(pNext) <= 1);
+    if(Abc_ObjFaninNum(pNext) == 0) // every Bi should have a fanin
+      Abc_FlowRetime_AddDummyFanin( pNext );
+ 
+    pNext = Abc_ObjFanout0(pObj);
+    assert(Abc_ObjIsBo(pNext));
+    assert(Abc_ObjFaninNum(pNext) == 1);
+    assert(!Abc_ObjFaninC0(pNext));
+  }
+
+  nLatches = Abc_NtkLatchNum( pNtk );
+  nNodes = Abc_NtkObjNumMax( pNtk )+1;
+   
+  // build histogram
+  vSinkDistHist = Vec_IntStart( nNodes*2+10 );
+
+  // create Flow_Data structure
+  pDataArray = (Flow_Data_t *)malloc(sizeof(Flow_Data_t)*nNodes);
+  memset(pDataArray, 0, sizeof(Flow_Data_t)*nNodes);
+  Abc_NtkForEachObj( pNtk, pObj, i )
+    Abc_ObjSetCopy( pObj, (void *)(&pDataArray[i]) );
+
+  // (i) forward retiming loop
+  fIsForward = 1;
+
+  if (!fBackwardOnly) do {
+    if (iteration == nMaxIters) break;
+
+    printf("\tforward iteration %d\n", iteration);
+    last = Abc_NtkLatchNum( pNtk );
+
+    Abc_FlowRetime_MarkBlocks( pNtk );
+    flow = Abc_FlowRetime_PushFlows( pNtk );
+    cut = Abc_FlowRetime_ImplementCut( pNtk );
+
+    // clear all
+    memset(pDataArray, 0, sizeof(Flow_Data_t)*nNodes);    
+    iteration++;
+  } while( flow != last );
+
+  // print info about initial states
+  if (fComputeInitState)
+    Abc_FlowRetime_PrintInitStateInfo( pNtk );
+
+  // (ii) backward retiming loop
+  fIsForward = 0;
+  iteration = 0;
+
+  if (!fForwardOnly) {
+    if (fComputeInitState) {
+      Abc_FlowRetime_SetupBackwardInit( pNtk );
+    }
+
+    do {
+      if (iteration == nMaxIters) break;
+
+      printf("\tbackward iteration %d\n", iteration);
+      last = Abc_NtkLatchNum( pNtk );
+      
+      Abc_FlowRetime_MarkBlocks( pNtk );
+      flow = Abc_FlowRetime_PushFlows( pNtk );
+      cut = Abc_FlowRetime_ImplementCut( pNtk );
+      
+      // clear all
+      memset(pDataArray, 0, sizeof(Flow_Data_t)*nNodes);    
+      iteration++;
+
+    } while( flow != last );
+    
+    // compute initial states
+    if (fComputeInitState) {
+      Abc_FlowRetime_SolveBackwardInit( pNtk );
+      Abc_FlowRetime_PrintInitStateInfo( pNtk );
+    }
+  }
+
+  // clear pCopy field
+  Abc_NtkForEachObj( pNtk, pObj, i ) {
+    Abc_ObjSetCopy( pObj, NULL );
+
+    // if not computing init state, set all latches to DC
+    if (!fComputeInitState && Abc_ObjIsLatch(pObj))
+      Abc_LatchSetInitDc(pObj);
+  }
+
+  // restrash if necessary
+  if (Abc_NtkIsStrash(pNtk)) {
+    Abc_NtkReassignIds( pNtk );
+    pNtk = Abc_NtkRestrash( pNtk, 1 );
+  }
+  
+#if defined(DEBUG_CHECK)
+  Abc_NtkDoCheck( pNtk );
+#endif
+
+  // deallocate space
+  free(pDataArray);
+  if (vSinkDistHist) Vec_IntFree(vSinkDistHist);
+
+  printf("\tfinal reg count = %d\n", Abc_NtkLatchNum(pNtk));
+
+  return pNtk;
+}
+
+/**Function*************************************************************
+
+  Synopsis    [Pushes latch bubbles outside of box.]
+
+  Description [If network is an AIG, a fCompl0 is allowed to remain on
+               the BI node.]
+               
+  SideEffects []
+
+  SeeAlso     []
+
+***********************************************************************/
+void
+Abc_FlowRetime_RemoveLatchBubbles( Abc_Obj_t * pLatch ) {
+  int i, j, k, bubble = 0;
+  Abc_Ntk_t *pNtk = Abc_ObjNtk( pLatch );
+  Abc_Obj_t *pBi, *pBo, *pInv;
+      
+  pBi = Abc_ObjFanin0(pLatch);
+  pBo = Abc_ObjFanout0(pLatch);
+  assert(!Abc_ObjIsComplement(pBi));
+  assert(!Abc_ObjIsComplement(pBo));
+
+  // push bubbles on BO into latch box
+  if (Abc_ObjFaninC0(pBo) && Abc_ObjFanoutNum(pBo) > 0) {
+    bubble = 1;
+    if (Abc_LatchIsInit0(pLatch)) Abc_LatchSetInit1(pLatch);
+    else if (Abc_LatchIsInit1(pLatch)) Abc_LatchSetInit0(pLatch);  
+  }
+
+  // absorb bubbles on BI
+  pBi->fCompl0 ^= bubble ^ Abc_ObjFaninC0(pLatch);
+
+  // convert bubble to INV if not AIG
+  if (!Abc_NtkHasAig( pNtk ) && Abc_ObjFaninC0(pBi)) {
+    pBi->fCompl0 = 0;
+    pInv = Abc_NtkCreateNodeInv( pNtk, Abc_ObjFanin0(pBi) );
+    Abc_ObjPatchFanin( pBi, Abc_ObjFanin0(pBi), pInv );
+  }
+
+  pBo->fCompl0 = 0;
+  pLatch->fCompl0 = 0;
+}
+
+
+/**Function*************************************************************
+
+  Synopsis    [Marks nodes in TFO/TFI of PI/PO.]
+
+  Description [Sets flow data flag BLOCK appropriately.]
+               
+  SideEffects []
+
+  SeeAlso     []
+
+***********************************************************************/
+void
+Abc_FlowRetime_MarkBlocks( Abc_Ntk_t * pNtk ) {
+  int i;
+  Abc_Obj_t *pObj;
+
+  if (fIsForward){
+    // mark the frontier
+    Abc_NtkForEachPo( pNtk, pObj, i )
+      pObj->fMarkA = 1;
+    Abc_NtkForEachLatch( pNtk, pObj, i )
+      {
+        pObj->fMarkA = 1;
+      }
+    // mark the nodes reachable from the PIs
+    Abc_NtkForEachPi( pNtk, pObj, i )
+      Abc_NtkMarkCone_rec( pObj, fIsForward );
+  } else {
+    // mark the frontier
+    Abc_NtkForEachPi( pNtk, pObj, i )
+      pObj->fMarkA = 1;
+    Abc_NtkForEachLatch( pNtk, pObj, i )
+      {
+        pObj->fMarkA = 1;
+      }
+    // mark the nodes reachable from the POs
+    Abc_NtkForEachPo( pNtk, pObj, i )
+      Abc_NtkMarkCone_rec( pObj, fIsForward );
+  }
+
+  // copy marks
+  Abc_NtkForEachObj( pNtk, pObj, i ) {
+    if (pObj->fMarkA) {
+      pObj->fMarkA = 0;
+      if (!Abc_ObjIsLatch(pObj) && 
+          !Abc_ObjIsPi(pObj))
+        FSET(pObj, BLOCK);
+    }
+  }
+}
+
+
+/**Function*************************************************************
+
+  Synopsis    [Computes maximum flow.]
+
+  Description []
+               
+  SideEffects [Leaves VISITED flags on source-reachable nodes.]
+
+  SeeAlso     []
+
+***********************************************************************/
+int
+Abc_FlowRetime_PushFlows( Abc_Ntk_t * pNtk ) {
+  int i, j, flow = 0, last, srcDist = 0;
+  Abc_Obj_t   *pObj, *pObj2;
+
+  fSinkDistTerminate = 0;
+  dfsfast_preorder( pNtk );
+
+  // (i) fast max-flow computation
+  while(!fSinkDistTerminate && srcDist < MAX_DIST) {
+    srcDist = MAX_DIST;
+    Abc_NtkForEachLatch( pNtk, pObj, i )
+      if (FDATA(pObj)->e_dist)    
+        srcDist = MIN(srcDist, FDATA(pObj)->e_dist);
+    
+    Abc_NtkForEachLatch( pNtk, pObj, i ) {
+      if (srcDist == FDATA(pObj)->e_dist &&
+          dfsfast_e( pObj, NULL )) {
+#ifdef DEBUG_PRINT_FLOWS
+        printf("\n\n");
+#endif
+        flow++;
+      }
+    }
+  }
+
+  printf("\t\tmax-flow1 = %d \t", flow);
+
+  // (ii) complete max-flow computation
+  // also, marks source-reachable nodes
+  do {
+    last = flow;
+    Abc_NtkForEachLatch( pNtk, pObj, i ) {
+      if (dfsplain_e( pObj, NULL )) {
+#ifdef DEBUG_PRINT_FLOWS
+        printf("\n\n");
+#endif
+        flow++;
+        Abc_NtkForEachObj( pNtk, pObj2, j )
+          FUNSET( pObj2, VISITED );
+      }
+    }
+  } while (flow > last);
+  
+  printf("max-flow2 = %d\n", flow);
+
+  return flow;
+}
+
+
+/**Function*************************************************************
+
+  Synopsis    [Restores latch boxes.]
+
+  Description [Latchless BI/BO nodes are removed.  Latch boxes are 
+               restored around remaining latches.]
+               
+  SideEffects [Deletes nodes as appropriate.]
+
+  SeeAlso     []
+
+***********************************************************************/
+void
+Abc_FlowRetime_FixLatchBoxes( Abc_Ntk_t *pNtk, Vec_Ptr_t *vBoxIns ) {
+  int i;
+  Abc_Obj_t *pObj, *pNext, *pBo = NULL, *pBi = NULL;
+  Vec_Ptr_t *vFreeBi = Vec_PtrAlloc( 100 );
+  Vec_Ptr_t *vFreeBo = Vec_PtrAlloc( 100 );
+  Vec_Ptr_t *vNodes;
+
+  // 1. remove empty bi/bo pairs
+  while(Vec_PtrSize( vBoxIns )) {
+    pBi = (Abc_Obj_t *)Vec_PtrPop( vBoxIns );
+    assert(Abc_ObjIsBi(pBi));
+    assert(Abc_ObjFanoutNum(pBi) == 1);
+    assert(Abc_ObjFaninNum(pBi) == 1);
+    pBo = Abc_ObjFanout0(pBi);
+    assert(!Abc_ObjFaninC0(pBo));
+
+    if (Abc_ObjIsBo(pBo)) {
+      // an empty bi/bo pair
+
+      Abc_ObjRemoveFanins( pBo );
+      // transfer complement from BI, if present 
+      assert(!Abc_ObjIsComplement(Abc_ObjFanin0(pBi)));
+      Abc_ObjBetterTransferFanout( pBo, Abc_ObjFanin0(pBi), Abc_ObjFaninC0(pBi) );
+
+      Abc_ObjRemoveFanins( pBi );
+      pBi->fCompl0 = 0;
+      Vec_PtrPush( vFreeBi, pBi );
+      Vec_PtrPush( vFreeBo, pBo );
+
+      // free names
+      // if (Nm_ManFindNameById(pNtk->pManName, Abc_ObjId(pBi)))
+      //  Nm_ManDeleteIdName( pNtk->pManName, Abc_ObjId(pBi));
+      //if (Nm_ManFindNameById(pNtk->pManName, Abc_ObjId(pBo)))
+      //  Nm_ManDeleteIdName( pNtk->pManName, Abc_ObjId(pBo));
+
+      // check for complete detachment
+      assert(Abc_ObjFaninNum(pBi) == 0);
+      assert(Abc_ObjFanoutNum(pBi) == 0);
+      assert(Abc_ObjFaninNum(pBo) == 0);
+      assert(Abc_ObjFanoutNum(pBo) == 0);
+    } else assert(Abc_ObjIsLatch(pBo));
+  }
+
+  // 2. add bi/bos as necessary for latches
+  Abc_NtkForEachLatch( pNtk, pObj, i ) {
+    assert(Abc_ObjFaninNum(pObj) == 1);
+    if (Abc_ObjFanoutNum(pObj))
+      pBo = Abc_ObjFanout0(pObj);
+    else pBo = NULL;
+    pBi = Abc_ObjFanin0(pObj);
+    
+    // add BO
+    if (!pBo || !Abc_ObjIsBo(pBo)) {
+      pBo = (Abc_Obj_t *)Vec_PtrPop( vFreeBo );
+      if (Abc_ObjFanoutNum(pObj))  Abc_ObjTransferFanout( pObj, pBo );
+      Abc_ObjAddFanin( pBo, pObj );
+    }
+    // add BI
+    if (!Abc_ObjIsBi(pBi)) {
+      pBi = (Abc_Obj_t *)Vec_PtrPop( vFreeBi );
+      assert(Abc_ObjFaninNum(pBi) == 0);
+      Abc_ObjAddFanin( pBi, Abc_ObjFanin0(pObj) );
+      pBi->fCompl0 = pObj->fCompl0;
+      Abc_ObjRemoveFanins( pObj );
+      Abc_ObjAddFanin( pObj, pBi );
+    }
+  }
+
+  // delete remaining BIs and BOs
+  while(Vec_PtrSize( vFreeBi )) {
+    pObj = (Abc_Obj_t *)Vec_PtrPop( vFreeBi );
+    Abc_NtkDeleteObj( pObj );
+  }
+  while(Vec_PtrSize( vFreeBo )) {
+    pObj = (Abc_Obj_t *)Vec_PtrPop( vFreeBo );
+    Abc_NtkDeleteObj( pObj );
+  }
+
+#if defined(DEBUG_CHECK)
+  Abc_NtkForEachObj( pNtk, pObj, i ) {
+    if (Abc_ObjIsBo(pObj)) {
+      assert(Abc_ObjFaninNum(pObj) == 1);
+      assert(Abc_ObjIsLatch(Abc_ObjFanin0(pObj))); 
+    }
+    if (Abc_ObjIsBi(pObj)) {
+      assert(Abc_ObjFaninNum(pObj) == 1);
+      assert(Abc_ObjFanoutNum(pObj) == 1);
+      assert(Abc_ObjIsLatch(Abc_ObjFanout0(pObj))); 
+    }
+    if (Abc_ObjIsLatch(pObj)) {
+      assert(Abc_ObjFanoutNum(pObj) == 1);
+      assert(Abc_ObjFaninNum(pObj) == 1);
+    }
+  }
+#endif
+
+  Vec_PtrFree( vFreeBi );
+  Vec_PtrFree( vFreeBo );
+}
+
+
+/**Function*************************************************************
+
+  Synopsis    [Checks register count along all combinational paths.]
+
+  Description []
+               
+  SideEffects []
+
+  SeeAlso     []
+
+***********************************************************************/
+void
+Abc_FlowRetime_VerifyPathLatencies( Abc_Ntk_t * pNtk ) {
+  int i;
+  Abc_Obj_t *pObj;
+  fPathError = 0;
+
+  printf("\t\tVerifying latency along all paths...");
+
+  Abc_NtkForEachObj( pNtk, pObj, i ) {
+    if (Abc_ObjIsBo(pObj)) {
+      Abc_FlowRetime_VerifyPathLatencies_rec( pObj, 0 );
+    } else if (!fIsForward && Abc_ObjIsPi(pObj)) {
+      Abc_FlowRetime_VerifyPathLatencies_rec( pObj, 0 );
+    }
+
+    if (fPathError) {
+      if (Abc_ObjFaninNum(pObj) > 0) {
+        printf("fanin ");
+        print_node(Abc_ObjFanin0(pObj));
+      }
+      printf("\n");
+      exit(0);
+    }
+  }
+
+  printf(" ok\n");
+
+  Abc_NtkForEachObj( pNtk, pObj, i ) {
+    pObj->fMarkA = 0;
+    pObj->fMarkB = 0;
+    pObj->fMarkC = 0;
+  }
+}
+
+
+int
+Abc_FlowRetime_VerifyPathLatencies_rec( Abc_Obj_t * pObj, int markD ) {
+  int i, j;
+  Abc_Obj_t *pNext;
+  int fCare = 0;
+  int markC = pObj->fMarkC;
+
+  if (!pObj->fMarkB) {
+    pObj->fMarkB = 1; // visited
+    
+    if (Abc_ObjIsLatch(pObj))
+      markC = 1;      // latch in output
+    
+    if (!fIsForward && !Abc_ObjIsPo(pObj) && !Abc_ObjFanoutNum(pObj))
+      return -1; // dangling non-PO outputs : don't care what happens
+    
+    Abc_ObjForEachFanout( pObj, pNext, i ) {
+      // reached end of cycle?
+      if ( Abc_ObjIsBo(pNext) ||
+           (fIsForward && Abc_ObjIsPo(pNext)) ) {
+        if (!markD && !Abc_ObjIsLatch(pObj)) {
+          printf("\nERROR: no-latch path (end)\n");
+          print_node(pNext);
+          printf("\n");
+          fPathError = 1;
+        }
+      } else if (!fIsForward && Abc_ObjIsPo(pNext)) {
+        if (markD || Abc_ObjIsLatch(pObj)) {
+          printf("\nERROR: extra-latch path to outputs\n");
+          print_node(pNext);
+          printf("\n");
+          fPathError = 1;
+        }
+      } else {
+        j = Abc_FlowRetime_VerifyPathLatencies_rec( pNext, markD || Abc_ObjIsLatch(pObj) );
+        if (j >= 0) {
+          markC |= j;
+          fCare = 1;
+        }
+      }
+
+      if (fPathError) {
+        print_node(pObj);
+        printf("\n");
+        return 0;
+      }
+    }
+  }
+
+  if (!fCare) return -1;
+
+  if (markC && markD) {
+    printf("\nERROR: mult-latch path\n");
+    print_node(pObj);
+    printf("\n");
+    fPathError = 1;
+  }
+  if (!markC && !markD) {
+    printf("\nERROR: no-latch path (inter)\n");
+    print_node(pObj);
+    printf("\n");
+    fPathError = 1;
+  }
+
+  return (pObj->fMarkC = markC);
+}
+
+
+/**Function*************************************************************
+
+  Synopsis    [Copies initial state from latches to BO nodes.]
+
+  Description [Initial states are marked on BO nodes with INIT_0 and
+               INIT_1 flags in their Flow_Data structures.]
+               
+  SideEffects []
+
+  SeeAlso     []
+
+***********************************************************************/
+void
+Abc_FlowRetime_CopyInitState( Abc_Obj_t * pSrc, Abc_Obj_t * pDest ) {
+  Abc_Obj_t *pObj;
+
+  if (!fComputeInitState) return;
+
+  assert(Abc_ObjIsLatch(pSrc));
+  assert(Abc_ObjFanin0(pDest) == pSrc);
+  assert(!Abc_ObjFaninC0(pDest));
+
+  FUNSET(pDest, INIT_CARE);
+  if (Abc_LatchIsInit0(pSrc)) {
+    FSET(pDest, INIT_0);
+  } else if (Abc_LatchIsInit1(pSrc)) {
+    FSET(pDest, INIT_1);  
+  }
+  
+  if (!fIsForward) {
+    pObj = Abc_ObjData(pSrc);
+    assert(Abc_ObjIsPi(pObj));
+    FDATA(pDest)->pInitObj = pObj;
+  }
+}
+
+
+/**Function*************************************************************
+
+  Synopsis    [Implements min-cut.]
+
+  Description [Requires source-reachable nodes to be marked VISITED.]
+               
+  SideEffects []
+
+  SeeAlso     []
+
+***********************************************************************/
+int
+Abc_FlowRetime_ImplementCut( Abc_Ntk_t * pNtk ) {
+  int i, j, cut = 0, unmoved = 0;
+  Abc_Obj_t *pObj, *pReg, *pNext, *pBo = NULL, *pBi = NULL;
+  Vec_Ptr_t *vFreeRegs = Vec_PtrAlloc( Abc_NtkLatchNum(pNtk) );
+  Vec_Ptr_t *vBoxIns = Vec_PtrAlloc( Abc_NtkLatchNum(pNtk) );
+  Vec_Ptr_t *vMove = Vec_PtrAlloc( 100 );
+
+  // remove latches from netlist
+  Abc_NtkForEachLatch( pNtk, pObj, i ) {
+    pBo = Abc_ObjFanout0(pObj);
+    pBi = Abc_ObjFanin0(pObj);
+    assert(Abc_ObjIsBo(pBo) && Abc_ObjIsBi(pBi));
+    Vec_PtrPush( vBoxIns, pBi );
+
+    // copy initial state values to BO
+    Abc_FlowRetime_CopyInitState( pObj, pBo );
+
+    // re-use latch elsewhere
+    Vec_PtrPush( vFreeRegs, pObj );
+    FSET(pBo, CROSS_BOUNDARY);
+
+    // cut out of netlist
+    Abc_ObjPatchFanin( pBo, pObj, pBi );
+    Abc_ObjRemoveFanins( pObj );
+
+    // free name
+    // if (Nm_ManFindNameById(pNtk->pManName, Abc_ObjId(pObj)))
+    //  Nm_ManDeleteIdName( pNtk->pManName, Abc_ObjId(pObj));
+  }
+
+  // insert latches into netlist
+  Abc_NtkForEachObj( pNtk, pObj, i ) {
+    if (Abc_ObjIsLatch( pObj )) continue;
+    
+    // a latch is required on every node that lies across the min-cit
+    assert(!fIsForward || !FTEST(pObj, VISITED_E) || FTEST(pObj, VISITED_R));
+    if (FTEST(pObj, VISITED_R) && !FTEST(pObj, VISITED_E)) {
+      assert(FTEST(pObj, FLOW));
+
+      // count size of cut
+      cut++;
+      if ((fIsForward && Abc_ObjIsBo(pObj)) || 
+          (!fIsForward && Abc_ObjIsBi(pObj)))
+        unmoved++;
+      
+      // only insert latch between fanouts that lie across min-cut
+      // some fanout paths may be cut at deeper points
+      Abc_ObjForEachFanout( pObj, pNext, j )
+        if (fIsForward) {
+          if (!FTEST(pNext, VISITED_R) || 
+              FTEST(pNext, BLOCK) || 
+              FTEST(pNext, CROSS_BOUNDARY) || 
+              Abc_ObjIsLatch(pNext))
+            Vec_PtrPush(vMove, pNext);
+        } else {
+          if (FTEST(pNext, VISITED_E) ||
+              FTEST(pNext, CROSS_BOUNDARY))
+            Vec_PtrPush(vMove, pNext);
+        }
+      if (Vec_PtrSize(vMove) == 0)
+        print_node(pObj);
+
+      assert(Vec_PtrSize(vMove) > 0);
+      
+      // insert one of re-useable registers
+      assert(Vec_PtrSize( vFreeRegs ));
+      pReg = (Abc_Obj_t *)Vec_PtrPop( vFreeRegs );
+      
+      Abc_ObjAddFanin(pReg, pObj);
+      while(Vec_PtrSize( vMove )) {
+        pNext = (Abc_Obj_t *)Vec_PtrPop( vMove );
+        Abc_ObjPatchFanin( pNext, pObj, pReg );
+        if (Abc_ObjIsBi(pNext)) assert(Abc_ObjFaninNum(pNext) == 1);
+
+      }
+      if (Abc_ObjIsBi(pObj)) assert(Abc_ObjFaninNum(pObj) == 1);
+    }
+  }
+
+#if defined(DEBUG_CHECK)        
+  Abc_FlowRetime_VerifyPathLatencies( pNtk );
+#endif
+
+  // delete remaining latches
+  while(Vec_PtrSize( vFreeRegs )) {
+    pReg = (Abc_Obj_t *)Vec_PtrPop( vFreeRegs );
+    Abc_NtkDeleteObj( pReg );
+  }
+  
+  // update initial states
+  Abc_FlowRetime_InitState( pNtk );
+
+  // restore latch boxes
+  Abc_FlowRetime_FixLatchBoxes( pNtk, vBoxIns );
+
+  Vec_PtrFree( vFreeRegs );
+  Vec_PtrFree( vMove );
+  Vec_PtrFree( vBoxIns );
+
+  printf("\t\tmin-cut = %d (unmoved = %d)\n", cut, unmoved);
+  return cut;
+}
+
+/**Function*************************************************************
+
+  Synopsis    [Adds dummy fanin.]
+
+  Description []
+               
+  SideEffects []
+
+  SeeAlso     []
+
+***********************************************************************/
+void
+Abc_FlowRetime_AddDummyFanin( Abc_Obj_t * pObj ) {
+  Abc_Ntk_t *pNtk = Abc_ObjNtk( pObj );
+
+  if (Abc_NtkHasAig(pNtk)) 
+    Abc_ObjAddFanin(pObj, Abc_AigConst1( pNtk ));
+  else
+    Abc_ObjAddFanin(pObj, Abc_NtkCreateNodeConst0( pNtk ));
+}
+
+
+/**Function*************************************************************
+
+  Synopsis    [Prints information about a node.]
+
+  Description [Debuging.]
+               
+  SideEffects []
+
+  SeeAlso     []
+
+***********************************************************************/
+void
+print_node(Abc_Obj_t *pObj) {
+  int i;
+  Abc_Obj_t * pNext;
+  char m[6];
+
+  m[0] = 0;
+  if (pObj->fMarkA)
+    strcat(m, "A");
+  if (pObj->fMarkB)
+    strcat(m, "B");
+  if (pObj->fMarkC)
+    strcat(m, "C");
+
+  printf("node %d type=%d (%x%s) fanouts {", Abc_ObjId(pObj), Abc_ObjType(pObj), FDATA(pObj)->mark, m);
+  Abc_ObjForEachFanout( pObj, pNext, i )
+    printf("%d (%d),", Abc_ObjId(pNext), FDATA(pNext)->mark);
+  printf("} fanins {");
+  Abc_ObjForEachFanin( pObj, pNext, i )
+    printf("%d (%d),", Abc_ObjId(pNext), FDATA(pNext)->mark);
+  printf("} ");
+}
+
+void
+print_node2(Abc_Obj_t *pObj) {
+  int i;
+  Abc_Obj_t * pNext;
+  char m[6];
+
+  m[0] = 0;
+  if (pObj->fMarkA)
+    strcat(m, "A");
+  if (pObj->fMarkB)
+    strcat(m, "B");
+  if (pObj->fMarkC)
+    strcat(m, "C");
+
+  printf("node %d type=%d fanouts {", Abc_ObjId(pObj), Abc_ObjType(pObj), m);
+  Abc_ObjForEachFanout( pObj, pNext, i )
+    printf("%d ,", Abc_ObjId(pNext));
+  printf("} fanins {");
+  Abc_ObjForEachFanin( pObj, pNext, i )
+    printf("%d ,", Abc_ObjId(pNext));
+  printf("} ");
+}
+
+
+/**Function*************************************************************
+
+  Synopsis    [Transfers fanout.]
+
+  Description [Does not produce an error if there is no fanout.
+               Complements as necessary.]
+               
+  SideEffects []
+
+  SeeAlso     []
+
+***********************************************************************/
+void 
+Abc_ObjBetterTransferFanout( Abc_Obj_t * pFrom, Abc_Obj_t * pTo, int compl ) {
+  Abc_Obj_t *pNext;
+  
+  while(Abc_ObjFanoutNum(pFrom) > 0) {
+    pNext = Abc_ObjFanout0(pFrom);
+    Abc_ObjPatchFanin( pNext, pFrom, Abc_ObjNotCond(pTo, compl) );
+  }
+}
diff --git a/src/opt/fret/fretime.h b/src/opt/fret/fretime.h
new file mode 100644
index 00000000..f12bd30b
--- /dev/null
+++ b/src/opt/fret/fretime.h
@@ -0,0 +1,140 @@
+/**CFile****************************************************************
+
+  FileName    [fretime.h]
+
+  SystemName  [ABC: Logic synthesis and verification system.]
+
+  PackageName [Flow-based retiming package.]
+
+  Synopsis    [Header file for retiming package.]
+
+  Author      [Aaron Hurst]
+  
+  Affiliation [UC Berkeley]
+
+  Date        [Ver. 1.0. Started - January 1, 2008.]
+
+  Revision    [$Id: fretime.h,v 1.00 2008/01/01 00:00:00 ahurst Exp $]
+
+***********************************************************************/
+
+#if !defined(RETIME_H_)
+#define RETIME_H_
+
+#include "abc.h"
+
+#define IGNORE_TIMING
+// #define DEBUG_PRINT_FLOWS
+// #define DEBUG_VISITED
+// #define DEBUG_PREORDER
+// #define DEBUG_CHECK
+
+////////////////////////////////////////////////////////////////////////
+///                        DECLARATIONS                              ///
+////////////////////////////////////////////////////////////////////////
+
+#define MAX_DIST 30000
+
+// flags in Flow_Data structure...
+#define VISITED_E       0x01
+#define VISITED_R       0x02
+#define VISITED  (VISITED_E | VISITED_R)
+#define FLOW            0x04
+#define CROSS_BOUNDARY  0x08
+#define BLOCK           0x10
+#define INIT_0          0x20
+#define INIT_1          0x40
+#define INIT_CARE (INIT_0 | INIT_1)
+
+typedef struct Untimed_Flow_Data_t_ {
+  unsigned int mark : 8;
+
+  union {
+    Abc_Obj_t   *pred;
+    /* unsigned int var; */
+    Abc_Obj_t   *pInitObj;
+  };
+
+  unsigned int e_dist : 16;
+  unsigned int r_dist : 16;
+} Untimed_Flow_Data_t;
+
+typedef struct Timed_Flow_Data_t_ {
+  unsigned int mark : 8;
+
+  union {
+    Abc_Obj_t   *pred;
+    Vec_Ptr_t   *vTimeInEdges;
+    /* unsigned int var; */
+    Abc_Obj_t   *pInitObj;
+  };
+
+  unsigned int e_dist : 16;
+  unsigned int r_dist : 16;
+
+  Vec_Ptr_t    vTimeEdges;
+
+} Timed_Flow_Data_t;
+
+#if defined(IGNORE_TIMING)
+typedef Untimed_Flow_Data_t Flow_Data_t;
+#else
+typedef Timed_Flow_Data_t Flow_Data_t;
+#endif
+
+// useful macros for manipulating Flow_Data structure...
+#define FDATA( x )     ((Flow_Data_t *)Abc_ObjCopy(x))
+#define FSET( x, y )   ((Flow_Data_t *)Abc_ObjCopy(x))->mark |= y
+#define FUNSET( x, y ) ((Flow_Data_t *)Abc_ObjCopy(x))->mark &= ~y
+#define FTEST( x, y )  (((Flow_Data_t *)Abc_ObjCopy(x))->mark & y)
+#define FTIMEEDGES( x )  &(((Timed_Flow_Data_t *)Abc_ObjCopy(x))->vTimeEdges)
+
+static inline void FSETPRED(Abc_Obj_t *pObj, Abc_Obj_t *pPred) {
+  assert(!Abc_ObjIsLatch(pObj)); // must preserve field to maintain init state linkage
+  FDATA(pObj)->pred = pPred;
+}
+static inline Abc_Obj_t * FGETPRED(Abc_Obj_t *pObj) {
+  return FDATA(pObj)->pred;
+}
+
+/*=== fretMain.c ==========================================================*/
+
+Abc_Ntk_t *    Abc_FlowRetime_MinReg( Abc_Ntk_t * pNtk, int fVerbose, int fComputeInitState,
+                                      int fForward, int fBackward, int nMaxIters,
+                                      int maxDelay);
+
+void print_node(Abc_Obj_t *pObj);
+
+void Abc_ObjBetterTransferFanout( Abc_Obj_t * pFrom, Abc_Obj_t * pTo, int compl );
+
+extern int         fIsForward;
+extern int         fSinkDistTerminate;
+extern Vec_Int_t  *vSinkDistHist;
+extern int         maxDelayCon;
+extern int         fComputeInitState;
+
+/*=== fretFlow.c ==========================================================*/
+
+int  dfsplain_e( Abc_Obj_t *pObj, Abc_Obj_t *pPred );
+int  dfsplain_r( Abc_Obj_t *pObj, Abc_Obj_t *pPred );
+
+void dfsfast_preorder( Abc_Ntk_t *pNtk );
+int  dfsfast_e( Abc_Obj_t *pObj, Abc_Obj_t *pPred );
+int  dfsfast_r( Abc_Obj_t *pObj, Abc_Obj_t *pPred );
+
+/*=== fretInit.c ==========================================================*/
+
+void Abc_FlowRetime_PrintInitStateInfo( Abc_Ntk_t * pNtk );
+
+void Abc_FlowRetime_InitState( Abc_Ntk_t * pNtk );
+
+void Abc_FlowRetime_UpdateForwardInit( Abc_Ntk_t * pNtk );
+void Abc_FlowRetime_UpdateBackwardInit( Abc_Ntk_t * pNtk );
+
+void Abc_FlowRetime_SetupBackwardInit( Abc_Ntk_t * pNtk );
+void Abc_FlowRetime_SolveBackwardInit( Abc_Ntk_t * pNtk );
+
+extern Abc_Ntk_t *pInitNtk;
+extern int        fSolutionIsDc;
+
+#endif
diff --git a/src/opt/fret/module.make b/src/opt/fret/module.make
new file mode 100644
index 00000000..72fdfec9
--- /dev/null
+++ b/src/opt/fret/module.make
@@ -0,0 +1,4 @@
+SRC +=    src/opt/fret/fretMain.c \
+    src/opt/fret/fretFlow.c \
+        src/opt/fret/fretInit.c
+