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-rw-r--r--backends/simplec/.gitignore2
-rw-r--r--backends/simplec/Makefile.inc3
-rw-r--r--backends/simplec/simplec.cc521
-rw-r--r--backends/simplec/test00.sh5
-rw-r--r--backends/simplec/test00_tb.c78
-rw-r--r--backends/simplec/test00_uut.v14
6 files changed, 623 insertions, 0 deletions
diff --git a/backends/simplec/.gitignore b/backends/simplec/.gitignore
new file mode 100644
index 000000000..f08796168
--- /dev/null
+++ b/backends/simplec/.gitignore
@@ -0,0 +1,2 @@
+test00_tb
+test00_uut.c
diff --git a/backends/simplec/Makefile.inc b/backends/simplec/Makefile.inc
new file mode 100644
index 000000000..fee1376c5
--- /dev/null
+++ b/backends/simplec/Makefile.inc
@@ -0,0 +1,3 @@
+
+OBJS += backends/simplec/simplec.o
+
diff --git a/backends/simplec/simplec.cc b/backends/simplec/simplec.cc
new file mode 100644
index 000000000..3fd28fefe
--- /dev/null
+++ b/backends/simplec/simplec.cc
@@ -0,0 +1,521 @@
+/*
+ * yosys -- Yosys Open SYnthesis Suite
+ *
+ * Copyright (C) 2012 Clifford Wolf <clifford@clifford.at>
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ *
+ */
+
+#include "kernel/yosys.h"
+#include "kernel/sigtools.h"
+
+USING_YOSYS_NAMESPACE
+PRIVATE_NAMESPACE_BEGIN
+
+struct HierDirtyFlags;
+
+struct HierDirtyFlags
+{
+ int dirty;
+ Module *module;
+ IdString hiername;
+ HierDirtyFlags *parent;
+ pool<SigBit> dirty_bits;
+ pool<Cell*> dirty_cells;
+ dict<IdString, HierDirtyFlags*> children;
+
+ HierDirtyFlags(Module *module, IdString hiername, HierDirtyFlags *parent) : dirty(0), module(module), hiername(hiername), parent(parent)
+ {
+ for (Cell *cell : module->cells()) {
+ Module *mod = module->design->module(cell->type);
+ if (mod) children[cell->name] = new HierDirtyFlags(mod, cell->name, this);
+ }
+ }
+
+ ~HierDirtyFlags()
+ {
+ for (auto &child : children)
+ delete child.second;
+ }
+
+ void set_dirty(SigBit bit)
+ {
+ if (dirty_bits.count(bit))
+ return;
+
+ dirty_bits.insert(bit);
+
+ HierDirtyFlags *p = this;
+ while (p != nullptr) {
+ p->dirty++;
+ p = p->parent;
+ }
+ }
+
+ void unset_dirty(SigBit bit)
+ {
+ if (dirty_bits.count(bit) == 0)
+ return;
+
+ dirty_bits.erase(bit);
+
+ HierDirtyFlags *p = this;
+ while (p != nullptr) {
+ p->dirty--;
+ log_assert(p->dirty >= 0);
+ p = p->parent;
+ }
+ }
+
+ void set_dirty(Cell *cell)
+ {
+ if (dirty_cells.count(cell))
+ return;
+
+ dirty_cells.insert(cell);
+
+ HierDirtyFlags *p = this;
+ while (p != nullptr) {
+ p->dirty++;
+ p = p->parent;
+ }
+ }
+
+ void unset_dirty(Cell *cell)
+ {
+ if (dirty_cells.count(cell) == 0)
+ return;
+
+ dirty_cells.erase(cell);
+
+ HierDirtyFlags *p = this;
+ while (p != nullptr) {
+ p->dirty--;
+ log_assert(p->dirty >= 0);
+ p = p->parent;
+ }
+ }
+};
+
+struct SimplecWorker
+{
+ bool verbose = false;
+ int max_uintsize = 32;
+
+ Design *design;
+ dict<Module*, SigMap> sigmaps;
+ HierDirtyFlags *dirty_flags = nullptr;
+
+ vector<string> signal_declarations;
+ pool<int> generated_sigtypes;
+
+ vector<string> util_declarations;
+ pool<string> generated_utils;
+
+ vector<string> struct_declarations;
+ pool<IdString> generated_structs;
+
+ vector<string> funct_declarations;
+
+ pool<string> reserved_cids;
+ dict<IdString, string> id2cid;
+
+ dict<Module*, dict<SigBit, pool<tuple<Cell*, IdString, int>>>> bit2cell;
+ dict<Module*, dict<SigBit, pool<SigBit>>> bit2output;
+
+ SimplecWorker(Design *design) : design(design)
+ {
+ }
+
+ string sigtype(int n)
+ {
+ string struct_name = stringf("signal%d_t", n);
+
+ if (generated_sigtypes.count(n) == 0)
+ {
+ signal_declarations.push_back("");
+ signal_declarations.push_back(stringf("#ifndef YOSYS_SIMPLEC_SIGNAL%d_T", n));
+ signal_declarations.push_back(stringf("#define YOSYS_SIMPLEC_SIGNAL%d_T", n));
+ signal_declarations.push_back(stringf("typedef struct {"));
+
+ for (int k = 8; k <= max_uintsize; k = 2*k)
+ if (n <= k && k <= max_uintsize) {
+ signal_declarations.push_back(stringf(" uint%d_t value_%d_0 : %d;", k, n-1, n));
+ goto end_struct;
+ }
+
+ for (int k = 0; k < n; k += max_uintsize) {
+ int bits = std::min(max_uintsize, n-k);
+ signal_declarations.push_back(stringf(" uint%d_t value_%d_%d : %d;", max_uintsize, k+bits-1, k, bits));
+ }
+
+ end_struct:
+ signal_declarations.push_back(stringf("} signal%d_t;", n));
+ signal_declarations.push_back(stringf("#endif"));
+ generated_sigtypes.insert(n);
+ }
+
+ return struct_name;
+ }
+
+ void util_ifdef_guard(string s)
+ {
+ for (int i = 0; i < GetSize(s); i++)
+ if ('a' <= s[i] && s[i] <= 'z')
+ s[i] -= 'a' - 'A';
+
+ util_declarations.push_back(stringf("#ifndef %s", s.c_str()));
+ util_declarations.push_back(stringf("#define %s", s.c_str()));
+ }
+
+ string util_get_bit(int n, int idx)
+ {
+ string util_name = stringf("yosys_simplec_get_bit_%d_of_%d", idx, n);
+
+ if (generated_utils.count(util_name) == 0)
+ {
+ util_ifdef_guard(util_name);
+ util_declarations.push_back(stringf("bool %s(const %s *sig)", util_name.c_str(), sigtype(n).c_str()));
+ util_declarations.push_back(stringf("{"));
+
+ int word_idx = idx / max_uintsize, word_offset = idx % max_uintsize;
+ string value_name = stringf("value_%d_%d", std::min(n-1, (word_idx+1)*max_uintsize-1), word_idx*max_uintsize);
+
+ util_declarations.push_back(stringf(" return (sig->%s >> %d) & 1;", value_name.c_str(), word_offset));
+
+ util_declarations.push_back(stringf("}"));
+ util_declarations.push_back(stringf("#endif"));
+ generated_utils.insert(util_name);
+ }
+
+ return util_name;
+ }
+
+ string util_set_bit(int n, int idx)
+ {
+ string util_name = stringf("yosys_simplec_set_bit_%d_of_%d", idx, n);
+
+ if (generated_utils.count(util_name) == 0)
+ {
+ util_ifdef_guard(util_name);
+ util_declarations.push_back(stringf("void %s(%s *sig, bool value)", util_name.c_str(), sigtype(n).c_str()));
+ util_declarations.push_back(stringf("{"));
+
+ int word_idx = idx / max_uintsize, word_offset = idx % max_uintsize;
+ string value_name = stringf("value_%d_%d", std::min(n-1, (word_idx+1)*max_uintsize-1), word_idx*max_uintsize);
+
+ util_declarations.push_back(stringf(" if (value)"));
+ util_declarations.push_back(stringf(" sig->%s |= 1UL << %d;", value_name.c_str(), word_offset));
+ util_declarations.push_back(stringf(" else"));
+ util_declarations.push_back(stringf(" sig->%s &= ~(1UL << %d);", value_name.c_str(), word_offset));
+
+ util_declarations.push_back(stringf("}"));
+ util_declarations.push_back(stringf("#endif"));
+ generated_utils.insert(util_name);
+ }
+
+ return util_name;
+ }
+
+ string cid(IdString id)
+ {
+ if (id2cid.count(id) == 0)
+ {
+ string s = id.str();
+ if (GetSize(s) < 2) log_abort();
+
+ if (s[0] == '\\')
+ s = s.substr(1);
+
+ if ('0' <= s[0] && s[0] <= '9') {
+ s = "_" + s;
+ }
+
+ for (int i = 0; i < GetSize(s); i++) {
+ if ('0' <= s[i] && s[i] <= '9') continue;
+ if ('A' <= s[i] && s[i] <= 'Z') continue;
+ if ('a' <= s[i] && s[i] <= 'z') continue;
+ s[i] = '_';
+ }
+
+ while (reserved_cids.count(s))
+ s += "_";
+
+ reserved_cids.insert(s);
+ id2cid[id] = s;
+ }
+
+ return id2cid.at(id);
+ }
+
+ void create_module_struct(Module *mod)
+ {
+ if (generated_structs.count(mod->name))
+ return;
+
+ generated_structs.insert(mod->name);
+ sigmaps[mod].set(mod);
+
+ for (Wire *w : mod->wires())
+ {
+ if (w->port_output)
+ for (auto bit : SigSpec(w))
+ bit2output[mod][sigmaps.at(mod)(bit)].insert(bit);
+ }
+
+ for (Cell *c : mod->cells())
+ {
+ for (auto &conn : c->connections())
+ {
+ if (!c->input(conn.first))
+ continue;
+
+ int idx = 0;
+ for (auto bit : sigmaps.at(mod)(conn.second))
+ bit2cell[mod][bit].insert(tuple<Cell*, IdString, int>(c, conn.first, idx++));
+ }
+
+ if (design->module(c->type))
+ create_module_struct(design->module(c->type));
+ }
+
+ struct_declarations.push_back("");
+ struct_declarations.push_back(stringf("struct %s_state_t {", cid(mod->name).c_str()));
+
+ for (Wire *w : mod->wires())
+ struct_declarations.push_back(stringf(" %s %s; // %s", sigtype(w->width).c_str(), cid(w->name).c_str(), log_id(w)));
+
+ for (Cell *c : mod->cells())
+ if (design->module(c->type))
+ struct_declarations.push_back(stringf(" struct %s_state_t %s; // %s", cid(c->type).c_str(), cid(c->name).c_str(), log_id(c)));
+
+ struct_declarations.push_back(stringf("};"));
+ }
+
+ void eval_cell(HierDirtyFlags *work, string &prefix, string &/* log_prefix */, Cell *cell)
+ {
+ if (cell->type.in("$_AND_", "$_NAND_", "$_OR_", "$_NOR_", "$_XOR_", "$_XNOR"))
+ {
+ SigBit a = sigmaps.at(work->module)(cell->getPort("\\A"));
+ SigBit b = sigmaps.at(work->module)(cell->getPort("\\B"));
+ SigBit y = sigmaps.at(work->module)(cell->getPort("\\Y"));
+
+ string a_expr = a.wire ? stringf("%s(&%s)", util_get_bit(a.wire->width, a.offset).c_str(), (prefix + cid(a.wire->name)).c_str()) : a.data ? "1" : "0";
+ string b_expr = b.wire ? stringf("%s(&%s)", util_get_bit(b.wire->width, b.offset).c_str(), (prefix + cid(b.wire->name)).c_str()) : b.data ? "1" : "0";
+ string expr;
+
+ if (cell->type == "$_AND_") expr = stringf("%s & %s", a_expr.c_str(), b_expr.c_str());
+ if (cell->type == "$_NAND_") expr = stringf("!(%s & %s)", a_expr.c_str(), b_expr.c_str());
+ if (cell->type == "$_OR_") expr = stringf("%s | %s", a_expr.c_str(), b_expr.c_str());
+ if (cell->type == "$_NOR_") expr = stringf("!(%s | %s)", a_expr.c_str(), b_expr.c_str());
+ if (cell->type == "$_XOR_") expr = stringf("%s ^ %s", a_expr.c_str(), b_expr.c_str());
+ if (cell->type == "$_XNOR_") expr = stringf("!(%s ^ %s)", a_expr.c_str(), b_expr.c_str());
+
+ log_assert(y.wire);
+ funct_declarations.push_back(stringf(" %s(&%s, %s); // %s (%s)", util_set_bit(y.wire->width, y.offset).c_str(),
+ (prefix + cid(y.wire->name)).c_str(), expr.c_str(), log_id(cell), log_id(cell->type)));
+
+ work->set_dirty(y);
+ return;
+ }
+
+ log_error("No C model for %s available at the moment (FIXME).\n", log_id(cell->type));
+ }
+
+ void eval_dirty(HierDirtyFlags *work, string prefix, string log_prefix, string parent_prefix)
+ {
+ while (work->dirty)
+ {
+ while (!work->dirty_bits.empty() || !work->dirty_cells.empty())
+ {
+ if (!work->dirty_bits.empty())
+ {
+ SigSpec dirtysig(work->dirty_bits);
+ dirtysig.sort_and_unify();
+
+ for (SigChunk chunk : dirtysig.chunks())
+ funct_declarations.push_back(stringf(" // New dirty bits in %s: %s", log_prefix.c_str(), log_signal(chunk)));
+
+ for (SigBit bit : dirtysig)
+ {
+ if (bit2output[work->module].count(bit) && work->parent)
+ for (auto outbit : bit2output[work->module][bit])
+ {
+ Module *parent_mod = work->parent->module;
+ Cell *parent_cell = parent_mod->cell(work->hiername);
+
+ IdString port_name = outbit.wire->name;
+ int port_offset = outbit.offset;
+ SigBit parent_bit = sigmaps.at(parent_mod)(parent_cell->getPort(port_name)[port_offset]);
+
+ log_assert(bit.wire && parent_bit.wire);
+ funct_declarations.push_back(stringf(" %s(&%s, %s(&%s));",
+ util_set_bit(parent_bit.wire->width, parent_bit.offset).c_str(),
+ (parent_prefix + cid(parent_bit.wire->name)).c_str(),
+ util_get_bit(bit.wire->width, bit.offset).c_str(),
+ (prefix + cid(bit.wire->name)).c_str()));
+ work->parent->set_dirty(parent_bit);
+ }
+
+ for (auto &port : bit2cell[work->module][bit])
+ {
+ if (work->children.count(std::get<0>(port)->name)) {
+ HierDirtyFlags *child = work->children.at(std::get<0>(port)->name);
+ SigBit child_bit = sigmaps.at(child->module)(SigBit(child->module->wire(std::get<1>(port)), std::get<2>(port)));
+ log_assert(bit.wire && child_bit.wire);
+ funct_declarations.push_back(stringf(" %s(&%s, %s(&%s));",
+ util_set_bit(child_bit.wire->width, child_bit.offset).c_str(),
+ (prefix + cid(child->hiername) + "." + cid(child_bit.wire->name)).c_str(),
+ util_get_bit(bit.wire->width, bit.offset).c_str(),
+ (prefix + cid(bit.wire->name)).c_str()));
+ child->set_dirty(child_bit);
+ } else {
+ work->set_dirty(std::get<0>(port));
+ }
+ }
+ work->unset_dirty(bit);
+ }
+ }
+
+ if (!work->dirty_cells.empty())
+ {
+ Cell *cell = *work->dirty_cells.begin();
+ eval_cell(work, prefix, log_prefix, cell);
+ work->unset_dirty(cell);
+ }
+ }
+
+ for (auto &child : work->children)
+ eval_dirty(child.second, prefix + cid(child.first) + ".", log_prefix + "." + cid(child.first), prefix);
+ }
+ }
+
+ void run(Module *mod)
+ {
+ create_module_struct(mod);
+
+ dirty_flags = new HierDirtyFlags(mod, IdString(), nullptr);
+
+ funct_declarations.push_back("");
+ funct_declarations.push_back(stringf("void %s_init(struct %s_state_t *state)", cid(mod->name).c_str(), cid(mod->name).c_str()));
+ funct_declarations.push_back("{");
+ funct_declarations.push_back("}");
+
+ funct_declarations.push_back("");
+ funct_declarations.push_back(stringf("void %s_eval(struct %s_state_t *state)", cid(mod->name).c_str(), cid(mod->name).c_str()));
+ funct_declarations.push_back("{");
+
+ for (Wire *w : mod->wires()) {
+ if (w->port_input)
+ for (SigBit bit : sigmaps.at(mod)(w))
+ dirty_flags->set_dirty(bit);
+ }
+
+ eval_dirty(dirty_flags, "state->", log_id(mod), "");
+
+ funct_declarations.push_back("}");
+
+ funct_declarations.push_back("");
+ funct_declarations.push_back(stringf("void %s_tick(struct %s_state_t *state)", cid(mod->name).c_str(), cid(mod->name).c_str()));
+ funct_declarations.push_back("{");
+ funct_declarations.push_back("}");
+
+ delete dirty_flags;
+ dirty_flags = nullptr;
+ }
+
+ void write(std::ostream &f)
+ {
+ f << "#include <stdint.h>" << std::endl;
+ f << "#include <stdbool.h>" << std::endl;
+
+ for (auto &line : signal_declarations)
+ f << line << std::endl;
+
+ for (auto &line : util_declarations)
+ f << line << std::endl;
+
+ for (auto &line : struct_declarations)
+ f << line << std::endl;
+
+ for (auto &line : funct_declarations)
+ f << line << std::endl;
+ }
+};
+
+struct SimplecBackend : public Backend {
+ SimplecBackend() : Backend("simplec", "convert design to simple C code") { }
+ virtual void help()
+ {
+ // |---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|
+ log("\n");
+ log(" write_simplec [options] [filename]\n");
+ log("\n");
+ log("Write simple C code for simulating the design. The C code writen can be used to\n");
+ log("simulate the design in a C environment, but the purpose of this command is to\n");
+ log("generate code that works well with C-based formal verification.\n");
+ log("\n");
+ log(" -verbose\n");
+ log(" this will print the recursive walk used to export the modules.\n");
+ log("\n");
+ log(" -i8, -i16, -i32, -i64\n");
+ log(" set the maximum integer bit width to use in the generated code.\n");
+ log("\n");
+ log("THIS COMMAND IS UNDER CONSTRUCTION\n");
+ log("\n");
+ }
+ virtual void execute(std::ostream *&f, std::string filename, std::vector<std::string> args, RTLIL::Design *design)
+ {
+ SimplecWorker worker(design);
+
+ log_header(design, "Executing SIMPLEC backend.\n");
+
+ size_t argidx;
+ for (argidx = 1; argidx < args.size(); argidx++)
+ {
+ if (args[argidx] == "-verbose") {
+ worker.verbose = true;
+ continue;
+ }
+ if (args[argidx] == "-i8") {
+ worker.max_uintsize = 8;
+ continue;
+ }
+ if (args[argidx] == "-i16") {
+ worker.max_uintsize = 16;
+ continue;
+ }
+ if (args[argidx] == "-i32") {
+ worker.max_uintsize = 32;
+ continue;
+ }
+ if (args[argidx] == "-i64") {
+ worker.max_uintsize = 64;
+ continue;
+ }
+ break;
+ }
+ extra_args(f, filename, args, argidx);
+
+ Module *topmod = design->top_module();
+
+ if (topmod == nullptr)
+ log_error("Current design has no top module.\n");
+
+ worker.run(topmod);
+ worker.write(*f);
+ }
+} SimplecBackend;
+
+PRIVATE_NAMESPACE_END
diff --git a/backends/simplec/test00.sh b/backends/simplec/test00.sh
new file mode 100644
index 000000000..6a7560da0
--- /dev/null
+++ b/backends/simplec/test00.sh
@@ -0,0 +1,5 @@
+#!/bin/bash
+set -ex
+../../yosys -p 'synth -top test; write_simplec -i8 test00_uut.c' test00_uut.v
+clang -o test00_tb test00_tb.c
+./test00_tb
diff --git a/backends/simplec/test00_tb.c b/backends/simplec/test00_tb.c
new file mode 100644
index 000000000..650f121ca
--- /dev/null
+++ b/backends/simplec/test00_tb.c
@@ -0,0 +1,78 @@
+#include <stdio.h>
+#include <assert.h>
+#include "test00_uut.c"
+
+uint32_t xorshift32()
+{
+ static uint32_t x32 = 314159265;
+ x32 ^= x32 << 13;
+ x32 ^= x32 >> 17;
+ x32 ^= x32 << 5;
+ return x32;
+}
+
+int main()
+{
+ struct test_state_t state;
+ uint32_t a, b, c, x, y, z;
+
+ for (int i = 0; i < 100; i++)
+ {
+ a = xorshift32();
+ b = xorshift32();
+ c = xorshift32();
+
+ x = (a & b) | c;
+ y = a & (b | c);
+ z = a ^ b ^ c;
+
+ state.a.value_7_0 = a;
+ state.a.value_15_8 = a >> 8;
+ state.a.value_23_16 = a >> 16;
+ state.a.value_31_24 = a >> 24;
+
+ state.b.value_7_0 = b;
+ state.b.value_15_8 = b >> 8;
+ state.b.value_23_16 = b >> 16;
+ state.b.value_31_24 = b >> 24;
+
+ state.c.value_7_0 = c;
+ state.c.value_15_8 = c >> 8;
+ state.c.value_23_16 = c >> 16;
+ state.c.value_31_24 = c >> 24;
+
+ test_eval(&state);
+
+ uint32_t uut_x = 0;
+ uut_x |= (uint32_t)state.x.value_7_0;
+ uut_x |= (uint32_t)state.x.value_15_8 << 8;
+ uut_x |= (uint32_t)state.x.value_23_16 << 16;
+ uut_x |= (uint32_t)state.x.value_31_24 << 24;
+
+ uint32_t uut_y = 0;
+ uut_y |= (uint32_t)state.y.value_7_0;
+ uut_y |= (uint32_t)state.y.value_15_8 << 8;
+ uut_y |= (uint32_t)state.y.value_23_16 << 16;
+ uut_y |= (uint32_t)state.y.value_31_24 << 24;
+
+ uint32_t uut_z = 0;
+ uut_z |= (uint32_t)state.z.value_7_0;
+ uut_z |= (uint32_t)state.z.value_15_8 << 8;
+ uut_z |= (uint32_t)state.z.value_23_16 << 16;
+ uut_z |= (uint32_t)state.z.value_31_24 << 24;
+
+ printf("---\n");
+ printf("A: 0x%08x\n", a);
+ printf("B: 0x%08x\n", b);
+ printf("C: 0x%08x\n", c);
+ printf("X: 0x%08x 0x%08x\n", x, uut_x);
+ printf("Y: 0x%08x 0x%08x\n", y, uut_y);
+ printf("Z: 0x%08x 0x%08x\n", z, uut_z);
+
+ assert(x == uut_x);
+ assert(y == uut_y);
+ assert(z == uut_z);
+ }
+
+ return 0;
+}
diff --git a/backends/simplec/test00_uut.v b/backends/simplec/test00_uut.v
new file mode 100644
index 000000000..fd634cf82
--- /dev/null
+++ b/backends/simplec/test00_uut.v
@@ -0,0 +1,14 @@
+module test(input [31:0] a, b, c, output [31:0] x, y, z);
+ unit_x unit_x_inst (.a(a), .b(b), .c(c), .x(x));
+ unit_y unit_y_inst (.a(a), .b(b), .c(c), .y(y));
+ assign z = a ^ b ^ c;
+endmodule
+
+module unit_x(input [31:0] a, b, c, output [31:0] x);
+ assign x = (a & b) | c;
+endmodule
+
+module unit_y(input [31:0] a, b, c, output [31:0] y);
+ assign y = a & (b | c);
+endmodule
+
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