Move muldiv64 out and make it as a public function.

muldiv64 is used to caculate u64*u32/u32, and we
will use it for TSC scaling.

Signed-off-by: Xiantao Zhang <xiantao.zhang@intel.com>
Signed-off-by: Keir Fraser <keir.fraser@citrix.com>

1 files changed, 29 insertions, 0 deletions

diff --git a/xen/common/lib.c b/xen/common/lib.c
index 2f1a005ca4..579512a4c5 100644
--- a/xen/common/lib.c
+++ b/xen/common/lib.c
@@ -401,6 +401,35 @@ s64 __moddi3(s64 a, s64 b)
 
 #endif /* BITS_PER_LONG == 32 */
 
+/* Compute with 96 bit intermediate result: (a*b)/c */
+uint64_t muldiv64(uint64_t a, uint32_t b, uint32_t c)
+{
+#ifdef __x86_64__
+    asm ( "mul %%rdx; div %%rcx" : "=a" (a) : "0" (a), "d" (b), "c" (c) );
+    return a;
+#else
+    union {
+        uint64_t ll;
+        struct {
+#ifdef WORDS_BIGENDIAN
+            uint32_t high, low;
+#else
+            uint32_t low, high;
+#endif            
+        } l;
+    } u, res;
+    uint64_t rl, rh;
+
+    u.ll = a;
+    rl = (uint64_t)u.l.low * (uint64_t)b;
+    rh = (uint64_t)u.l.high * (uint64_t)b;
+    rh += (rl >> 32);
+    res.l.high = rh / c;
+    res.l.low = (((rh % c) << 32) + (rl & 0xffffffff)) / c;
+    return res.ll;
+#endif
+}
+
 unsigned long long parse_size_and_unit(const char *s, const char **ps)
 {
     unsigned long long ret;