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[Qemu-devel] [PATCH] x86_64: optimise muldiv64 for x86_64 architecture


From: Frediano Ziglio
Subject: [Qemu-devel] [PATCH] x86_64: optimise muldiv64 for x86_64 architecture
Date: Fri, 9 Jan 2015 09:53:08 +0000

As this platform can do multiply/divide using 128 bit precision use
these instruction to implement it.

Signed-off-by: Frediano Ziglio <address@hidden>
---
 include/qemu-common.h | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/include/qemu-common.h b/include/qemu-common.h
index f862214..5366220 100644
--- a/include/qemu-common.h
+++ b/include/qemu-common.h
@@ -370,6 +370,7 @@ static inline uint8_t from_bcd(uint8_t val)
 }
 
 /* compute with 96 bit intermediate result: (a*b)/c */
+#ifndef __x86_64__
 static inline uint64_t muldiv64(uint64_t a, uint32_t b, uint32_t c)
 {
     union {
@@ -392,6 +393,18 @@ static inline uint64_t muldiv64(uint64_t a, uint32_t b, 
uint32_t c)
     res.l.low = (((rh % c) << 32) + (rl & 0xffffffff)) / c;
     return res.ll;
 }
+#else
+static inline uint64_t muldiv64(uint64_t a, uint32_t b, uint32_t c)
+{
+    uint64_t res;
+
+    asm ("mulq %2\n\tdivq %3"
+         : "=a"(res)
+         : "a"(a), "qm"((uint64_t) b), "qm"((uint64_t)c)
+         : "rdx", "cc");
+    return res;
+}
+#endif
 
 /* Round number down to multiple */
 #define QEMU_ALIGN_DOWN(n, m) ((n) / (m) * (m))
-- 
1.9.1





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