Reviewers: Erik Corry,
Description:
Change hash computation for transcendental cache to use arithmetic
shifts. Leads to fewer collisions.
Please review this at http://codereview.chromium.org/2809012/show
SVN Base: http://v8.googlecode.com/svn/branches/bleeding_edge/
Affected files:
M src/arm/codegen-arm.cc
M src/heap.h
M src/ia32/codegen-ia32.cc
M src/x64/codegen-x64.cc
Index: src/arm/codegen-arm.cc
===================================================================
--- src/arm/codegen-arm.cc (revision 4871)
+++ src/arm/codegen-arm.cc (working copy)
@@ -8304,11 +8304,11 @@
__ bind(&loaded);
// r2 = low 32 bits of double value
// r3 = high 32 bits of double value
- // Compute hash:
+ // Compute hash (the shifts are arithmetic):
// h = (low ^ high); h ^= h >> 16; h ^= h >> 8; h = h & (cacheSize -
1);
__ eor(r1, r2, Operand(r3));
- __ eor(r1, r1, Operand(r1, LSR, 16));
- __ eor(r1, r1, Operand(r1, LSR, 8));
+ __ eor(r1, r1, Operand(r1, ASR, 16));
+ __ eor(r1, r1, Operand(r1, ASR, 8));
ASSERT(IsPowerOf2(TranscendentalCache::kCacheSize));
__ And(r1, r1, Operand(TranscendentalCache::kCacheSize - 1));
Index: src/heap.h
===================================================================
--- src/heap.h (revision 4871)
+++ src/heap.h (working copy)
@@ -1882,8 +1882,8 @@
};
inline static int Hash(const Converter& c) {
uint32_t hash = (c.integers[0] ^ c.integers[1]);
- hash ^= hash >> 16;
- hash ^= hash >> 8;
+ hash ^= static_cast<int32_t>(hash) >> 16;
+ hash ^= static_cast<int32_t>(hash) >> 8;
return (hash & (kCacheSize - 1));
}
Index: src/ia32/codegen-ia32.cc
===================================================================
--- src/ia32/codegen-ia32.cc (revision 4871)
+++ src/ia32/codegen-ia32.cc (working copy)
@@ -10293,15 +10293,15 @@
// ST[0] == double value
// ebx = low 32 bits of double value
// edx = high 32 bits of double value
- // Compute hash:
+ // Compute hash (the shifts are arithmetic):
// h = (low ^ high); h ^= h >> 16; h ^= h >> 8; h = h & (cacheSize -
1);
__ mov(ecx, ebx);
__ xor_(ecx, Operand(edx));
__ mov(eax, ecx);
- __ shr(eax, 16);
+ __ sar(eax, 16);
__ xor_(ecx, Operand(eax));
__ mov(eax, ecx);
- __ shr(eax, 8);
+ __ sar(eax, 8);
__ xor_(ecx, Operand(eax));
ASSERT(IsPowerOf2(TranscendentalCache::kCacheSize));
__ and_(Operand(ecx), Immediate(TranscendentalCache::kCacheSize - 1));
Index: src/x64/codegen-x64.cc
===================================================================
--- src/x64/codegen-x64.cc (revision 4871)
+++ src/x64/codegen-x64.cc (working copy)
@@ -8177,7 +8177,7 @@
// ST[0] == double value
// rbx = bits of double value.
// rdx = also bits of double value.
- // Compute hash (h is 32 bits, bits are 64):
+ // Compute hash (h is 32 bits, bits are 64 and the shifts are
arithmetic):
// h = h0 = bits ^ (bits >> 32);
// h ^= h >> 16;
// h ^= h >> 8;
@@ -8188,9 +8188,9 @@
__ movl(rcx, rdx);
__ movl(rax, rdx);
__ movl(rdi, rdx);
- __ shrl(rdx, Immediate(8));
- __ shrl(rcx, Immediate(16));
- __ shrl(rax, Immediate(24));
+ __ sarl(rdx, Immediate(8));
+ __ sarl(rcx, Immediate(16));
+ __ sarl(rax, Immediate(24));
__ xorl(rcx, rdx);
__ xorl(rax, rdi);
__ xorl(rcx, rax);
--
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