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Change hash computation for transcendental cache to use arithmetic

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shifts. Leads to fewer collisions.

Review URL: http://codereview.chromium.org/2809012

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@4872 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
This commit is contained in:
ager@chromium.org 2010-06-16 08:29:25 +00:00
parent 52975ae407
commit ed0fc41723
4 changed files with 12 additions and 12 deletions
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6
src/arm/codegen-arm.cc
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@ -8304,11 +8304,11 @@ void TranscendentalCacheStub::Generate(MacroAssembler* masm) {
__ 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));

4
src/heap.h
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@ -1882,8 +1882,8 @@ class TranscendentalCache {
};
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));
}

6
src/ia32/codegen-ia32.cc
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@ -10293,15 +10293,15 @@ void TranscendentalCacheStub::Generate(MacroAssembler* masm) {
// 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));

8
src/x64/codegen-x64.cc
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@ -8177,7 +8177,7 @@ void TranscendentalCacheStub::Generate(MacroAssembler* masm) {
// 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 @@ void TranscendentalCacheStub::Generate(MacroAssembler* masm) {
__ 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);