From ed0fc417235b909ee3f67d696614c2239d95b844 Mon Sep 17 00:00:00 2001
From: "ager@chromium.org"
 <ager@chromium.org@ce2b1a6d-e550-0410-aec6-3dcde31c8c00>
Date: Wed, 16 Jun 2010 08:29:25 +0000
Subject: [PATCH] Change hash computation for transcendental cache to use
 arithmetic 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
---
 src/arm/codegen-arm.cc   | 6 +++---
 src/heap.h               | 4 ++--
 src/ia32/codegen-ia32.cc | 6 +++---
 src/x64/codegen-x64.cc   | 8 ++++----
 4 files changed, 12 insertions(+), 12 deletions(-)

diff --git a/src/arm/codegen-arm.cc b/src/arm/codegen-arm.cc
index 325e67a..a2eb717 100644
--- a/src/arm/codegen-arm.cc
+++ b/src/arm/codegen-arm.cc
@@ -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));
 
diff --git a/src/heap.h b/src/heap.h
index 0db4008..8386e73 100644
--- a/src/heap.h
+++ b/src/heap.h
@@ -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));
   }
 
diff --git a/src/ia32/codegen-ia32.cc b/src/ia32/codegen-ia32.cc
index 521e4fe..4471d8c 100644
--- a/src/ia32/codegen-ia32.cc
+++ b/src/ia32/codegen-ia32.cc
@@ -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));
diff --git a/src/x64/codegen-x64.cc b/src/x64/codegen-x64.cc
index 1201ace..d5be787 100644
--- a/src/x64/codegen-x64.cc
+++ b/src/x64/codegen-x64.cc
@@ -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);
-- 
2.7.4