From 4f2c734821acfa5cbba93d2bf9fa204f4767ce61 Mon Sep 17 00:00:00 2001
From: Evan Martin <martine@danga.com>
Date: Thu, 12 Jan 2012 11:16:51 -0800
Subject: decide on murmur hash, delete stl hash

A nice thing about working on Google: a C++ expert who happened
to be writing a proposal on hashing for the next C++ version
wandered into my office.  He seemed to think using Murmur here
is fine.
---
 src/hash_map.h | 22 ++++------------------
 1 file changed, 4 insertions(+), 18 deletions(-)

diff --git a/src/hash_map.h b/src/hash_map.h
index d3e9c51..88c2681 100644
--- a/src/hash_map.h
+++ b/src/hash_map.h
@@ -17,24 +17,21 @@
 
 #include "string_piece.h"
 
-static const unsigned int kSeed = 0xDECAFBAD;
 // MurmurHash2, by Austin Appleby
 static inline
-unsigned int MurmurHash2(const void* key, int len, unsigned int seed) {
+unsigned int MurmurHash2(const void* key, int len) {
+  static const unsigned int seed = 0xDECAFBAD;
   const unsigned int m = 0x5bd1e995;
   const int r = 24;
   unsigned int h = seed ^ len;
   const unsigned char * data = (const unsigned char *)key;
   while(len >= 4) {
     unsigned int k = *(unsigned int *)data;
-
     k *= m;
     k ^= k >> r;
     k *= m;
-
     h *= m;
     h ^= k;
-
     data += 4;
     len -= 4;
   }
@@ -44,23 +41,12 @@ unsigned int MurmurHash2(const void* key, int len, unsigned int seed) {
   case 1: h ^= data[0];
     h *= m;
   };
-
   h ^= h >> 13;
   h *= m;
   h ^= h >> 15;
-
   return h;
 }
 
-static inline size_t StlHash(StringPiece str) {
-  const char* p = str.str_;
-  int len = str.len_;
-  size_t hash = 0;
-  while (len--)
-    hash = 5 * hash + *p++;
-  return hash;
-}
-
 #ifdef _MSC_VER
 #include <hash_map>
 
@@ -69,7 +55,7 @@ using stdext::hash_compare;
 
 struct StringPieceCmp : public hash_compare<StringPiece> {
   size_t operator()(const StringPiece& key) const {
-    return MurmurHash2(key.str_, key.len_, kSeed);
+    return MurmurHash2(key.str_, key.len_);
   }
   bool operator()(const StringPiece& a, const StringPiece& b) const {
     int cmp = strncmp(a.str_, b.str_, min(a.len_, b.len_));
@@ -100,7 +86,7 @@ struct hash<std::string> {
 template<>
 struct hash<StringPiece> {
   size_t operator()(StringPiece key) const {
-    return MurmurHash2(key.str_, key.len_, kSeed);
+    return MurmurHash2(key.str_, key.len_);
   }
 };
 
-- 
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