Moved SuperFastHash function from base/hash.cc to base/third_party.

base/hash.cc

-// From http://www.azillionmonkeys.com/qed/hash.html
+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
 
 #include "base/hash.h"
 
-typedef uint32 uint32_t;
-typedef uint16 uint16_t;
-
 namespace base {
 
-#undef get16bits
-#if (defined(__GNUC__) && defined(__i386__)) || defined(__WATCOMC__) \
-  || defined(_MSC_VER) || defined (__BORLANDC__) || defined (__TURBOC__)
-#define get16bits(d) (*((const uint16_t *) (d)))
-#endif
-
-#if !defined (get16bits)
-#define get16bits(d) ((((uint32_t)(((const uint8_t *)(d))[1])) << 8)\
-                       +(uint32_t)(((const uint8_t *)(d))[0]) )
-#endif
-
-uint32 SuperFastHash(const char * data, int len) {
-  uint32_t hash = len, tmp;
-  int rem;
-
-  if (len <= 0 || data == NULL)
-    return 0;
-
-  rem = len & 3;
-  len >>= 2;
-
-  /* Main loop */
-  for (; len > 0; len--) {
-    hash  += get16bits(data);
-    tmp    = (get16bits(data + 2) << 11) ^ hash;
-    hash   = (hash << 16) ^ tmp;
-    data  += 2 * sizeof(uint16_t);
-    hash  += hash >> 11;
-  }
-
-  /* Handle end cases */
-  switch (rem) {
-    case 3:
-      hash += get16bits(data);
-      hash ^= hash << 16;
-
-      // Treat the final character as signed. This ensures all platforms behave
-      // consistently with the original x86 code.
-      hash ^= static_cast<signed char>(data[sizeof(uint16_t)]) << 18;
-      hash += hash >> 11;
-      break;
-    case 2:
-      hash += get16bits(data);
-      hash ^= hash << 11;
-      hash += hash >> 17;
-      break;
-    case 1:
-      hash += static_cast<signed char>(*data);
-      hash ^= hash << 10;
-      hash += hash >> 1;
-  }
-
-  /* Force "avalanching" of final 127 bits */
-  hash ^= hash << 3;
-  hash += hash >> 5;
-  hash ^= hash << 4;
-  hash += hash >> 17;
-  hash ^= hash << 25;
-  hash += hash >> 6;
-
-  return hash;
+uint32 SuperFastHash(const char* data, int len) {
+  return ::SuperFastHash(data, len);

[Matt Giuca, 2014/02/27 03:14:09]

Note: This added indirection may introduce a slight performance regression,
since we now need to call across to another function in a different module (I
looked at the assembly code on Linux; it compiles to an extra jump).

This is probably nothing to worry about, but if we are extremely worried about
performance here, we could directly export the SuperFastHash function from
superfasthash.c (which would require modifying the third_party code to import
base/base_export.h -- it's messier so I'm not in favour of it unless absolutely
necessary).

 }
 
 }  // namespace base