media/base/djb2.h

   1 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef MEDIA_BASE_DJB2_H_
   6 #define MEDIA_BASE_DJB2_H_
   7
   8 #include "base/basictypes.h"
   9 #include "media/base/media_export.h"
  10
  11 // DJB2 is a hash algorithm with excellent distribution and speed
  12 // on many different sets.
  13 // It has marginally more collisions than FNV1, but makes up for it in
  14 // performance.
  15 // The return value is suitable for table lookups.
  16 // For small fixed sizes (ie a pixel), it has low overhead and inlines well.
  17 // For large data sets, it optimizes into assembly/simd and is appropriate
  18 // for realtime applications.
  19 // See Also:
  20 //   http://www.cse.yorku.ca/~oz/hash.html
  21
  22 static const uint32 kDJB2HashSeed = 5381u;
  23
  24 // These functions perform DJB2 hash. The simplest call is DJB2Hash() to
  25 // generate the DJB2 hash of the given data:
  26 //   uint32 hash = DJB2Hash(data1, length1, kDJB2HashSeed);
  27 //
  28 // You can also compute the DJB2 hash of data incrementally by making multiple
  29 // calls to DJB2Hash():
  30 //   uint32 hash_value = kDJB2HashSeed;  // Initial seed for DJB2.
  31 //   for (size_t i = 0; i < copy_lines; ++i) {
  32 //     hash_value = DJB2Hash(source, bytes_per_line, hash_value);
  33 //     source += source_stride;
  34 //   }
  35
  36 // For the given buffer of data, compute the DJB2 hash of
  37 // the data. You can call this any number of times during the computation.
  38 MEDIA_EXPORT uint32 DJB2Hash(const void* buf, size_t len, uint32 seed);
  39
  40 #endif  // MEDIA_BASE_DJB2_H_
  41