media/cast/common/mod_util.h

   1 // Copyright 2014 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_CAST_COMMON_MOD_UTIL_H_
   6 #define MEDIA_CAST_COMMON_MOD_UTIL_H_
   7
   8 #include <map>
   9 #include "base/logging.h"
  10
  11 namespace media {
  12 namespace cast {
  13
  14 // MAP is a map<uint??, ...> where the unsigned integer is
  15 // assumed to wrap around, but only a small range is used at a time.
  16 // Return the oldest entry in the map.
  17 template<class MAP>
  18 typename MAP::iterator ModMapOldest(MAP* map) {
  19   typename MAP::iterator ret = map->begin();
  20   if (ret != map->end()) {
  21     typename MAP::key_type lower_quarter = 0;
  22     lower_quarter--;
  23     lower_quarter >>= 1;
  24     if (ret->first < lower_quarter) {
  25       typename MAP::iterator tmp = map->upper_bound(lower_quarter * 3);
  26       if (tmp != map->end())
  27         ret = tmp;
  28     }
  29   }
  30   return ret;
  31 }
  32
  33 // MAP is a map<uint??, ...> where the unsigned integer is
  34 // assumed to wrap around, but only a small range is used at a time.
  35 // Returns the previous entry in the map.
  36 template<class MAP>
  37 typename MAP::iterator ModMapPrevious(MAP* map, typename MAP::iterator i) {
  38   DCHECK(!map->empty());
  39   typename MAP::iterator ret = i;
  40   if (i == map->begin()) {
  41     ret = map->end();
  42   }
  43   ret--;
  44   if (i == ret)
  45     return map->end();
  46   if ((i->first - ret->first) > ((typename MAP::key_type(0) - 1)) >> 1)
  47     return map->end();
  48   return ret;
  49 }
  50
  51 }  // namespace cast
  52 }  // namespace media
  53
  54 #endif