Cast: Logging estimates clock difference based on packets

media/cast/common/mod_util.h

+// 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.
+
+#ifndef MEDIA_CAST_COMMON_MOD_UTIL_H_
+#define MEDIA_CAST_COMMON_MOD_UTIL_H_
+
+#include <map>
+#include "base/logging.h"
+
+namespace media {
+namespace cast {
+
+// MAP is a map<uint??, ...> where the unsigned integer is
+// assumed to wrap around, but only a small range is used at a time.
+// Return the oldest entry in the map.
+template<class MAP>
+typename MAP::iterator ModMapOldest(MAP* map) {
+  typename MAP::iterator ret = map->begin();
+  if (ret != map->end()) {
+    typename MAP::key_type lower_quarter = 0;
+    lower_quarter--;
+    lower_quarter >>= 1;
+    if (ret->first < lower_quarter) {
+      typename MAP::iterator tmp = map->upper_bound(lower_quarter * 3);
+      if (tmp != map->end())
+        ret = tmp;
+    }
+  }
+  return ret;
+}
+
+// MAP is a map<uint??, ...> where the unsigned integer is
+// assumed to wrap around, but only a small range is used at a time.
+// Returns the previous entry in the map.
+template<class MAP>
+typename MAP::iterator ModMapPrevious(MAP* map, typename MAP::iterator i) {
+  DCHECK(!map->empty());
+  typename MAP::iterator ret = i;
+  if (i == map->begin()) {
+    ret = map->end();
+  }
+  ret--;
+  if (i == ret)
+    return map->end();
+  if ((i->first - ret->first) > ((typename MAP::key_type(0) - 1)) >> 1)
+    return map->end();
+  return ret;
+}
+
+}  // namespace cast
+}  // namespace media
+
+#endif