Moved sequence number specific operations from mod_ops.h
to sequence_number_util.h
Also in this CL:
- Implemented a MinDiff function which finds the smallest diff of two
wrapping numbers.
- Implemented comparators for sequence numbers.
BUG=
R=mflodman@webrtc.org, tommi@webrtc.org, torbjorng@webrtc.org
Review URL: https://codereview.webrtc.org/1814753002 .
Cr-Commit-Position: refs/heads/master@{#12083}
diff --git a/webrtc/modules/video_coding/sequence_number_util.h b/webrtc/modules/video_coding/sequence_number_util.h
new file mode 100644
index 0000000..828e68a
--- /dev/null
+++ b/webrtc/modules/video_coding/sequence_number_util.h
@@ -0,0 +1,110 @@
+/*
+ * Copyright (c) 2016 The WebRTC project authors. All Rights Reserved.
+ *
+ * Use of this source code is governed by a BSD-style license
+ * that can be found in the LICENSE file in the root of the source
+ * tree. An additional intellectual property rights grant can be found
+ * in the file PATENTS. All contributing project authors may
+ * be found in the AUTHORS file in the root of the source tree.
+ */
+
+#ifndef WEBRTC_MODULES_VIDEO_CODING_SEQUENCE_NUMBER_UTIL_H_
+#define WEBRTC_MODULES_VIDEO_CODING_SEQUENCE_NUMBER_UTIL_H_
+
+#include <limits>
+#include <type_traits>
+
+#include "webrtc/base/mod_ops.h"
+
+namespace webrtc {
+
+// Test if the sequence number |a| is ahead or at sequence number |b|.
+//
+// If |M| is an even number and the two sequence numbers are at max distance
+// from each other, then the sequence number with the highest value is
+// considered to be ahead.
+template <typename T, T M>
+inline bool AheadOrAt(T a, T b) {
+ static_assert(std::is_unsigned<T>::value,
+ "Type must be an unsigned integer.");
+ const T maxDist = M / 2;
+ if (!(M & 1) && MinDiff<T, M>(a, b) == maxDist)
+ return b < a;
+ return ForwardDiff<T, M>(b, a) <= maxDist;
+}
+
+template <typename T>
+inline bool AheadOrAt(T a, T b) {
+ static_assert(std::is_unsigned<T>::value,
+ "Type must be an unsigned integer.");
+ const T maxDist = std::numeric_limits<T>::max() / 2 + T(1);
+ if (a - b == maxDist)
+ return b < a;
+ return ForwardDiff(b, a) < maxDist;
+}
+
+// Test if the sequence number |a| is ahead of sequence number |b|.
+//
+// If |M| is an even number and the two sequence numbers are at max distance
+// from each other, then the sequence number with the highest value is
+// considered to be ahead.
+template <typename T, T M>
+inline bool AheadOf(T a, T b) {
+ static_assert(std::is_unsigned<T>::value,
+ "Type must be an unsigned integer.");
+ return a != b && AheadOrAt<T, M>(a, b);
+}
+
+template <typename T>
+inline bool AheadOf(T a, T b) {
+ static_assert(std::is_unsigned<T>::value,
+ "Type must be an unsigned integer.");
+ return a != b && AheadOrAt(a, b);
+}
+
+namespace internal {
+
+template <typename T, typename M>
+struct SeqNumComp;
+
+template <typename T, T M>
+struct SeqNumComp<T, std::integral_constant<T, M>> {
+ bool operator()(T a, T b) const { return AheadOf<T, M>(a, b); }
+};
+
+template <typename T>
+struct SeqNumComp<T, std::integral_constant<T, T(0)>> {
+ bool operator()(T a, T b) const { return AheadOf<T>(a, b); }
+};
+
+} // namespace internal
+
+// Comparator used to compare sequence numbers in a continuous fashion.
+//
+// WARNING! If used to sort sequence numbers of length M then the interval
+// covered by the sequence numbers may not be larger than floor(M/2).
+template <typename T, T M = 0>
+struct AscendingSeqNumComp
+ : private internal::SeqNumComp<T, std::integral_constant<T, M>> {
+ bool operator()(T a, T b) const {
+ return internal::SeqNumComp<T, std::integral_constant<T, M>>::operator()(a,
+ b);
+ }
+};
+
+// Comparator used to compare sequence numbers in a continuous fashion.
+//
+// WARNING! If used to sort sequence numbers of length M then the interval
+// covered by the sequence numbers may not be larger than floor(M/2).
+template <typename T, T M = 0>
+struct DescendingSeqNumComp
+ : private internal::SeqNumComp<T, std::integral_constant<T, M>> {
+ bool operator()(T a, T b) const {
+ return internal::SeqNumComp<T, std::integral_constant<T, M>>::operator()(b,
+ a);
+ }
+};
+
+} // namespace webrtc
+
+#endif // WEBRTC_MODULES_VIDEO_CODING_SEQUENCE_NUMBER_UTIL_H_