Move sequence_number_utils.h to rtc_base/
Bug: webrtc:8440
Change-Id: I36e70da6ce70b95db7d3fce8b0013bff5c795bfc
Reviewed-on: https://webrtc-review.googlesource.com/14860
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Reviewed-by: Åsa Persson <asapersson@webrtc.org>
Reviewed-by: Philip Eliasson <philipel@webrtc.org>
Commit-Queue: Björn Terelius <terelius@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#20429}diff --git a/rtc_base/numerics/sequence_number_util.h b/rtc_base/numerics/sequence_number_util.h
new file mode 100644
index 0000000..9dbd812
--- /dev/null
+++ b/rtc_base/numerics/sequence_number_util.h
@@ -0,0 +1,128 @@
+/*
+ * 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 RTC_BASE_NUMERICS_SEQUENCE_NUMBER_UTIL_H_
+#define RTC_BASE_NUMERICS_SEQUENCE_NUMBER_UTIL_H_
+
+#include <limits>
+#include <type_traits>
+
+#include "api/optional.h"
+#include "rtc_base/mod_ops.h"
+#include "rtc_base/safe_compare.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 typename std::enable_if<(M > 0), bool>::type 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, T M>
+inline typename std::enable_if<(M == 0), bool>::type 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;
+}
+
+template <typename T>
+inline bool AheadOrAt(T a, T b) {
+ return AheadOrAt<T, 0>(a, b);
+}
+
+// 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 = 0>
+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);
+}
+
+// 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 {
+ bool operator()(T a, T b) const { return AheadOf<T, M>(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 {
+ bool operator()(T a, T b) const { return AheadOf<T, M>(b, a); }
+};
+
+// A sequencer number unwrapper where the start value of the unwrapped sequence
+// can be set. The unwrapped value is not allowed to wrap.
+template <typename T, T M = 0>
+class SeqNumUnwrapper {
+ // Use '<' instead of rtc::SafeLt to avoid crbug.com/753488
+ static_assert(
+ std::is_unsigned<T>::value &&
+ std::numeric_limits<T>::max() < std::numeric_limits<uint64_t>::max(),
+ "Type unwrapped must be an unsigned integer smaller than uint64_t.");
+
+ public:
+ // We want a default value that is close to 2^62 for a two reasons. Firstly,
+ // we can unwrap wrapping numbers in either direction, and secondly, the
+ // unwrapped numbers can be stored in either int64_t or uint64_t. We also want
+ // the default value to be human readable, which makes a power of 10 suitable.
+ static constexpr uint64_t kDefaultStartValue = 1000000000000000000UL;
+
+ SeqNumUnwrapper() : last_unwrapped_(kDefaultStartValue) {}
+ explicit SeqNumUnwrapper(uint64_t start_at) : last_unwrapped_(start_at) {}
+
+ uint64_t Unwrap(T value) {
+ if (!last_value_)
+ last_value_.emplace(value);
+
+ uint64_t unwrapped = 0;
+ if (AheadOrAt<T, M>(value, *last_value_)) {
+ unwrapped = last_unwrapped_ + ForwardDiff<T, M>(*last_value_, value);
+ RTC_CHECK_GE(unwrapped, last_unwrapped_);
+ } else {
+ unwrapped = last_unwrapped_ - ReverseDiff<T, M>(*last_value_, value);
+ RTC_CHECK_LT(unwrapped, last_unwrapped_);
+ }
+
+ *last_value_ = value;
+ last_unwrapped_ = unwrapped;
+ return last_unwrapped_;
+ }
+
+ private:
+ uint64_t last_unwrapped_;
+ rtc::Optional<T> last_value_;
+};
+
+} // namespace webrtc
+
+#endif // RTC_BASE_NUMERICS_SEQUENCE_NUMBER_UTIL_H_