Implemented a new sequence number unwrapper in sequence_number_util.h.
There is already an Unwrapper in webrtc/modules/include/module_common_types.h,
but we reimplemented it in sequence_number_util.h for a few reasons:
- Such a class belongs in sequence_number_util.h.
- It is a cleaner implementation since we can use the rest of
sequence_number_util.h functionality.
- You can choose at which number the unwrapped sequence should start,
which is used to avoid the edge case when a backward wrap can happen
as the first few numbers are unwrapped.
- This unwrapper can unwrap numbers that does not wrap 8/16/32 bits.
BUG=None
Review-Url: https://codereview.webrtc.org/2977603002
Cr-Commit-Position: refs/heads/master@{#19154}
diff --git a/webrtc/modules/video_coding/sequence_number_util.h b/webrtc/modules/video_coding/sequence_number_util.h
index 8a139a3..e3bc38e 100644
--- a/webrtc/modules/video_coding/sequence_number_util.h
+++ b/webrtc/modules/video_coding/sequence_number_util.h
@@ -15,6 +15,8 @@
#include <type_traits>
#include "webrtc/rtc_base/mod_ops.h"
+#include "webrtc/rtc_base/optional.h"
+#include "webrtc/rtc_base/safe_compare.h"
namespace webrtc {
@@ -24,7 +26,7 @@
// 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) {
+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;
@@ -33,8 +35,8 @@
return ForwardDiff<T, M>(b, a) <= maxDist;
}
-template <typename T>
-inline bool AheadOrAt(T a, T b) {
+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);
@@ -43,66 +45,76 @@
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>
+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);
}
-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>> {
+// 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); }
};
-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);
- }
+struct DescendingSeqNumComp {
+ bool operator()(T a, T b) const { return AheadOf<T, M>(b, a); }
};
-// 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).
+// 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>
-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);
+class SeqNumUnwrapper {
+ static_assert(
+ std::is_unsigned<T>::value &&
+ rtc::SafeLt(std::numeric_limits<T>::max(),
+ std::numeric_limits<uint64_t>::max()),
+ "Type unwrapped must be an unsigned integer smaller than uint64_t.");
+
+ public:
+ SeqNumUnwrapper() : last_unwrapped_(0) {}
+ 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