From 8ab87e41a19c4bf9ccb8300a29f707ee07c9ad33 Mon Sep 17 00:00:00 2001
From: philipel <philipel@webrtc.org>
Date: Mon, 19 Jul 2021 15:40:17 +0200
Subject: [PATCH] Add UnwrapForward and UnwrapBackwards to SeqNumUnwrapper.

Bug: webrtc:12979
Change-Id: I4c3b3f5e1ff70ae528cfd73a34baafc75cccf481
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/226462
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Commit-Queue: Philip Eliasson <philipel@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#34505}
---
 rtc_base/numerics/sequence_number_util.h      | 22 +++++++++++++++
 .../numerics/sequence_number_util_unittest.cc | 28 +++++++++++++++++++
 2 files changed, 50 insertions(+)

diff --git a/rtc_base/numerics/sequence_number_util.h b/rtc_base/numerics/sequence_number_util.h
index 96a4974ec5..5b4ad10e94 100644
--- a/rtc_base/numerics/sequence_number_util.h
+++ b/rtc_base/numerics/sequence_number_util.h
@@ -109,6 +109,28 @@ class SeqNumUnwrapper {
     return last_unwrapped_;
   }
 
+  int64_t UnwrapForward(T value) {
+    if (!last_value_) {
+      last_unwrapped_ = {value};
+    } else {
+      last_unwrapped_ += ForwardDiff<T, M>(*last_value_, value);
+    }
+
+    last_value_ = value;
+    return last_unwrapped_;
+  }
+
+  int64_t UnwrapBackwards(T value) {
+    if (!last_value_) {
+      last_unwrapped_ = {value};
+    } else {
+      last_unwrapped_ -= ReverseDiff<T, M>(*last_value_, value);
+    }
+
+    last_value_ = value;
+    return last_unwrapped_;
+  }
+
  private:
   int64_t last_unwrapped_ = 0;
   absl::optional<T> last_value_;
diff --git a/rtc_base/numerics/sequence_number_util_unittest.cc b/rtc_base/numerics/sequence_number_util_unittest.cc
index d7fa0b1467..c353c921fa 100644
--- a/rtc_base/numerics/sequence_number_util_unittest.cc
+++ b/rtc_base/numerics/sequence_number_util_unittest.cc
@@ -303,4 +303,32 @@ TEST(SeqNumUnwrapper, ManyBackwardWraps) {
   }
 }
 
+TEST(SeqNumUnwrapper, UnwrapForward) {
+  SeqNumUnwrapper<uint8_t> unwrapper;
+  EXPECT_EQ(255, unwrapper.Unwrap(255));
+  EXPECT_EQ(256, unwrapper.UnwrapForward(0));
+  EXPECT_EQ(511, unwrapper.UnwrapForward(255));
+}
+
+TEST(SeqNumUnwrapper, UnwrapForwardWithDivisor) {
+  SeqNumUnwrapper<uint8_t, 33> unwrapper;
+  EXPECT_EQ(30, unwrapper.UnwrapForward(30));
+  EXPECT_EQ(36, unwrapper.UnwrapForward(3));
+  EXPECT_EQ(63, unwrapper.UnwrapForward(30));
+}
+
+TEST(SeqNumUnwrapper, UnwrapBackwards) {
+  SeqNumUnwrapper<uint8_t> unwrapper;
+  EXPECT_EQ(0, unwrapper.UnwrapBackwards(0));
+  EXPECT_EQ(-2, unwrapper.UnwrapBackwards(254));
+  EXPECT_EQ(-256, unwrapper.UnwrapBackwards(0));
+}
+
+TEST(SeqNumUnwrapper, UnwrapBackwardsWithDivisor) {
+  SeqNumUnwrapper<uint8_t, 33> unwrapper;
+  EXPECT_EQ(0, unwrapper.Unwrap(0));
+  EXPECT_EQ(-2, unwrapper.UnwrapBackwards(31));
+  EXPECT_EQ(-33, unwrapper.UnwrapBackwards(0));
+}
+
 }  // namespace webrtc