From e2c548503beb7d5398acd537dc4cab2d3c4775f7 Mon Sep 17 00:00:00 2001
From: Alessio Bazzica <alessiob@webrtc.org>
Date: Tue, 20 Oct 2020 17:24:55 +0200
Subject: [PATCH] rtc::ArrayView reverse iterators

- rtc::ArrayView::rbegin()
- rtc::ArrayView::rend()
- rtc::ArrayView::crbegin()
- rtc::ArrayView::crend()

Bug: webrtc:7494
Change-Id: Id773d66cc9da8bd58def1dba35a706914440ef37
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/189880
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Commit-Queue: Alessio Bazzica <alessiob@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#32458}
---
 api/array_view.h           | 13 ++++++++++
 api/array_view_unittest.cc | 52 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 65 insertions(+)

diff --git a/api/array_view.h b/api/array_view.h
index a66369a3d3..df365cb740 100644
--- a/api/array_view.h
+++ b/api/array_view.h
@@ -13,6 +13,7 @@
 
 #include <algorithm>
 #include <array>
+#include <iterator>
 #include <type_traits>
 
 #include "rtc_base/checks.h"
@@ -258,6 +259,18 @@ class ArrayView final : public impl::ArrayViewBase<T, Size> {
   T* end() const { return this->data() + this->size(); }
   const T* cbegin() const { return this->data(); }
   const T* cend() const { return this->data() + this->size(); }
+  std::reverse_iterator<T*> rbegin() const {
+    return std::make_reverse_iterator(end());
+  }
+  std::reverse_iterator<T*> rend() const {
+    return std::make_reverse_iterator(begin());
+  }
+  std::reverse_iterator<const T*> crbegin() const {
+    return std::make_reverse_iterator(cend());
+  }
+  std::reverse_iterator<const T*> crend() const {
+    return std::make_reverse_iterator(cbegin());
+  }
 
   ArrayView<T> subview(size_t offset, size_t size) const {
     return offset < this->size()
diff --git a/api/array_view_unittest.cc b/api/array_view_unittest.cc
index 0357f68aa2..97267df006 100644
--- a/api/array_view_unittest.cc
+++ b/api/array_view_unittest.cc
@@ -451,6 +451,20 @@ TEST(ArrayViewTest, TestIterationEmpty) {
   }
 }
 
+TEST(ArrayViewTest, TestReverseIterationEmpty) {
+  // Variable-size.
+  ArrayView<std::vector<std::vector<std::vector<std::string>>>> av;
+  EXPECT_EQ(av.rbegin(), av.rend());
+  EXPECT_EQ(av.crbegin(), av.crend());
+  EXPECT_TRUE(av.empty());
+
+  // Fixed-size.
+  ArrayView<std::vector<std::vector<std::vector<std::string>>>, 0> af;
+  EXPECT_EQ(af.begin(), af.end());
+  EXPECT_EQ(af.cbegin(), af.cend());
+  EXPECT_TRUE(af.empty());
+}
+
 TEST(ArrayViewTest, TestIterationVariable) {
   char arr[] = "Arrr!";
   ArrayView<char> av(arr);
@@ -472,6 +486,25 @@ TEST(ArrayViewTest, TestIterationVariable) {
   }
 }
 
+TEST(ArrayViewTest, TestReverseIterationVariable) {
+  char arr[] = "Arrr!";
+  ArrayView<char> av(arr);
+  EXPECT_EQ('\0', *av.rbegin());
+  EXPECT_EQ('\0', *av.crbegin());
+  EXPECT_EQ('A', *(av.rend() - 1));
+  EXPECT_EQ('A', *(av.crend() - 1));
+
+  const char* cit = av.cend() - 1;
+  for (auto crit = av.crbegin(); crit != av.crend(); ++crit, --cit) {
+    EXPECT_EQ(*cit, *crit);
+  }
+
+  char* it = av.end() - 1;
+  for (auto rit = av.rbegin(); rit != av.rend(); ++rit, --it) {
+    EXPECT_EQ(*it, *rit);
+  }
+}
+
 TEST(ArrayViewTest, TestIterationFixed) {
   char arr[] = "Arrr!";
   ArrayView<char, 6> av(arr);
@@ -493,6 +526,25 @@ TEST(ArrayViewTest, TestIterationFixed) {
   }
 }
 
+TEST(ArrayViewTest, TestReverseIterationFixed) {
+  char arr[] = "Arrr!";
+  ArrayView<char, 6> av(arr);
+  EXPECT_EQ('\0', *av.rbegin());
+  EXPECT_EQ('\0', *av.crbegin());
+  EXPECT_EQ('A', *(av.rend() - 1));
+  EXPECT_EQ('A', *(av.crend() - 1));
+
+  const char* cit = av.cend() - 1;
+  for (auto crit = av.crbegin(); crit != av.crend(); ++crit, --cit) {
+    EXPECT_EQ(*cit, *crit);
+  }
+
+  char* it = av.end() - 1;
+  for (auto rit = av.rbegin(); rit != av.rend(); ++rit, --it) {
+    EXPECT_EQ(*it, *rit);
+  }
+}
+
 TEST(ArrayViewTest, TestEmpty) {
   EXPECT_TRUE(ArrayView<int>().empty());
   const int a[] = {1, 2, 3};