Add Iterable bitset class.

src/common/BitSetIterator.h

+//
+// Copyright 2015 The ANGLE 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.
+//
+// BitSetIterator:
+//   A helper class to quickly bitscan bitsets for set bits.
+//
+
+#ifndef COMMON_BITSETITERATOR_H_
+#define COMMON_BITSETITERATOR_H_
+
+#include <stdint.h>
+
+#include <bitset>
+
+#include "common/angleutils.h"
+#include "common/platform.h"
+
+namespace angle
+{
+template <size_t N>
+class BitSetIterator final
+{
+  public:
+    BitSetIterator(const std::bitset<N> &bitset);
+    BitSetIterator(const BitSetIterator &other);
+
+    class Iterator final
+    {
+      public:
+        Iterator(const std::bitset<N> *bits);
+        Iterator &operator++();
+
+        bool operator!=(const Iterator &other) const { return mBits != other.mBits; }
+        size_t operator*() const { return mCurrentBit; }
+        size_t getNextBit() const;
+
+      private:
+        unsigned long long mBits;
+        size_t mCurrentBit;
+    };
+
+    Iterator begin() const { return Iterator(&mBits); }
+    Iterator end() const { return Iterator(nullptr); }
+
+  private:
+    const std::bitset<N> &mBits;
+};
+
+template <size_t N>
+BitSetIterator<N>::BitSetIterator(const std::bitset<N> &bitset)
+    : mBits(bitset)
+{
+    static_assert(N <= 64, "IterableBitSet only supports up to 64 bits.");
+}
+
+template <size_t N>
+BitSetIterator<N>::BitSetIterator(const BitSetIterator &other)
+    : mBits(other.mBits)
+{
+}
+
+template <size_t N>
+BitSetIterator<N>::Iterator::Iterator(const std::bitset<N> *bits)
+    : mBits(bits ? bits->to_ullong() : 0ull), mCurrentBit(bits ? getNextBit() : 0ull)
+{
+}
+
+template <size_t N>
+typename BitSetIterator<N>::Iterator &BitSetIterator<N>::Iterator::operator++()
+{
+    mBits &= ~(1ull << mCurrentBit);
+    mCurrentBit = getNextBit();
+    return *this;
+}
+
+template <size_t N>
+size_t BitSetIterator<N>::Iterator::getNextBit() const
+{
+#if defined(_WIN64)
+    static_assert(sizeof(uint64_t) == sizeof(unsigned long long), "Incompatible sizes");
+
+    unsigned long firstBitIndex = 0ul;
+    unsigned char ret           = _BitScanForward64(&firstBitIndex, mBits);
+
+    if (ret != 0)
+        return static_cast<size_t>(firstBitIndex);
+#elif defined(_WIN32)
+    static_assert(sizeof(size_t) == sizeof(unsigned long), "Incompatible sizes");
+
+    unsigned long firstBitIndex     = 0ul;
+    const unsigned long BitsPerWord = 32ul;
+
+    for (unsigned long offset = 0; offset <= BitsPerWord; offset += BitsPerWord)
+    {
+        unsigned long wordBits = mBits >> offset;
+        unsigned char ret      = _BitScanForward(&firstBitIndex, wordBits);
+
+        if (ret != 0)
+        {
+            return static_cast<size_t>(firstBitIndex + offset);
+        }
+    }
+#elif defined(ANGLE_PLATFORM_LINUX) || defined(ANGLE_PLATFORM_APPLE)
+    if (mBits != 0)
+    {
+        return __builtin_ctzll(mBits);
+    }
+#else
+#error Please implement bit-scan-forward for your platform!
+#endif
+    return 0;
+}
+
+// Helper to avoid needing to specify the template parameter size
+template <size_t N>
+BitSetIterator<N> IterateBitSet(const std::bitset<N> &bitset)
+{
+    return BitSetIterator<N>(bitset);
+}
+
+}  // angle
+
+#endif // COMMON_BITSETITERATOR_H_

src/common/BitSetIterator_unittest.cpp

+//
+// Copyright 2015 The ANGLE 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.
+//
+// BitSetIteratorTest:
+//   Test the IterableBitSet class.
+//
+
+#include <gtest/gtest.h>
+
+#include "common/BitSetIterator.h"
+
+using namespace angle;
+
+namespace
+{
+class BitSetIteratorTest : public testing::Test
+{
+  protected:
+    std::bitset<40> mStateBits;
+};
+
+TEST_F(BitSetIteratorTest, Iterator)
+{
+    std::set<size_t> originalValues;
+    originalValues.insert(2);
+    originalValues.insert(6);
+    originalValues.insert(8);
+    originalValues.insert(35);
+
+    for (size_t value : originalValues)
+    {
+        mStateBits.set(value);
+    }
+
+    std::set<size_t> readValues;
+    for (size_t bit : IterateBitSet(mStateBits))
+    {
+        EXPECT_EQ(1u, originalValues.count(bit));
+        EXPECT_EQ(0u, readValues.count(bit));
+        readValues.insert(bit);
+    }
+
+    EXPECT_EQ(originalValues.size(), readValues.size());
+}
+
+}  // anonymous namespace

src/libGLESv2.gypi

@@ -8,6 +8,7 @@
         # These file lists are shared with the GN build.
         'libangle_common_sources':
         [
+            'common/BitSetIterator.h',
             'common/Float16ToFloat32.cpp',
             'common/MemoryBuffer.cpp',
             'common/MemoryBuffer.h',

src/tests/angle_unittests.gypi

@@ -15,6 +15,7 @@
         # This file list will be shared with the GN build.
         'angle_unittests_sources':
         [
+            '<(angle_path)/src/common/BitSetIterator_unittest.cpp',
             '<(angle_path)/src/common/Optional_unittest.cpp',
             '<(angle_path)/src/common/mathutil_unittest.cpp',
             '<(angle_path)/src/common/matrix_utils_unittest.cpp',