1 files changed, 104 insertions, 0 deletions
diff --git a/dom/media/BitWriter.cpp b/dom/media/BitWriter.cpp
new file mode 100644
index 0000000000..e1d513f191
--- /dev/null
+++ b/dom/media/BitWriter.cpp
@@ -0,0 +1,104 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "BitWriter.h"
+
+#include <stdint.h>
+
+#include "MediaData.h"
+#include "mozilla/MathAlgorithms.h"
+
+namespace mozilla {
+
+constexpr uint8_t golombLen[256] = {
+    1,  3,  3,  5,  5,  5,  5,  7,  7,  7,  7,  7,  7,  7,  7,  9,  9,  9,  9,
+    9,  9,  9,  9,  9,  9,  9,  9,  9,  9,  9,  9,  11, 11, 11, 11, 11, 11, 11,
+    11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11,
+    11, 11, 11, 11, 11, 11, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13,
+    13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13,
+    13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13,
+    13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 15, 15, 15, 15, 15, 15,
+    15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,
+    15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,
+    15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,
+    15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,
+    15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,
+    15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,
+    15, 15, 15, 15, 15, 15, 15, 15, 17,
+};
+
+BitWriter::BitWriter(MediaByteBuffer* aBuffer) : mBuffer(aBuffer) {}
+
+BitWriter::~BitWriter() = default;
+
+void BitWriter::WriteBits(uint64_t aValue, size_t aBits) {
+  MOZ_ASSERT(aBits <= sizeof(uint64_t) * 8);
+
+  while (aBits) {
+    if (mBitIndex == 0) {
+      mBuffer->AppendElement(0);
+    }
+
+    const uint8_t clearMask = ~(~0u << (8 - mBitIndex));
+    uint8_t mask = 0;
+
+    if (mBitIndex + aBits > 8) {
+      // Not enough bits in the current byte to write all the bits
+      // required, we'll process what we can and continue with the left over.
+      const uint8_t leftOverBits = mBitIndex + aBits - 8;
+      const uint64_t leftOver = aValue & (~uint64_t(0) >> (8 - mBitIndex));
+      mask = aValue >> leftOverBits;
+
+      mBitIndex = 8;
+      aValue = leftOver;
+      aBits = leftOverBits;
+    } else {
+      const uint8_t offset = 8 - mBitIndex - aBits;
+      mask = aValue << offset;
+
+      mBitIndex += aBits;
+      aBits = 0;
+    }
+
+    mBuffer->ElementAt(mPosition) |= mask & clearMask;
+
+    if (mBitIndex == 8) {
+      mPosition++;
+      mBitIndex = 0;
+    }
+  }
+}
+
+void BitWriter::WriteUE(uint32_t aValue) {
+  MOZ_ASSERT(aValue <= (UINT32_MAX - 1));
+
+  if (aValue < 256) {
+    WriteBits(aValue + 1, golombLen[aValue]);
+  } else {
+    const uint32_t e = FloorLog2(aValue + 1);
+    WriteBits(aValue + 1, e * 2 + 1);
+  }
+}
+
+void BitWriter::WriteULEB128(uint64_t aValue) {
+  // See https://en.wikipedia.org/wiki/LEB128#Encode_unsigned_integer
+  do {
+    uint8_t byte = aValue & 0x7F;
+    aValue >>= 7;
+    WriteBit(aValue != 0);
+    WriteBits(byte, 7);
+  } while (aValue != 0);
+}
+
+void BitWriter::CloseWithRbspTrailing() {
+  WriteBit(true);
+  WriteBits(0, (8 - mBitIndex) & 7);
+}
+
+void BitWriter::AdvanceBytes(uint32_t aByteOffset) {
+  MOZ_DIAGNOSTIC_ASSERT(mBitIndex == 0);
+  mPosition += aByteOffset;
+}
+
+}  // namespace mozilla