Mpeg2 TS stream parser for media source.

media/mpeg2/mpeg2ts_crc.cc

+// Copyright (c) 2013 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "media/mpeg2/mpeg2ts_crc.h"
+
+namespace media {
+namespace mpeg2ts {
+
+Mpeg2TsCrc::Mpeg2TsCrc()
+    : crc_(0xffffffffu) {
+}
+
+void Mpeg2TsCrc::Update(uint32 data, int nbits) {
+  const uint32_t kCrcPoly = 0x4c11db7;

[acolwell GONE FROM CHROMIUM, 2013/09/05 18:29:10]

DCHECK_GT(nbits, 0);
DCHECK_LE(nbits, 32);

[damienv1, 2013/09/09 23:29:45]

Function signature changed: now always receive 8 bits of data at a time.

+
+  // Align the bits to the MSB.
+  data = data << (32 - nbits);
+
+  while (nbits > 0) {
+    if ((data ^ crc_) & 0x80000000) {
+      crc_ <<= 1;
+      crc_ ^= kCrcPoly;
+    } else {
+      crc_ <<= 1;
+    }
+
+    data <<= 1;
+    nbits--;
+  }
+}
+
+bool Mpeg2TsCrc::IsValid() {
+  return (crc_ == 0);
+}
+
+}  // namespace mpeg2ts
+}  // namespace media
+