Repo created

TMessagesProj/jni/voip/webrtc/rtc_base/crc32.cc

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+/*
+ *  Copyright 2012 The WebRTC 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 in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#include "rtc_base/crc32.h"
+
+#include "rtc_base/arraysize.h"
+
+namespace rtc {
+
+// This implementation is based on the sample implementation in RFC 1952.
+
+// CRC32 polynomial, in reversed form.
+// See RFC 1952, or http://en.wikipedia.org/wiki/Cyclic_redundancy_check
+static const uint32_t kCrc32Polynomial = 0xEDB88320;
+
+static uint32_t* LoadCrc32Table() {
+  static uint32_t kCrc32Table[256];
+  for (uint32_t i = 0; i < arraysize(kCrc32Table); ++i) {
+    uint32_t c = i;
+    for (size_t j = 0; j < 8; ++j) {
+      if (c & 1) {
+        c = kCrc32Polynomial ^ (c >> 1);
+      } else {
+        c >>= 1;
+      }
+    }
+    kCrc32Table[i] = c;
+  }
+  return kCrc32Table;
+}
+
+uint32_t UpdateCrc32(uint32_t start, const void* buf, size_t len) {
+  static uint32_t* kCrc32Table = LoadCrc32Table();
+
+  uint32_t c = start ^ 0xFFFFFFFF;
+  const uint8_t* u = static_cast<const uint8_t*>(buf);
+  for (size_t i = 0; i < len; ++i) {
+    c = kCrc32Table[(c ^ u[i]) & 0xFF] ^ (c >> 8);
+  }
+  return c ^ 0xFFFFFFFF;
+}
+
+}  // namespace rtc