// Protocol Buffers - Google's data interchange format
// Copyright 2008 Google Inc.  All rights reserved.
// https://developers.google.com/protocol-buffers/
//
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// modification, are permitted provided that the following conditions are
// met:
//
//     * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
//     * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following disclaimer
// in the documentation and/or other materials provided with the
// distribution.
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// contributors may be used to endorse or promote products derived from
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package com.google.protobuf;

/** Common methods and constants for the binary protobuf protocol. */
@ExperimentalApi
final class BinaryProtocolUtil {
  private BinaryProtocolUtil() {}

  private static final int TAG_TYPE_BITS = 3;
  private static final int TAG_TYPE_MASK = (1 << TAG_TYPE_BITS) - 1;

  static final byte WIRETYPE_VARINT = 0;
  static final byte WIRETYPE_FIXED64 = 1;
  static final byte WIRETYPE_LENGTH_DELIMITED = 2;
  static final byte WIRETYPE_START_GROUP = 3;
  static final byte WIRETYPE_END_GROUP = 4;
  static final byte WIRETYPE_FIXED32 = 5;
  static final byte MAX_VARINT32_SIZE = 5;
  static final byte MAX_VARINT64_SIZE = 10;
  static final byte FIXED32_SIZE = 4;
  static final byte FIXED64_SIZE = 8;

  static int tagFor(int fieldNumber, byte wireType) {
    return (fieldNumber << TAG_TYPE_BITS) | wireType;
  }

  static int getFieldNumber(final int tag) {
    return tag >>> TAG_TYPE_BITS;
  }

  static int getWireType(final int tag) {
    return tag & TAG_TYPE_MASK;
  }

  /**
   * Decode a ZigZag-encoded 32-bit value. ZigZag encodes signed integers into values that can be
   * efficiently encoded with varint. (Otherwise, negative values must be sign-extended to 64 bits
   * to be varint encoded, thus always taking 10 bytes on the wire.)
   *
   * @param n An unsigned 32-bit integer, stored in a signed int because Java has no explicit
   *     unsigned support.
   * @return A signed 32-bit integer.
   */
  static int decodeZigZag32(final int n) {
    return (n >>> 1) ^ -(n & 1);
  }

  /**
   * Decode a ZigZag-encoded 64-bit value. ZigZag encodes signed integers into values that can be
   * efficiently encoded with varint. (Otherwise, negative values must be sign-extended to 64 bits
   * to be varint encoded, thus always taking 10 bytes on the wire.)
   *
   * @param n An unsigned 64-bit integer, stored in a signed int because Java has no explicit
   *     unsigned support.
   * @return A signed 64-bit integer.
   */
  static long decodeZigZag64(final long n) {
    return (n >>> 1) ^ -(n & 1);
  }

  /**
   * Encode a ZigZag-encoded 32-bit value. ZigZag encodes signed integers into values that can be
   * efficiently encoded with varint. (Otherwise, negative values must be sign-extended to 64 bits
   * to be varint encoded, thus always taking 10 bytes on the wire.)
   *
   * @param n A signed 32-bit integer.
   * @return An unsigned 32-bit integer, stored in a signed int because Java has no explicit
   *     unsigned support.
   */
  static int encodeZigZag32(final int n) {
    // Note:  the right-shift must be arithmetic
    return (n << 1) ^ (n >> 31);
  }

  /**
   * Encode a ZigZag-encoded 64-bit value. ZigZag encodes signed integers into values that can be
   * efficiently encoded with varint. (Otherwise, negative values must be sign-extended to 64 bits
   * to be varint encoded, thus always taking 10 bytes on the wire.)
   *
   * @param n A signed 64-bit integer.
   * @return An unsigned 64-bit integer, stored in a signed int because Java has no explicit
   *     unsigned support.
   */
  static long encodeZigZag64(final long n) {
    // Note:  the right-shift must be arithmetic
    return (n << 1) ^ (n >> 63);
  }
}