chat-server/qq-imsvr/node_modules/crc/lib/crc16_xmodem.js

'use strict';

var _buffer = require('buffer');

var _define_crc = require('./define_crc');

var _define_crc2 = _interopRequireDefault(_define_crc);

function _interopRequireDefault(obj) { return obj && obj.__esModule ? obj : { default: obj }; }

module.exports = (0, _define_crc2.default)('xmodem', function (buf, previous) {
  if (!_buffer.Buffer.isBuffer(buf)) buf = (0, _buffer.Buffer)(buf);

  var crc = typeof previous !== 'undefined' ? ~ ~previous : 0x0;

  for (var index = 0; index < buf.length; index++) {
    var byte = buf[index];
    var code = crc >>> 8 & 0xFF;

    code ^= byte & 0xFF;
    code ^= code >>> 4;
    crc = crc << 8 & 0xFFFF;
    crc ^= code;
    code = code << 5 & 0xFFFF;
    crc ^= code;
    code = code << 7 & 0xFFFF;
    crc ^= code;
  }

  return crc;
});