qrcode/lib/core/format-info.js

QRCode / 2d Barcode api with both server side and client side support using canvas

var Utils = require('./utils')

var G15 = (1 << 10) | (1 << 8) | (1 << 5) | (1 << 4) | (1 << 2) | (1 << 1) | (1 << 0)
var G15_MASK = (1 << 14) | (1 << 12) | (1 << 10) | (1 << 4) | (1 << 1)
var G15_BCH = Utils.getBCHDigit(G15)

/**
 * Returns format information with relative error correction bits
 *
 * The format information is a 15-bit sequence containing 5 data bits,
 * with 10 error correction bits calculated using the (15, 5) BCH code.
 *
 * @param  {Number} errorCorrectionLevel Error correction level
 * @param  {Number} mask                 Mask pattern
 * @return {Number}                      Encoded format information bits
 */
exports.getEncodedBits = function getEncodedBits (errorCorrectionLevel, mask) {
  var data = ((errorCorrectionLevel.bit << 3) | mask)
  var d = data << 10

  while (Utils.getBCHDigit(d) - G15_BCH >= 0) {
    d ^= (G15 << (Utils.getBCHDigit(d) - G15_BCH))
  }

  // xor final data with mask pattern in order to ensure that
  // no combination of Error Correction Level and data mask pattern
  // will result in an all-zero data string
  return ((data << 10) | d) ^ G15_MASK
}