qrcoder/src/qrmath.js

QRCoder is *a pure browser qrcode generation* which is standalone. It is based on a <a href='http://www.d-project.com/qrcode/index.html'>library</a> which build qrcode in various language.

const EXP_TABLE = new Array(256)
const LOG_TABLE = new Array(256)
// initialize tables
for (let i = 0; i < 8; i += 1) {
  EXP_TABLE[i] = 1 << i
}
for (let i = 8; i < 256; i += 1) {
  EXP_TABLE[i] = EXP_TABLE[i - 4] ^ EXP_TABLE[i - 5] ^
    EXP_TABLE[i - 6] ^ EXP_TABLE[i - 8]
}
for (let i = 0; i < 255; i += 1) {
  LOG_TABLE[EXP_TABLE[i]] = i
}

export const QRMath = {
  glog: function (n) {
    if (n < 1) {
      throw new Error('glog(' + n + ')')
    }

    return LOG_TABLE[n]
  },
  gexp: function (n) {
    while (n < 0) {
      n += 255
    }

    while (n >= 256) {
      n -= 255
    }

    return EXP_TABLE[n]
  }
}