JavaScript Base-40 Class

index.js

// based on https://github.com/blockstack/blockstack-core/blob/ff86948ed2f720824cd5e6ece6a63aaaf2bf81ff/blockstack/lib/b40.py
class B40 {
  constructor() {
    this.B16_CHARS = '0123456789abcdef'
    this.B40_CHARS = '0123456789abcdefghijklmnopqrstuvwxyz-_.+'
  }

  divmod(x, y) {
    const div = x / y
    const rem = x % y
    return [div, rem]
  }

  intToCharset(val, charset) {
    if (val < BigInt(0)) return
    if (val === BigInt(0)) return charset[0]
    let output = ''
    while (val > BigInt(0)) {
      let [newval, digit] = this.divmod(val, BigInt(charset.length))
      val = newval
      output += charset[digit]
    }
    return output
      .split('')
      .reverse()
      .join('')
  }

  charsetToInt(str, charset) {
    let output = BigInt(0)
    str.split('').forEach(function(char) {
      output = output * BigInt(charset.length) + BigInt(charset.indexOf(char))
    })
    return output
  }

  convertCharset(str, original, target) {
    let intermediate = this.charsetToInt(str, original)
    return this.intToCharset(intermediate, target)
  }

  hexPad(x) {
    return (x.length % 2) > 0 ? ('0' * (x.length % 2)) + x : x
  }
    
  charsetToHex(str, charset) {
    return this.hexPad(this.convertCharset(str, charset, this.B16_CHARS))
  }

  hexToCharset(str, charset) {
    return this.convertCharset(str, this.B16_CHARS, charset)
  }

  base40ToBin(str) {
    return Buffer.from(this.charsetToHex(str, this.B40_CHARS), 'hex')
  }

  binToBase40(buf) {
    return this.hexToCharset(buf.toString('hex'), this.B40_CHARS)
  }

  base40ToHex(str) {
    return this.base40ToBin(str).toString('hex')
  }
}

export default B40