Method performEncode

src/Encoder/Ascii85.js:63–112

* Performs encode on given content. * @protected * @param {Chain} content * @return {number[]|string|Uint8Array|Chain|Promise} Encoded content

(content)

   * @return {number[]|string|Uint8Array|Chain|Promise} Encoded content
   */
  performEncode (content) {
    const bytes = content.getBytes()
    const variant = variantSpecs.find(variant =>
      variant.name === this.getSettingValue('variant'))
    const n = bytes.length

    // Encode each tuple of 4 bytes
    let string = ''
    let digits, j, tuple
    for (let i = 0; i < n; i += 4) {
      // Read 32-bit unsigned integer from bytes following the
      // big-endian convention (most significant byte first)
      tuple = (
        ((bytes[i]) << 24) +
        ((bytes[i + 1] || 0) << 16) +
        ((bytes[i + 2] || 0) << 8) +
        ((bytes[i + 3] || 0))
      ) >>> 0

      if (variant.zeroTupleChar === null || tuple > 0) {
        // Calculate 5 digits by repeatedly dividing
        // by 85 and taking the remainder
        digits = []
        for (j = 0; j < 5; j++) {
          digits.push(tuple % 85)
          tuple = Math.floor(tuple / 85)
        }

        // Take most significant digit first
        digits = digits.reverse()

        if (n < i + 4) {
          // Omit final characters added due to bytes of padding
          digits.splice(n - (i + 4), 4)
        }

        // Convert digits to characters and glue them together
        string += digits.map(digit =>
          variant.alphabet === null
            ? String.fromCharCode(digit + 33)
            : variant.alphabet[digit]
        ).join('')
      } else {
        // An all-zero tuple is encoded as a single character
        string += variant.zeroTupleChar
      }
    }

    return string
  }

  /**
   * Triggered before performing decode on given content.