Method performDecode

src/Encoder/Base32.js:166–220

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

(content)

   * @return {number[]|string|Uint8Array|Chain|Promise} Decoded content
   */
  performDecode (content) {
    const { alphabet, decodeMap, padding, decodeContentFilter } =
      this.getVariantOptions()

    // Apply variant filter before decoding
    if (decodeContentFilter === 'uppercase') {
      content = content.toUpperCase()
    }

    // Add alphabet characters to decode map
    for (let i = 0; i < alphabet.getLength(); i++) {
      decodeMap[alphabet.getCodePointAt(i)] = i
    }

    // Prepare input and output arrays
    const input = content.getCodePoints()
    const inputLength = input.length
    const resultSize = Math.ceil(inputLength / 8) * 5
    const result = new Uint8Array(resultSize)
    let j = 0

    let shift = 8
    let carry = 0
    let codePoint, index

    // Go through every input code point
    for (let i = 0; i < inputLength; i++) {
      codePoint = input[i]

      if (codePoint === padding) {
        // Ignore padding
      } else if (decodeMap[codePoint] === undefined) {
        // Unexpected code point not being part of the alphabet or map
        throw new InvalidInputError(`Unexpected code point at index ${i}`)
      } else {
        // Decode character
        index = decodeMap[codePoint] & 0xff
        shift -= 5
        if (shift > 0) {
          carry |= index << shift
        } else if (shift < 0) {
          result[j++] = carry | (index >> -shift)
          shift += 8
          carry = (index << shift) & 0xff
        } else {
          result[j++] = carry | index
          shift = 8
          carry = 0
        }
      }
    }

    // Slice result to remove padding
    return result.slice(0, j)
  }

  /**
   * Triggered when a setting field has changed.