text: //= ===============================================================
  // SHA256.js
  //
  // Module that replicates the SHA-256 Cryptographic Hash
  // function in Javascript.
  //= ===============================================================
  
  // main variables
  const CHAR_SIZE = 8
  
  const K = [
    0x428a2f98, 0x71374491, 0xb5c0fbcf, 0xe9b5dba5, 0x3956c25b, 0x59f111f1,
    0x923f82a4, 0xab1c5ed5, 0xd807aa98, 0x12835b01, 0x243185be, 0x550c7dc3,
    0x72be5d74, 0x80deb1fe, 0x9bdc06a7, 0xc19bf174, 0xe49b69c1, 0xefbe4786,
    0x0fc19dc6, 0x240ca1cc, 0x2de92c6f, 0x4a7484aa, 0x5cb0a9dc, 0x76f988da,
    0x983e5152, 0xa831c66d, 0xb00327c8, 0xbf597fc7, 0xc6e00bf3, 0xd5a79147,
    0x06ca6351, 0x14292967, 0x27b70a85, 0x2e1b2138, 0x4d2c6dfc, 0x53380d13,
    0x650a7354, 0x766a0abb, 0x81c2c92e, 0x92722c85, 0xa2bfe8a1, 0xa81a664b,
    0xc24b8b70, 0xc76c51a3, 0xd192e819, 0xd6990624, 0xf40e3585, 0x106aa070,
    0x19a4c116, 0x1e376c08, 0x2748774c, 0x34b0bcb5, 0x391c0cb3, 0x4ed8aa4a,
    0x5b9cca4f, 0x682e6ff3, 0x748f82ee, 0x78a5636f, 0x84c87814, 0x8cc70208,
    0x90befffa, 0xa4506ceb, 0xbef9a3f7, 0xc67178f2
  ]
  
  /**
   * Adds padding to binary/hex string represention
   *
   * @param {string} str - string represention (binary/hex)
   * @param {int} bits - total number of bits wanted
   * @return {string} - string represention padding with empty (0) bits
   *
   * @example
   *      pad("10011", 8); // "00010011"
   */
  function pad(str, bits) {
    let res = str
    while (res.length % bits !== 0) {
      res = '0' + res
    }
    return res
  }
  
  /**
   * Separates string into chunks of the same size
   *
   * @param {string} str - string to separate into chunks
   * @param {int} size - number of characters wanted in each chunk
   * @return {array} - array of original string split into chunks
   *
   * @example
   *      chunkify("this is a test", 2); // ["th", "is", " i", "s ", "a ", "te", "st"]
   */
  function chunkify(str, size) {
    const chunks = []
    for (let i = 0; i < str.length; i += size) {
      chunks.push(str.slice(i, i + size))
    }
    return chunks
  }
  
  /**
   * Rotates string represention of bits to th left
   *
   * @param {string} bits - string representation of bits
   * @param {int} turns - number of rotations to make
   * @return {string} - string representation of bits after rotation
   *
   * @example
   *      rotateLeft("1011", 3); // "1101"
   */
  function rotateRight(bits, turns) {
    return bits.substr(bits.length - turns) + bits.substr(0, bits.length - turns)
  }
  
  /**
   * Pre-processes message to feed the algorithm loop
   *
   * @param {string} message - message to pre-process
   * @return {string} - processed message
   */
  function preProcess(message) {
    // covert message to binary representation padded to
    // 8 bits, and add 1
    let m =
      message
        .split('')
        .map((e) => e.charCodeAt(0))
        .map((e) => e.toString(2))
        .map((e) => pad(e, 8))
        .join('') + '1'
  
    // extend message by adding empty bits (0)
    while (m.length % 512 !== 448) {
      m += '0'
    }
  
    // length of message in binary, padded, and extended
    // to a 64 bit representation
    let ml = (message.length * CHAR_SIZE).toString(2)
    ml = pad(ml, 8)
    ml = '0'.repeat(64 - ml.length) + ml
  
    return m + ml
  }
  
  /**
   * Hashes message using SHA-256 Cryptographic Hash Function
   *
   * @param {string} message - message to hash
   * @return {string} - message digest (hash value)
   */
  function SHA256(message) {
    // initial hash variables
    let H0 = 0x6a09e667
    let H1 = 0xbb67ae85
    let H2 = 0x3c6ef372
    let H3 = 0xa54ff53a
    let H4 = 0x510e527f
    let H5 = 0x9b05688c
    let H6 = 0x1f83d9ab
    let H7 = 0x5be0cd19
  
    // pre-process message and split into 512 bit chunks
    const bits = preProcess(message)
    const chunks = chunkify(bits, 512)
  
    chunks.forEach(function (chunk, i) {
      // break each chunk into 16 32-bit words
      const words = chunkify(chunk, 32)
  
      // extend 16 32-bit words to 80 32-bit words
      for (let i = 16; i < 64; i++) {
        const W1 = words[i - 15]
        const W2 = words[i - 2]
        const R1 = rotateRight(W1, 7)
        const R2 = rotateRight(W1, 18)
        const R3 = rotateRight(W2, 17)
        const R4 = rotateRight(W2, 19)
        const S0 = parseInt(R1, 2) ^ parseInt(R2, 2) ^ (parseInt(W1, 2) >>> 3)
        const S1 = parseInt(R3, 2) ^ parseInt(R4, 2) ^ (parseInt(W2, 2) >>> 10)
        const val =
          parseInt(words[i - 16], 2) + S0 + parseInt(words[i - 7], 2) + S1
        words[i] = pad((val >>> 0).toString(2), 32)
      }
  
      // initialize variables for this chunk
      let [a, b, c, d, e, f, g, h] = [H0, H1, H2, H3, H4, H5, H6, H7]
  
      for (let i = 0; i < 64; i++) {
        const S1 =
          [6, 11, 25]
            .map((turns) => rotateRight(pad(e.toString(2), 32), turns))
            .map((bitstring) => parseInt(bitstring, 2))
            .reduce((acc, curr) => acc ^ curr, 0) >>> 0
        const CH = ((e & f) ^ (~e & g)) >>> 0
        const temp1 = (h + S1 + CH + K[i] + parseInt(words[i], 2)) >>> 0
        const S0 =
          [2, 13, 22]
            .map((turns) => rotateRight(pad(a.toString(2), 32), turns))
            .map((bitstring) => parseInt(bitstring, 2))
            .reduce((acc, curr) => acc ^ curr, 0) >>> 0
        const maj = ((a & b) ^ (a & c) ^ (b & c)) >>> 0
        const temp2 = (S0 + maj) >>> 0
  
        h = g
        g = f
        f = e
        e = (d + temp1) >>> 0
        d = c
        c = b
        b = a
        a = (temp1 + temp2) >>> 0
      }
  
      // add values for this chunk to main hash variables (unsigned)
      H0 = (H0 + a) >>> 0
      H1 = (H1 + b) >>> 0
      H2 = (H2 + c) >>> 0
      H3 = (H3 + d) >>> 0
      H4 = (H4 + e) >>> 0
      H5 = (H5 + f) >>> 0
      H6 = (H6 + g) >>> 0
      H7 = (H7 + h) >>> 0
    })
  
    // combine hash values of main hash variables and return
    const HH = [H0, H1, H2, H3, H4, H5, H6, H7]
      .map((e) => e.toString(16))
      .map((e) => pad(e, 8))
      .join('')
  
    return HH
  }
  
  // export SHA256 function
  module.exports = SHA256
  