text: // Copyright 2014 The Chromium Authors. All rights reserved.
  // Use of this source code is governed by a BSD-style license that can be
  // found in the LICENSE file.
  
  // SHA256 in javascript.
  //
  // SHA256 {
  //  SHA256();
  //  void reset();
  //  void update(byte[] data, opt_length);
  //  byte[32] digest();
  // }
  
  /** @constructor */
  function SHA256() {
    this._buf = new Array(64);
    this._W = new Array(64);
    this._pad = new Array(64);
    this._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
    ];
  
    this._pad[0] = 0x80;
    for (var i = 1; i < 64; ++i) {
      this._pad[i] = 0;
    }
  
    this.reset();
  }
  
  /** Reset the hasher */
  SHA256.prototype.reset = function() {
    this._chain = [
      0x6a09e667, 0xbb67ae85, 0x3c6ef372, 0xa54ff53a, 0x510e527f, 0x9b05688c,
      0x1f83d9ab, 0x5be0cd19
    ];
  
    this._inbuf = 0;
    this._total = 0;
  };
  
  /** Hash the next block of 64 bytes
   * @param {Array<number>} buf A 64 byte buffer
   */
  SHA256.prototype._compress = function(buf) {
    var W = this._W;
    var k = this._k;
  
    var _rotr = function(w, r) {
      return ((w << (32 - r)) | (w >>> r));
    };
  
    // get 16 big endian words
    for (var i = 0; i < 64; i += 4) {
      var w =
          (buf[i] << 24) | (buf[i + 1] << 16) | (buf[i + 2] << 8) | (buf[i + 3]);
      W[i / 4] = w;
    }
  
    // expand to 64 words
    for (var i = 16; i < 64; ++i) {
      var s0 = _rotr(W[i - 15], 7) ^ _rotr(W[i - 15], 18) ^ (W[i - 15] >>> 3);
      var s1 = _rotr(W[i - 2], 17) ^ _rotr(W[i - 2], 19) ^ (W[i - 2] >>> 10);
      W[i] = (W[i - 16] + s0 + W[i - 7] + s1) & 0xffffffff;
    }
  
    var A = this._chain[0];
    var B = this._chain[1];
    var C = this._chain[2];
    var D = this._chain[3];
    var E = this._chain[4];
    var F = this._chain[5];
    var G = this._chain[6];
    var H = this._chain[7];
  
    for (var i = 0; i < 64; ++i) {
      var S0 = _rotr(A, 2) ^ _rotr(A, 13) ^ _rotr(A, 22);
      var maj = (A & B) ^ (A & C) ^ (B & C);
      var t2 = (S0 + maj) & 0xffffffff;
      var S1 = _rotr(E, 6) ^ _rotr(E, 11) ^ _rotr(E, 25);
      var ch = (E & F) ^ ((~E) & G);
      var t1 = (H + S1 + ch + k[i] + W[i]) & 0xffffffff;
  
      H = G;
      G = F;
      F = E;
      E = (D + t1) & 0xffffffff;
      D = C;
      C = B;
      B = A;
      A = (t1 + t2) & 0xffffffff;
    }
  
    this._chain[0] += A;
    this._chain[1] += B;
    this._chain[2] += C;
    this._chain[3] += D;
    this._chain[4] += E;
    this._chain[5] += F;
    this._chain[6] += G;
    this._chain[7] += H;
  };
  
  /** Update the hash with additional data
   * @param {Array<number>|Uint8Array} bytes The data
   * @param {number=} opt_length How many bytes to hash, if not all */
  SHA256.prototype.update = function(bytes, opt_length) {
    if (!opt_length) {
      opt_length = bytes.length;
    }
  
    this._total += opt_length;
    for (var n = 0; n < opt_length; ++n) {
      this._buf[this._inbuf++] = bytes[n];
      if (this._inbuf == 64) {
        this._compress(this._buf);
        this._inbuf = 0;
      }
    }
  };
  
  /** Update the hash with a specified range from a data buffer
   * @param {Array<number>} bytes The data buffer
   * @param {number} start Starting index of the range in bytes
   * @param {number} end End index, will not be included in range
   */
  SHA256.prototype.updateRange = function(bytes, start, end) {
    this._total += (end - start);
    for (var n = start; n < end; ++n) {
      this._buf[this._inbuf++] = bytes[n];
      if (this._inbuf == 64) {
        this._compress(this._buf);
        this._inbuf = 0;
      }
    }
  };
  
  /**
   * Optionally update the hash with additional arguments, and return the
   * resulting hash value.
   * @param {...*} var_args Data buffers to hash
   * @return {!Array<number>} the SHA256 hash value.
   */
  SHA256.prototype.digest = function(var_args) {
    for (var i = 0; i < arguments.length; ++i) {
      this.update(arguments[i]);
    }
  
    var digest = new Array(32);
    var totalBits = this._total * 8;
  
    // add pad 0x80 0x00*
    if (this._inbuf < 56) {
      this.update(this._pad, 56 - this._inbuf);
    } else {
      this.update(this._pad, 64 - (this._inbuf - 56));
    }
  
    // add # bits, big endian
    for (var i = 63; i >= 56; --i) {
      this._buf[i] = totalBits & 255;
      totalBits >>>= 8;
    }
  
    this._compress(this._buf);
  
    var n = 0;
    for (var i = 0; i < 8; ++i) {
      for (var j = 24; j >= 0; j -= 8) {
        digest[n++] = (this._chain[i] >> j) & 255;
      }
    }
  
    return digest;
  };
  