function sha1Hash(msg) {
  var i, t;
  // constants [¤4.2.1]
  var K = [0x5a827999, 0x6ed9eba1, 0x8f1bbcdc, 0xca62c1d6];
  // PREPROCESSING
  // add trailing '1' bit to string [¤5.1.1]
  msg += String.fromCharCode(0x80);
  // convert string msg into 512-bit/16-integer
  // blocks arrays of ints [¤5.2.1]
  // long enough to contain msg plus 2-word length
  var l = Math.ceil(msg.length / 4) + 2;
  // in N 16-int blocks
  var N = Math.ceil(l / 16);
  var M = new Array(N);
  for (i = 0; i < N; i++) {
    M[i] = new Array(16);
    // encode 4 chars per integer, big-endian encoding
    for (var j = 0; j < 16; j++) {
      M[i][j] =
          (msg.charCodeAt(i * 64 + j * 4) << 24) | (msg.charCodeAt(i * 64 + j * 4 + 1) << 16) |
              (msg.charCodeAt(i * 64 + j * 4 + 2) << 8) | (msg.charCodeAt(i * 64 + j * 4 + 3));
    }
  }
  // add length (in bits) into final pair of 32-bit integers
  // (big-endian) [5.1.1]
  // note: most significant word would be
  // ((len-1)*8 >>> 32, but since JS converts
  // bitwise-op args to 32 bits, we need to simulate
  // this by arithmetic operators
  M[N - 1][14] = ((msg.length - 1) * 8) / Math.pow(2, 32);
  M[N - 1][14] = Math.floor(M[N - 1][14]);
  M[N - 1][15] = ((msg.length - 1) * 8) & 0xffffffff;
  // set initial hash value [¤5.3.1]
  var H0 = 0x67452301;
  var H1 = 0xefcdab89;
  var H2 = 0x98badcfe;
  var H3 = 0x10325476;
  var H4 = 0xc3d2e1f0;
  // HASH COMPUTATION [¤6.1.2]
  var W = new Array(80);
  var a, b, c, d, e;
  for (i = 0; i < N; i++) {
    // 1 - prepare message schedule 'W'
    for (t = 0; t < 16; t++) {
      W[t] = M[i][t];
    }
    for (t = 16; t < 80; t++) {
      W[t] = ROTL(W[t - 3] ^ W[t - 8] ^ W[t - 14] ^ W[t - 16], 1);
    }
    // 2 - initialise five working variables
    // a, b, c, d, e with previous hash value
    a = H0;
    b = H1;
    c = H2;
    d = H3;
    e = H4;
    // 3 - main loop
    for (t = 0; t < 80; t++) {
      // seq for blocks of 'f' functions and 'K' constants
      var s = Math.floor(t / 20);
      var T = (ROTL(a, 5) + f(s, b, c, d) + e + K[s] + W[t]) & 0xffffffff;
      e = d;
      d = c;
      c = ROTL(b, 30);
      b = a;
      a = T;
    }
    // 4 - compute the new intermediate hash value
    // note 'addition modulo 2^32'
    H0 = (H0 + a) & 0xffffffff;
    H1 = (H1 + b) & 0xffffffff;
    H2 = (H2 + c) & 0xffffffff;
    H3 = (H3 + d) & 0xffffffff;
    H4 = (H4 + e) & 0xffffffff;
  }
  return H0.toHexStr() + H1.toHexStr() + H2.toHexStr() + H3.toHexStr() + H4.toHexStr();
}

// function 'f' [¤4.1.1]

function f(s, x, y, z) {
  switch (s) {
    case 0: return (x & y) ^ (~x & z);           // Ch()
    case 1: return x ^ y ^ z;                    // Parity()
    case 2: return (x & y) ^ (x & z) ^ (y & z);  // Maj()
    case 3: return x ^ y ^ z;                    // Parity()
  }
  return 0;
}

// rotate left (circular left shift) value x
// by n positions [¤3.2.5]

function ROTL(x, n) {
    return (x<<n) | (x>>>(32-n));
}

// extend Number class with a tailored hex-string method
//   (note toString(16) is implementation-dependant, and
//   in IE returns signed numbers when used on full words)

Number.prototype.toHexStr = function() {
  var s = "", v;
  for (var i = 7; i >= 0; i--) {
    v = (this >>> (i * 4)) & 0xf;
    s += v.toString(16);
  }
  return s;
};