function sha1Hash(msg) 
{
    // constants [§4.2.1]
    var K = [0x5a827999, 0x6ed9eba1, 0x8f1bbcdc, 0xca62c1d6];


    // PREPROCESSING 

    msg += String.fromCharCode(0x80); // add trailing '1' bit to string [§5.1.1]

    // convert string msg into 512-bit/16-integer blocks arrays of ints [§5.2.1]
    var l = Math.ceil(msg.length / 4) + 2;  // long enough to contain msg plus 2-word length
    var N = Math.ceil(l / 16);              // in N 16-int blocks
    var M = new Array(N);
    for (var i = 0; i < N; i++) {
        M[i] = new Array(16);
        for (var j = 0; j < 16; j++) {  // encode 4 chars per integer, big-endian encoding
            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 (var i = 0; i < N; i++) {

        // 1 - prepare message schedule 'W'
        for (var t = 0; t < 16; t++) W[t] = M[i][t];
        for (var 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 (var t = 0; t < 80; t++) {
            var s = Math.floor(t / 20); // seq for blocks of 'f' functions and 'K' constants
            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
        H0 = (H0 + a) & 0xffffffff;  // note 'addition modulo 2^32'
        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()
    }
}

//
// 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;
}