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);
		case 1:
			return x ^ y ^ z;
		case 2:
			return (x & y) ^ (x & z) ^ (y & z);
		case 3:
			return x ^ y ^ z;
	}
}

//
// 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;
}