
function library(_){

    function sha256(msg, utf8encode) {
        var Sha256 = {};  // Sha256 namespace

        Sha256.ROTR = function(n, x) { return (x >>> n) | (x << (32-n)); }
        Sha256.Sigma0 = function(x) { return Sha256.ROTR(2,  x) ^ Sha256.ROTR(13, x) ^ Sha256.ROTR(22, x); }
        Sha256.Sigma1 = function(x) { return Sha256.ROTR(6,  x) ^ Sha256.ROTR(11, x) ^ Sha256.ROTR(25, x); }
        Sha256.sigma0 = function(x) { return Sha256.ROTR(7,  x) ^ Sha256.ROTR(18, x) ^ (x>>>3);  }
        Sha256.sigma1 = function(x) { return Sha256.ROTR(17, x) ^ Sha256.ROTR(19, x) ^ (x>>>10); }
        Sha256.Ch = function(x, y, z)  { return (x & y) ^ (~x & z); }
        Sha256.Maj = function(x, y, z) { return (x & y) ^ (x & z) ^ (y & z); }
        
        //
        // hexadecimal representation of a number 
        //   (note toString(16) is implementation-dependant, and  
        //   in IE returns signed numbers when used on full words)
        //
        Sha256.toHexStr = function(n) {
          var s="", v;
          for (var i=7; i>=0; i--) { v = (n>>>(i*4)) & 0xf; s += v.toString(16); }
          return s;
        }
        
        
        /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -  */
        /*  Utf8 class: encode / decode between multi-byte Unicode characters and UTF-8 multiple          */
        /*              single-byte character encoding (c) Chris Veness 2002-2010                         */
        /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -  */
        
        var Utf8 = {};  // Utf8 namespace
        
        /**
         * Encode multi-byte Unicode string into utf-8 multiple single-byte characters 
         * (BMP / basic multilingual plane only)
         *
         * Chars in range U+0080 - U+07FF are encoded in 2 chars, U+0800 - U+FFFF in 3 chars
         *
         * @param {String} strUni Unicode string to be encoded as UTF-8
         * @returns {String} encoded string
         */
        Utf8.encode = function(strUni) {
          // use regular expressions & String.replace callback function for better efficiency 
          // than procedural approaches
          var strUtf = strUni.replace(
              /[\u0080-\u07ff]/g,  // U+0080 - U+07FF => 2 bytes 110yyyyy, 10zzzzzz
              function(c) { 
                var cc = c.charCodeAt(0);
                return String.fromCharCode(0xc0 | cc>>6, 0x80 | cc&0x3f); }
            );
          strUtf = strUtf.replace(
              /[\u0800-\uffff]/g,  // U+0800 - U+FFFF => 3 bytes 1110xxxx, 10yyyyyy, 10zzzzzz
              function(c) { 
                var cc = c.charCodeAt(0); 
                return String.fromCharCode(0xe0 | cc>>12, 0x80 | cc>>6&0x3F, 0x80 | cc&0x3f); }
            );
          return strUtf;
        }
        
        /**
         * Decode utf-8 encoded string back into multi-byte Unicode characters
         *
         * @param {String} strUtf UTF-8 string to be decoded back to Unicode
         * @returns {String} decoded string
         */
        Utf8.decode = function(strUtf) {
          // note: decode 3-byte chars first as decoded 2-byte strings could appear to be 3-byte char!
          var strUni = strUtf.replace(
              /[\u00e0-\u00ef][\u0080-\u00bf][\u0080-\u00bf]/g,  // 3-byte chars
              function(c) {  // (note parentheses for precence)
                var cc = ((c.charCodeAt(0)&0x0f)<<12) | ((c.charCodeAt(1)&0x3f)<<6) | ( c.charCodeAt(2)&0x3f); 
                return String.fromCharCode(cc); }
            );
          strUni = strUni.replace(
              /[\u00c0-\u00df][\u0080-\u00bf]/g,                 // 2-byte chars
              function(c) {  // (note parentheses for precence)
                var cc = (c.charCodeAt(0)&0x1f)<<6 | c.charCodeAt(1)&0x3f;
                return String.fromCharCode(cc); }
            );
          return strUni;
        }
        
        /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -  */

        utf8encode =  (typeof utf8encode == 'undefined') ? true : utf8encode;
        
        // convert string to UTF-8, as SHA only deals with byte-streams
        if (utf8encode) msg = Utf8.encode(msg);
        
        // constants [§4.2.2]
        var 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];
        // initial hash value [§5.3.1]
        var H = [0x6a09e667, 0xbb67ae85, 0x3c6ef372, 0xa54ff53a, 0x510e527f, 0x9b05688c, 0x1f83d9ab, 0x5be0cd19];

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

        // convert string msg into 512-bit/16-integer blocks arrays of ints [§5.2.1]
        var l = msg.length/4 + 2;  // length (in 32-bit integers) of msg + 1 + appended length
        var N = Math.ceil(l/16);   // number of 16-integer-blocks required to hold 'l' ints
        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));
            } // note running off the end of msg is ok 'cos bitwise ops on NaN return 0
        }
        // 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;


        // HASH COMPUTATION [§6.1.2]

        var W = new Array(64); var a, b, c, d, e, f, g, h;
        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<64; t++) W[t] = (Sha256.sigma1(W[t-2]) + W[t-7] + Sha256.sigma0(W[t-15]) + W[t-16]) & 0xffffffff;

            // 2 - initialise working variables a, b, c, d, e, f, g, h with previous hash value
            a = H[0]; b = H[1]; c = H[2]; d = H[3]; e = H[4]; f = H[5]; g = H[6]; h = H[7];

            // 3 - main loop (note 'addition modulo 2^32')
            for (var t=0; t<64; t++) {
                var T1 = h + Sha256.Sigma1(e) + Sha256.Ch(e, f, g) + K[t] + W[t];
                var T2 = Sha256.Sigma0(a) + Sha256.Maj(a, b, c);
                h = g;
                g = f;
                f = e;
                e = (d + T1) & 0xffffffff;
                d = c;
                c = b;
                b = a;
                a = (T1 + T2) & 0xffffffff;
            }
             // 4 - compute the new intermediate hash value (note 'addition modulo 2^32')
            H[0] = (H[0]+a) & 0xffffffff;
            H[1] = (H[1]+b) & 0xffffffff; 
            H[2] = (H[2]+c) & 0xffffffff; 
            H[3] = (H[3]+d) & 0xffffffff; 
            H[4] = (H[4]+e) & 0xffffffff;
            H[5] = (H[5]+f) & 0xffffffff;
            H[6] = (H[6]+g) & 0xffffffff; 
            H[7] = (H[7]+h) & 0xffffffff; 
        }

        return Sha256.toHexStr(H[0]) + Sha256.toHexStr(H[1]) + Sha256.toHexStr(H[2]) + Sha256.toHexStr(H[3]) + 
               Sha256.toHexStr(H[4]) + Sha256.toHexStr(H[5]) + Sha256.toHexStr(H[6]) + Sha256.toHexStr(H[7]);
    };

    sha256.library = library;

    return(sha256);
}

exports.library = library;
