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// prototype class for hash functions
function Hash (blockSize, finalSize) {
this._block = new Buffer(blockSize)
this._finalSize = finalSize
this._blockSize = blockSize
this._len = 0
this._s = 0
}
Hash.prototype.update = function (data, enc) {
if (typeof data === 'string') {
enc = enc || 'utf8'
data = new Buffer(data, enc)
}
var l = this._len += data.length
var s = this._s || 0
var f = 0
var buffer = this._block
while (s < l) {
var t = Math.min(data.length, f + this._blockSize - (s % this._blockSize))
var ch = (t - f)
for (var i = 0; i < ch; i++) {
buffer[(s % this._blockSize) + i] = data[i + f]
}
s += ch
f += ch
if ((s % this._blockSize) === 0) {
this._update(buffer)
}
}
this._s = s
return this
}
Hash.prototype.digest = function (enc) {
// Suppose the length of the message M, in bits, is l
var l = this._len * 8
// Append the bit 1 to the end of the message
this._block[this._len % this._blockSize] = 0x80
// and then k zero bits, where k is the smallest non-negative solution to the equation (l + 1 + k) === finalSize mod blockSize
this._block.fill(0, this._len % this._blockSize + 1)
if (l % (this._blockSize * 8) >= this._finalSize * 8) {
this._update(this._block)
this._block.fill(0)
}
// to this append the block which is equal to the number l written in binary
// TODO: handle case where l is > Math.pow(2, 29)
this._block.writeInt32BE(l, this._blockSize - 4)
var hash = this._update(this._block) || this._hash()
return enc ? hash.toString(enc) : hash
}
Hash.prototype._update = function () {
throw new Error('_update must be implemented by subclass')
}
module.exports = Hash
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