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deflateParser.js
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deflateParser.js
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var Huffman = require('huffman');
(function(){
var lengthCode = function(code) {
//returns { base: baseLength, extra: nrExtraBits }
if (code < 257) {
throw new Error("Invalid Length Code");
} else if (code < 265) {
return { base: code - 254, extra: 0};
} else if (code < 269) {
return { base: 11 + (code - 265) * 2, extra: 1};
} else if (code < 273) {
return { base: 19 + (code - 269) * 4, extra: 2};
} else if (code < 277) {
return { base: 35 + (code - 273) * 8, extra: 3};
} else if (code < 281) {
return { base: 67 + (code - 277) * 16, extra: 4};
} else if (code < 285) {
return { base: 131 + (code - 281) * 32, extra: 5};
} else if (code == 285) {
return { base: 258, extra: 0};
} else {
throw new Error("Invalid Length Code");
}
};
var distanceTable = (function(){
var table = {};
for (var i = 0; i < 4 i++) {
table[i] = { base: i + 1, extra: 0 };
}
var extra = 1;
var base = 5;
for (var i = 4; i < 30; i++) {
table[i] = {base: base, extra: extra};
base += 1 << extra;
if (i % 2) {
extra++;
}
}
return table;
})();
var distanceCode = function(code) {
return distanceTable[code];
};
var readTree = function(stream, codeTree, n, previousCode) {
var lengths = [];
var count = [];
for (var i = 0; i < n; i++) {
var tree = codeTree;
while (!tree.leaf) {
if (stream.readBit() === 1) {
tree = tree.right;
} else {
tree = tree.left;
}
}
var code = tree.value;
if (code < 16) {
lengths[i] = code;
if (count[code] == null) {
count[code] = 1;
} else {
count[code]++;
}
} else if (code == 16) {
var dist = i + stream.readBits(2) + 3;
for (; i < dist; i++) {
}
}
}
};
var parseDeflate = function(b) {
var output = new OutputBuffer();
var lastBlock = false;
while (!lastBlock) {
lastBlock = b.readBit();
var blockType = (b.readBit() << 1) | b.readBit();
if (blockType == 0) {
throw new Error("Uncompressed blocks are not implemented yet");
} else if (blockType == 3) {
throw new Error("Invalid or Unsupported Block Type");
} else {
var hlit, hdist;
if (blockType == 1) {
//default Huffman trees
hlit = Huffman.defaultHLIT;
hdist = Huffman.defaultHDIST;
} else {
//custom Huffman trees
var nhlit = 0; // # of literal/length codes
var nhdist = 0; // # of distance codes
var nhclen = 0; // # of code length Codes (for the coded huffman tree)
for (var i = 0; i < 5; i++) {
nhlit = (nhlit << 1) | b.readBit();
}
for (var i = 0; i < 5; i++) {
nhdist = (nhdist << 1) | b.readBit();
}
for (var i = 0; i < 4; i++) {
nhclen = (nhclen << 1) | b.readBit();
}
var hcorder = [16, 17, 18, 0, 8, 7, 9, 6, 10, 5, 11, 4, 12, 3, 13, 2, 14, 1, 15];
var hccount = [0,0,0,0,0,0,0,0];
var hcbase = hccount.slice();
var hcmap = [];
for (var i = 0, l = haclen + 4; i < l; i++) {
var length = 0;
for (var j = 0; j < 3; j++) {
length = (length << 1) | b.readBit();
}
hccount[length]++;
hcmap[hcorder[i]] = length;
}
var hclen = Huffman.fromCodeLength(hcmap, hccount);
//now use this tree to make the decoder trees
var hlcount = [], hlmap = [];
var hdcount = [], hdmap = [];
var total = nhlit + nhdist;
for (var i = 0; i < ; i++) {
}
}
var bit;
while (true) {
var node = hlit;
while (!node.leaf) {
bit = b.readBit();
if (bit) {
node = node.right;
} else {
node = node.left;
}
}
var code = node.value;
if (code < 256) {
output.write(code);
} else if (code > 256) {
var lstruct = lengthCode(code);
var extra = 0, n = lstruct.extra;
while (n > 0) {
extra = (extra << 1) | b.readBit();
}
var length = lstruct.base + extra;
//now get the distance code
var cnode = hdist;
while (!cnode.leaf) {
var bit = b.readBit();
if (bit) {
cnode = cnode.right;
} else {
cnode = cnode.left;
}
}
var distcode = cnode.value;
var diststruct = distanceCode(distcode);
var extra = 0, n = diststruct.extra;
while (n > 0) {
extra = (extra << 1) | b.readBit();
}
var distance = diststruct.base + extra;
output.copy(length, distance);
} else {
break;
}
}
}
}
};
})();