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inflate.js
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inflate.js
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/* -*- Mode: js; js-indent-level: 2; indent-tabs-mode: nil; tab-width: 2 -*- */
/* vim: set shiftwidth=2 tabstop=2 autoindent cindent expandtab: */
/*
* Copyright 2013 Mozilla Foundation
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
/*global slice, splice, max, fail, Stream */
var codeLengthOrder = [16, 17, 18, 0, 8, 7, 9, 6, 10, 5, 11, 4, 12, 3, 13, 2, 14, 1, 15];
var distanceCodes = [];
var distanceExtraBits = [];
for (var i = 0, j = 0, code = 1; i < 30; ++i) {
distanceCodes[i] = code;
code += 1 << (distanceExtraBits[i] = ~~((j += (i > 2 ? 1 : 0)) / 2));
}
var bitLengths = [];
for (var i = 0; i < 32; ++i)
bitLengths[i] = 5;
var fixedDistanceTable = makeHuffmanTable(bitLengths);
var lengthCodes = [];
var lengthExtraBits = [];
for (var i = 0, j = 0, code = 3; i < 29; ++i) {
lengthCodes[i] = code - (i == 28 ? 1 : 0);
code += 1 << (lengthExtraBits[i] = ~~(((j += (i > 4 ? 1 : 0)) / 4) % 6));
}
for (var i = 0; i < 288; ++i)
bitLengths[i] = i < 144 || i > 279 ? 8 : (i < 256 ? 9 : 7);
var fixedLiteralTable = makeHuffmanTable(bitLengths);
function makeHuffmanTable(bitLengths) {
var maxBits = max.apply(null, bitLengths);
var numLengths = bitLengths.length;
var size = 1 << maxBits;
var codes = new Uint32Array(size);
for (var code = 0, len = 1, skip = 2; len <= maxBits; code <<= 1, ++len, skip <<= 1) {
for (var val = 0; val < numLengths; ++val) {
if (bitLengths[val] === len) {
var lsb = 0;
for (var i = 0; i < len; ++i)
lsb = (lsb * 2) + ((code >> i) & 1);
for (var i = lsb; i < size; i += skip)
codes[i] = (len << 16) | val;
++code;
}
}
}
return { codes: codes, maxBits: maxBits };
}
function verifyDeflateHeader(bytes) {
var header = (bytes[0] << 8) | bytes[1];
assert((header & 0x0f00) === 0x0800, 'unknown compression method', 'inflate');
assert((header % 31) === 0, 'bad FCHECK', 'inflate');
assert(!(header & 0x20), 'FDICT bit set', 'inflate');
}
function createInflatedStream(bytes, outputLength) {
verifyDeflateHeader(bytes);
var stream = new Stream(bytes, 2);
var output = {
data: new Uint8Array(outputLength),
available: 0,
completed: false
};
var state = {};
do {
inflateBlock(stream, output, state);
} while (!output.completed && stream.pos < stream.end);
return new Stream(output.data, 0, output.available);
}
var InflateNoDataError = {};
function inflateBlock(stream, output, state) {
var header = state.header || (state.header = readBits(stream.bytes, stream, 3));
switch (header >> 1) {
case 0:
stream.align();
var pos = stream.pos;
if (stream.end - pos < 4) {
throw InflateNoDataError;
}
var len = stream.getUint16(pos, true);
var nlen = stream.getUint16(pos + 2, true);
assert((~nlen & 0xffff) === len, 'bad uncompressed block length', 'inflate');
if (stream.end - pos < 4 + len) {
throw InflateNoDataError;
}
var begin = pos + 4;
var end = stream.pos = begin + len;
var sbytes = stream.bytes, dbytes = output.data;
splice.apply(dbytes, [output.available, len].concat(slice.call(sbytes, begin, end)));
output.available += len;
break;
case 1:
inflate(stream, output, fixedLiteralTable, fixedDistanceTable, state);
break;
case 2:
var distanceTable, literalTable;
if (state.distanceTable) {
distanceTable = state.distanceTable;
literalTable = state.literalTable;
} else {
var sbytes = stream.bytes;
var savedBufferPos = stream.pos;
var savedBitBuffer = stream.bitBuffer;
var savedBitLength = stream.bitLength;
var bitLengths = [];
var numLiteralCodes, numDistanceCodes;
try {
numLiteralCodes = readBits(sbytes, stream, 5) + 257;
numDistanceCodes = readBits(sbytes, stream, 5) + 1;
var numCodes = numLiteralCodes + numDistanceCodes;
var numLengthCodes = readBits(sbytes, stream, 4) + 4;
for (var i = 0; i < 19; ++i)
bitLengths[codeLengthOrder[i]] = i < numLengthCodes ? readBits(sbytes, stream, 3) : 0;
var codeLengthTable = makeHuffmanTable(bitLengths);
bitLengths = [];
var i = 0;
var prev = 0;
while (i < numCodes) {
var j = 1;
var sym = readCode(sbytes, stream, codeLengthTable);
switch(sym){
case 16:
j = readBits(sbytes, stream, 2) + 3;
sym = prev;
break;
case 17:
j = readBits(sbytes, stream, 3) + 3;
sym = 0;
break;
case 18:
j = readBits(sbytes, stream, 7) + 11;
sym = 0;
break;
default:
prev = sym;
}
while (j--)
bitLengths[i++] = sym;
}
} catch (e) {
stream.pos = savedBufferPos;
stream.bitBuffer = savedBitBuffer;
stream.bitLength = savedBitLength;
throw e;
}
distanceTable = state.distanceTable = makeHuffmanTable(bitLengths.splice(numLiteralCodes, numDistanceCodes));
literalTable = state.literalTable = makeHuffmanTable(bitLengths);
}
inflate(stream, output, literalTable, distanceTable, state);
state.distanceTable = null;
state.literalTable = null;
break;
default:
fail('unknown block type', 'inflate');
}
state.header = null;
output.completed = !!(header & 1);
}
function readBits(bytes, stream, size) {
var bitBuffer = stream.bitBuffer;
var bitLength = stream.bitLength;
if (size > bitLength) {
var pos = stream.pos;
var end = stream.end;
do {
if (pos >= end) {
stream.pos = pos;
stream.bitBuffer = bitBuffer;
stream.bitLength = bitLength;
throw InflateNoDataError;
}
bitBuffer |= bytes[pos++] << bitLength;
bitLength += 8;
} while (size > bitLength);
stream.pos = pos;
}
stream.bitBuffer = bitBuffer >>> size;
stream.bitLength = bitLength - size;
return bitBuffer & ((1 << size) - 1);
}
function inflate(stream, output, literalTable, distanceTable, state) {
var pos = output.available;
var dbytes = output.data;
var sbytes = stream.bytes;
var sym = state.sym || readCode(sbytes, stream, literalTable);
while (sym !== 256) {
if (sym < 256) {
dbytes[pos++] = sym;
} else {
state.sym = sym;
sym -= 257;
var len = state.len || (state.len = lengthCodes[sym] + readBits(sbytes, stream, lengthExtraBits[sym]));
var sym2 = state.sym2 || (state.sym2 = readCode(sbytes, stream, distanceTable));
var distance = distanceCodes[sym2] + readBits(sbytes, stream, distanceExtraBits[sym2]);
var i = pos - distance;
while (len--)
dbytes[pos++] = dbytes[i++];
state.sym2 = null;
state.len = null;
state.sym = null;
}
output.available = pos;
sym = readCode(sbytes, stream, literalTable);
}
}
function readCode(bytes, stream, codeTable) {
var bitBuffer = stream.bitBuffer;
var bitLength = stream.bitLength;
var maxBits = codeTable.maxBits;
if (maxBits > bitLength) {
var pos = stream.pos;
var end = stream.end;
do {
if (pos >= end) {
stream.pos = pos;
stream.bitBuffer = bitBuffer;
stream.bitLength = bitLength;
throw InflateNoDataError;
}
bitBuffer |= bytes[pos++] << bitLength;
bitLength += 8;
} while (maxBits > bitLength);
stream.pos = pos;
}
var code = codeTable.codes[bitBuffer & ((1 << maxBits) - 1)];
var len = code >> 16;
assert(len, 'bad encoding', 'inflate');
stream.bitBuffer = bitBuffer >>> len;
stream.bitLength = bitLength - len;
return code & 0xffff;
}