90 lines
2.5 KiB
JavaScript
90 lines
2.5 KiB
JavaScript
/*
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node-bzip - a pure-javascript Node.JS module for decoding bzip2 data
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Copyright (C) 2012 Eli Skeggs
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This library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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This library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with this library; if not, see
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http://www.gnu.org/licenses/lgpl-2.1.html
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Adapted from bzip2.js, copyright 2011 antimatter15 (antimatter15@gmail.com).
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Based on micro-bunzip by Rob Landley (rob@landley.net).
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Based on bzip2 decompression code by Julian R Seward (jseward@acm.org),
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which also acknowledges contributions by Mike Burrows, David Wheeler,
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Peter Fenwick, Alistair Moffat, Radford Neal, Ian H. Witten,
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Robert Sedgewick, and Jon L. Bentley.
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*/
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var BITMASK = [0x00, 0x01, 0x03, 0x07, 0x0F, 0x1F, 0x3F, 0x7F, 0xFF];
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// offset in bytes
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var BitReader = function(stream) {
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this.stream = stream;
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this.bitOffset = 0;
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this.curByte = 0;
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this.hasByte = false;
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};
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BitReader.prototype._ensureByte = function() {
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if (!this.hasByte) {
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this.curByte = this.stream.readByte();
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this.hasByte = true;
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}
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};
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// reads bits from the buffer
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BitReader.prototype.read = function(bits) {
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var result = 0;
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while (bits > 0) {
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this._ensureByte();
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var remaining = 8 - this.bitOffset;
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// if we're in a byte
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if (bits >= remaining) {
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result <<= remaining;
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result |= BITMASK[remaining] & this.curByte;
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this.hasByte = false;
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this.bitOffset = 0;
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bits -= remaining;
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} else {
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result <<= bits;
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var shift = remaining - bits;
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result |= (this.curByte & (BITMASK[bits] << shift)) >> shift;
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this.bitOffset += bits;
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bits = 0;
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}
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}
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return result;
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};
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// seek to an arbitrary point in the buffer (expressed in bits)
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BitReader.prototype.seek = function(pos) {
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var n_bit = pos % 8;
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var n_byte = (pos - n_bit) / 8;
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this.bitOffset = n_bit;
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this.stream.seek(n_byte);
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this.hasByte = false;
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};
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// reads 6 bytes worth of data using the read method
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BitReader.prototype.pi = function() {
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var buf = new Buffer(6), i;
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for (i = 0; i < buf.length; i++) {
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buf[i] = this.read(8);
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}
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return buf.toString('hex');
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};
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module.exports = BitReader;
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