95 lines
2.9 KiB
JavaScript
95 lines
2.9 KiB
JavaScript
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/*
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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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Permission is hereby granted, free of charge, to any person obtaining
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a copy of this software and associated documentation files (the
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"Software"), to deal in the Software without restriction, including
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without limitation the rights to use, copy, modify, merge, publish,
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distribute, sublicense, and/or sell copies of the Software, and to
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permit persons to whom the Software is furnished to do so, subject to
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the following conditions:
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The above copyright notice and this permission notice shall be
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included in all copies or substantial portions of the Software.
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THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
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EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
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MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
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NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
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LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
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OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
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WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
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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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