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