ghaction-upx/node_modules/seek-bzip/lib/bitreader.js

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2020-01-17 01:36:42 -07:00
/*
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;