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build/node_modules/seek-bzip/lib/bitreader.js

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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;