BitSource.cpp Example File

 // -*- mode:c++; tab-width:2; indent-tabs-mode:nil; c-basic-offset:2 -*-
 /*
  *  BitSource.cpp
  *  zxing
  *
  *  Created by Christian Brunschen on 09/05/2008.
  *  Copyright 2008 Google UK. All rights reserved.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  *      http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */

 #include <zxing/common/BitSource.h>
 #include <sstream>
 #include <zxing/common/IllegalArgumentException.h>

 namespace zxing {

 int BitSource::readBits(int numBits) {
   if (numBits < 0 || numBits > 32 || numBits > available()) {
     std::ostringstream oss;
     oss << numBits;
     throw IllegalArgumentException(oss.str().c_str());
   }

   int result = 0;

   // First, read remainder from current byte
   if (bitOffset_ > 0) {
     int bitsLeft = 8 - bitOffset_;
     int toRead = numBits < bitsLeft ? numBits : bitsLeft;
     int bitsToNotRead = bitsLeft - toRead;
     int mask = (0xFF >> (8 - toRead)) << bitsToNotRead;
     result = (bytes_[byteOffset_] & mask) >> bitsToNotRead;
     numBits -= toRead;
     bitOffset_ += toRead;
     if (bitOffset_ == 8) {
       bitOffset_ = 0;
       byteOffset_++;
     }
   }

   // Next read whole bytes
   if (numBits > 0) {
     while (numBits >= 8) {
       result = (result << 8) | (bytes_[byteOffset_] & 0xFF);
       byteOffset_++;
       numBits -= 8;
     }

     // Finally read a partial byte
     if (numBits > 0) {
       int bitsToNotRead = 8 - numBits;
       int mask = (0xFF >> bitsToNotRead) << bitsToNotRead;
       result = (result << numBits) | ((bytes_[byteOffset_] & mask) >> bitsToNotRead);
       bitOffset_ += numBits;
     }
   }

   return result;
 }

 int BitSource::available() {
   return 8 * (bytes_->size() - byteOffset_) - bitOffset_;
 }
 }