text: // -*- 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_;
  }
  }
  