--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/huffman/bitwriter.cpp Fri May 15 20:13:36 2015 +0300
@@ -0,0 +1,271 @@
+/*
+ * skulltag::BitWriter class - Enables writing arbitrary bit lengths of data.
+ *
+ * Copyright 2009 Timothy Landers
+ * email: code.vortexcortex@gmail.com
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#include "bitwriter.h"
+
+/* The internal buffer of bits is an int which is initiallized to zero.
+ * The Bit Buffer: [00000000000000000000000000000000] - 0 bits stored.
+ *
+ * Bits stored in the bit buffer occupy the most significant bits available.
+ * When bits are stored their order is preserved.
+ * Storing the 5 bits 01011 into the bit buffer would result in:
+ * The Bit Buffer: [01011000000000000000000000000000] - 5 bits stored.
+ *
+ * Additionally storing 0x12f3 (13 bits) would result in:
+ * The Bit Buffer: [01011100101111001100000000000000] - 18 bits stored.
+ *
+ * Data is stored via any of the put(...) functions.
+ *
+ * To retrieve bytes (chars) of data from the bit buffer and empty the bit buffer: flush();
+ * Flushing the bit buffer takes groups of 8 bits (octets) and stores them in the
+ * output buffer at the current byte position. Calling flush() would cause output
+ * to receive 2 bytes (0x5c, 0xbc) == (01011100, 10111100) and the remaining bits would
+ * be moved to the most significant bit positions.
+ * The Bit Buffer: [11000000000000000000000000000000] - 2 bits stored.
+ * Note: The empty bits of the bit buffer must be zero to avoid additional masking operations.
+ * flush() is called automatically if the bit buffer is too full during a call to put(...)
+ *
+ * When the bit storage operation is complete call finish(...). Finish will flush as many full
+ * bytes of data into the output buffer as possible, the remaining bits will be padded out
+ * to a full octet with zeros (on their less significant side), then written to the output
+ * buffer. finish( bytesStored, padding ) passes by reference the number of bytes stored
+ * and number of padding bits added (0 to 7) to the last stored byte.
+ *
+ * Bits are not added one at a time, they are masked, shifted and bitwise OR'ed into
+ * the buffer in as large a group as possible. This allows the BitWriter to add multiple bits in a single
+ * operation instead of calling a function for each 1 bit added.
+ *
+ * Normal usage:
+ *
+ * char * dataArray = new char[ max_output_size ];
+ * BitWriter * buffer = new BitWriter( dataArray, max_output_size );
+ * ...
+ * // various calls to put(...);
+ * ...
+ * int numBytesOutput, paddedBits;
+ * buffer->finish( numBytesOutput, paddedBits );
+ * ...
+ * // do something with dataArray
+ * ...
+ * delete buffer;
+ * delete dataArray;
+ *
+ * */
+
+/** Prevents naming convention problems via encapsulation. */
+namespace skulltag {
+
+ // Static variable initially set to zero as a signal for init()
+ int BitWriter::intSize = 0;
+ int BitWriter::mask[32];
+
+ /** Initializes this BitWriter. */
+ void BitWriter::init(){
+
+ // initialize static variables if not initialized yet.
+ if ( intSize == 0 ){
+ intSize = sizeof maximumBytes;
+ mask[0] = 0;
+
+ // fill mask such that m = { 0, 1, 3, 7, 15, etc. }
+ for ( int i = 1; i < 32; i++ ) mask[i] = (mask[i-1] << 1) | 1;
+ }
+
+ // initialize member variables.
+ bitsAvailable = 0;
+ bytesAvailable = 0;
+ bufferBits = 0;
+ currentByte = 0;
+ maximumBytes = 0;
+ bitsLeft = intSize << 3;
+ }
+
+ /** Creates a new BitWriter. */
+ BitWriter::BitWriter(){
+ init();
+ }
+
+ /** Creates a new BitWriter.
+ * @param output Destination that bits will be written to.
+ * @param max Maximum number of chars to output. */
+ BitWriter::BitWriter( unsigned char * const output, int const &max ){
+ outputBuffer( output, max );
+ }
+
+ /** Sets the output buffer that bytes will be written to.
+ * @param output Destination that bits will be written to.
+ * @param max Maximum number of chars to output.
+ * @return true if successful, false otherwise. */
+ bool BitWriter::outputBuffer( unsigned char * const output, int const &max ){
+ init(); // zero the vars.
+ currentByte = output;
+ if ( output == 0 ) return false;
+ if ( max < 1 ) return false;
+ bytesAvailable = max;
+ bitsAvailable = max << 3;
+ maximumBytes = max;
+ return true;
+ }
+
+ /** Appends a char worth of bits to the buffer.
+ * @param bits the bits to append.
+ * @return true if successful, false otherwise. */
+ bool BitWriter::put( unsigned char const &bits ){
+ return put( (int)bits, 8 );
+ }
+
+ /** Appends a short worth of bits to the buffer.
+ * @param bits the bits to append.
+ * @return true if successful, false otherwise. */
+ bool BitWriter::put( short const &bits ){
+ static int shortBitSize = (sizeof bits) << 3;
+ return put( (int)bits, shortBitSize );
+ }
+ /** Appends an int worth of bits to the buffer.
+ * @param bits the bits to append.
+ * @return true if successful, false otherwise. */
+ bool BitWriter::put( int const &bits ){
+ static int intBitSize = intSize << 3;
+ return put( bits, intBitSize);
+ }
+
+ /** Appends multiple chars from a buffer to this BitWriter.
+ * @param inputBuffer pointer to char data
+ * @param count number of chars to read
+ * @return true if successful, false otherwise. */
+ bool BitWriter::put( unsigned char const * const inputBuffer, int count ){
+ int i = 0;
+
+ // Read in 4 bytes at a time and send all at once to the bit buffer.
+ while ( (i + 3) < count ){
+ if ( !put(
+ ((int)inputBuffer[ i ] << 24) |
+ ((int)inputBuffer[i+1] << 16) |
+ ((int)inputBuffer[i+2] << 8) |
+ (int)inputBuffer[i+3], 32
+ ) ) return false;
+ i+=4;
+ }
+
+ // If any bytes remain, output them one at a time.
+ while ( i < count ){
+ if ( !put( (int)inputBuffer[ i ], 8 ) ) return false;
+ i++;
+ }
+
+ return true;
+ }
+
+ /** Appends a specified number of bits from an int to the buffer.
+ * @param bits the bits to append. <br>
+ * The bits should be stored in the least significant portion of the int.
+ * @param count the number of bits to append.
+ * @return true if successful, false otherwise. */
+ bool BitWriter::put( int const &bits, int count ){
+ if ( count > bitsAvailable ) return false;
+ if ( (bitsLeft < 1) && (!flush()) ) return false;
+ if ( count > bitsLeft ){
+ // not enough space in buffer, fill buffer with top end of input bits then flush.
+ bufferBits |= mask[bitsLeft] & (bits >> (count - bitsLeft));
+ count -= bitsLeft;
+ bitsAvailable -= bitsLeft;
+ bitsLeft = 0;
+
+ // Buffer's full, needs flushing.
+ if (!flush()) return false;
+ }
+
+ // if there are still bits of input...
+ if ( count > 0 ){
+
+ // shift the input bits up to the end of the bit buffer.
+ bufferBits |= (mask[count] & bits) << (bitsLeft - count);
+ bitsAvailable -= count;
+ bitsLeft -= count;
+ }
+ return true;
+ }
+
+ /** Writes any full chars of data stored in this BitWriter to the output char buffer.
+ * @return true if successful, false if an error occurs. */
+ bool BitWriter::flush(){
+ // static var to hold how many bits are in an int.
+ static int intBitSize = intSize << 3;
+ if ( currentByte == 0 ) return false;
+ int numBits = intBitSize - bitsLeft;
+
+ // while there's at least one octet of data in the buffer.
+ while ( numBits > 7 ){
+
+ // fail if no bytes can be written.
+ if ( bytesAvailable <= 0 ) return false;
+
+ // get a byte off the top end of the buffer.
+ *currentByte = (bufferBits >> (intBitSize - 8)) & mask[8];
+
+ // Set variables to reflect the change.
+ currentByte++;
+ bytesAvailable--;
+ bufferBits = bufferBits << 8;
+ bitsLeft += 8;
+ numBits -= 8;
+ }
+ return true;
+ }
+
+ /** Flushes this BitWriter then outputs any partial chars by padding them with zeros. <br>
+ * After calling finish() all other calls to update the BitWriter will fail until a buffer is set via outputBuffer().
+ * @param bytesWritten out: the number of bytes written to the output buffer.
+ * @param paddingBits out: the number of padding bits used in the final byte of output.
+ * @return true if successful, false if an error occurs. */
+ bool BitWriter::finish( int &bytesWritten, int &paddingBits ){
+ static int intBitSize = intSize << 3;
+ // set meaningful return values even if flush() fails.
+ bytesWritten = maximumBytes - bytesAvailable;
+ paddingBits = 0;
+ if ( flush() ){
+ // use a temp var to avoid setting paddingBits to invalid value on failure.
+ int pad = (8 - (intBitSize - bitsLeft)) & 7;
+ if ( pad > 0 ){
+ // all empty bits should be zero. Artificially extend by the number of bits needed.
+ bitsLeft -= pad;
+ if ( !flush() ){
+ // Prevent futher use even on failure.
+ init();
+ return false;
+ }
+ // return the temp bit padding value.
+ paddingBits = pad;
+ }
+ bytesWritten = maximumBytes - bytesAvailable;
+ init(); // set initial state -- no further writing can occur.
+ return true;
+ }
+ // Prevents futher use even on failure.
+ init();
+ return false;
+ }
+
+}