OSG::BitPacker Class Reference

00071     : _numBitsToPack(1),
00072       _nextBit      (0)
00073 {
00074     while(true)
00075     {
00076         UInt32 maxValue = (UInt32) (1 << _numBitsToPack) - 1;
00077         if (maxValue >= max)
00078             break;
00079 
00080         ++_numBitsToPack;
00081     }
00082 
00083     // calc buffer size.
00084     UInt32 lenInBytes = (_numBitsToPack * size + 7) / 8;
00085 
00086     _buffer.resize(lenInBytes);
00087     memset(&_buffer[0], 0, lenInBytes * sizeof(UInt8)); // unneccessary ?
00088 }

00091 {
00092     UInt32 numBitsToPack = _numBitsToPack;
00093 
00094     // Scoot the value bits up to the top of the word; this makes
00095     // them easier to work with.
00096     value <<= (BITS_PER_WORD - numBitsToPack);
00097 
00098     // First we do the hard part: pack bits into the first u8,
00099     // which may already have bits in it.
00100 
00101     Int32 byteIndex     = (_nextBit / 8);
00102     Int32 bitIndex      = (_nextBit % 8);
00103     Int32 spaceCurrByte = (8 - bitIndex) & 0x7;
00104 
00105     // Update _nextBit for the next call; we don't need
00106     // the old value any more
00107     _nextBit += numBitsToPack;
00108 
00109     UInt8 *dest = &_buffer[0] + byteIndex;
00110 
00111     if(spaceCurrByte)
00112     {
00113         Int32 toCopy = spaceCurrByte;
00114 
00115         if(toCopy > numBitsToPack)
00116         {
00117             // We don't have enough bits to fill up this u8.
00118             toCopy = numBitsToPack;
00119         }
00120 
00121         UInt32 fillBits = value >> (BITS_PER_WORD - spaceCurrByte);
00122         *dest |= fillBits;
00123 
00124         numBitsToPack -= toCopy;
00125         dest++;
00126         value <<= toCopy;
00127     }
00128 
00129     // Now we do the fast and easy part for what is hopefully
00130     // the bulk of the data.
00131     while(value)
00132     {
00133         *dest++ = value >> (BITS_PER_WORD - 8);
00134         value <<= 8;
00135     }
00136 }

00140 {
00141     return _buffer;
00142 }

00146 {
00147     return _buffer;
00148 }