void StringTable::CompressStart(int bpp, int width)
{
m_bpp = bpp;
m_slack = (8 - ((width * bpp) % 8)) % 8;
m_partial |= m_clearCode << m_partialSize;
m_partialSize += m_codeSize;
ClearCompressorTable();
}
void StringTable::Initialize(int minCodeSize)
{
m_done = false;
m_bpp = 8;
m_minCodeSize = minCodeSize;
m_clearCode = 1 << m_minCodeSize;
m_endCode = m_clearCode + 1;
m_partial = 0;
m_partialSize = 0;
m_bufferSize = 0;
ClearCompressorTable();
ClearDecompressorTable();
}
bool StringTable::Compress(BYTE *buf, int *len)
{
if( m_bufferSize == 0 || m_done ) {
return false;
}
int mask = (1 << m_bpp) - 1;
BYTE *bufpos = buf;
while( m_bufferPos < m_bufferSize ) {
//get the current pixel value
char ch = (char)((m_buffer[m_bufferPos] >> m_bufferShift) & mask);
// The next prefix is :
// <the previous LZW code (on 12 bits << 8)> | <the code of the current pixel (on 8 bits)>
int nextprefix = (((m_prefix)<<8)&0xFFF00) + (ch & 0x000FF);
if(firstPixelPassed) {
if( m_strmap[nextprefix] > 0) {
m_prefix = m_strmap[nextprefix];
} else {
m_partial |= m_prefix << m_partialSize;
m_partialSize += m_codeSize;
//grab full bytes for the output buffer
while( m_partialSize >= 8 && bufpos - buf < *len ) {
*bufpos++ = (BYTE)m_partial;
m_partial >>= 8;
m_partialSize -= 8;
}
//add the code to the "table map"
m_strmap[nextprefix] = m_nextCode;
//increment the next highest valid code, increase the code size
if( m_nextCode == (1 << m_codeSize) ) {
m_codeSize++;
}
m_nextCode++;
//if we're out of codes, restart the string table
if( m_nextCode == MAX_LZW_CODE ) {
m_partial |= m_clearCode << m_partialSize;
m_partialSize += m_codeSize;
ClearCompressorTable();
}
// Only keep the 8 lowest bits (prevent problems with "negative chars")
m_prefix = ch & 0x000FF;
}
//increment to the next pixel
if( m_bufferShift > 0 && !(m_bufferPos + 1 == m_bufferSize && m_bufferShift <= m_slack) ) {
m_bufferShift -= m_bpp;
} else {
m_bufferPos++;
m_bufferShift = 8 - m_bpp;
}
//jump out here if the output buffer is full
if( bufpos - buf == *len ) {
return true;
}
} else {
// Specific behavior for the first pixel of the whole image
firstPixelPassed=1;
// Only keep the 8 lowest bits (prevent problems with "negative chars")
m_prefix = ch & 0x000FF;
//increment to the next pixel
if( m_bufferShift > 0 && !(m_bufferPos + 1 == m_bufferSize && m_bufferShift <= m_slack) ) {
m_bufferShift -= m_bpp;
} else {
m_bufferPos++;
m_bufferShift = 8 - m_bpp;
}
//jump out here if the output buffer is full
if( bufpos - buf == *len ) {
return true;
}
}
}
bool StringTable::Compress(BYTE *buf, int *len)
{
if( m_bufferSize == 0 || m_done ) {
return false;
}
int mask = (1 << m_bpp) - 1;
BYTE *bufpos = buf;
while( m_bufferPos < m_bufferSize ) {
//get the current pixel value
char ch = (m_buffer[m_bufferPos] >> m_bufferShift) & mask;
std::string nextprefix = m_prefix + ch;
if( m_strmap.find(nextprefix) != m_strmap.end() ) {
m_prefix = nextprefix;
} else {
m_partial |= m_strmap[m_prefix] << m_partialSize;
m_partialSize += m_codeSize;
//grab full bytes for the output buffer
while( m_partialSize >= 8 && bufpos - buf < *len ) {
*bufpos++ = (BYTE)m_partial;
m_partial >>= 8;
m_partialSize -= 8;
}
//add the string to the table map
m_strmap[nextprefix] = m_nextCode;
//increment the next highest valid code, increase the code size
if( m_nextCode == (1 << m_codeSize) ) {
m_codeSize++;
}
m_nextCode++;
//if we're out of codes, restart the string table
if( m_nextCode == MAX_LZW_CODE ) {
m_partial |= m_clearCode << m_partialSize;
m_partialSize += m_codeSize;
ClearCompressorTable();
}
m_prefix = ch;
}
//increment to the next pixel
if( m_bufferShift > 0 && !(m_bufferPos + 1 == m_bufferSize && m_bufferShift <= m_slack) ) {
m_bufferShift -= m_bpp;
} else {
m_bufferPos++;
m_bufferShift = 8 - m_bpp;
}
//jump out here if the output buffer is full
if( bufpos - buf == *len ) {
return true;
}
}
m_bufferSize = 0;
*len = bufpos - buf;
return true;
}
