/******************************************************************************
pamendian
*******************************************************************************
Reverse the endianness of multi-byte samples in a Netpbm stream.
I.e. convert between the true format and the little endian variation of
it.
******************************************************************************/
#include "pam.h"
static sample
reverseSample(sample const insample, unsigned int const bytesPerSample) {
/*----------------------------------------------------------------------------
Return a sample whose value is the least significant
'bytes_per_sample' bytes, in reverse order.
-----------------------------------------------------------------------------*/
unsigned int bytePos;
sample shiftedInsample;
sample outsample;
shiftedInsample = insample; /* initial value */
outsample = 0; /* initial value */
for (bytePos = 0; bytePos < bytesPerSample; ++bytePos) {
outsample = outsample * 256 + (shiftedInsample & 0xff);
shiftedInsample >>= 8;
}
return outsample;
}
int main(int argc, char *argv[]) {
struct pam inpam, outpam;
tuple * intuplerow;
tuple * outtuplerow;
unsigned int row;
pnm_init(&argc, argv);
pnm_readpaminit(stdin, &inpam, PAM_STRUCT_SIZE(tuple_type));
outpam = inpam;
outpam.file = stdout;
pnm_writepaminit(&outpam);
intuplerow = pnm_allocpamrow(&inpam);
outtuplerow = pnm_allocpamrow(&outpam);
for (row = 0; row < inpam.height; row++) {
unsigned int col;
pnm_readpamrow(&inpam, intuplerow);
for (col = 0; col < inpam.width; col++) {
unsigned int plane;
for (plane = 0; plane < inpam.depth; plane++)
outtuplerow[col][plane] =
reverseSample(intuplerow[col][plane],
inpam.bytes_per_sample);
}
pnm_writepamrow(&outpam, outtuplerow);
}
pnm_freepamrow(outtuplerow);
pnm_freepamrow(intuplerow);
exit(0);
}