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/*=============================================================================
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
'bytesPerSample' 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, const char ** argv) {
struct pam inpam, outpam;
tuple * intuplerow;
tuple * outtuplerow;
unsigned int row;
pm_proginit(&argc, argv);
pnm_readpaminit(stdin, &inpam, PAM_STRUCT_SIZE(tuple_type));
outpam = inpam;
outpam.file = stdout;
pnm_writepaminit(&outpam);
/* We read the samples as if the maxval is 65535 so pnm_readpamrow, which
assumes big-endian samples, doesn't choke on a little-endian sample,
finding it to exceed the maxval. (The pure way to do this would be not
to use libnetpbm row reading and writing facilities on little-endian
pseudo-Netpbm images, but this program isn't important enough to
justify that effort).
*/
inpam.maxval = 65535;
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);
return 0;
}
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