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/*
* The Python Imaging Library.
* $Id: BitDecode.c 2278 2005-02-07 20:27:33Z fredrik $
*
* decoder for packed bitfields (converts to floating point)
*
* history:
* 97-05-31 fl created (much more than originally intended)
*
* Copyright (c) Fredrik Lundh 1997.
* Copyright (c) Secret Labs AB 1997.
*
* See the README file for information on usage and redistribution.
*/
#include "Imaging.h"
#include "Bit.h"
int
ImagingBitDecode(Imaging im, ImagingCodecState state, UINT8* buf, int bytes)
{
BITSTATE* bitstate = state->context;
UINT8* ptr;
if (state->state == 0) {
/* Initialize context variables */
/* this decoder only works for float32 image buffers */
if (im->type != IMAGING_TYPE_FLOAT32) {
state->errcode = IMAGING_CODEC_CONFIG;
return -1;
}
/* sanity check */
if (bitstate->bits < 1 || bitstate->bits >= 32) {
state->errcode = IMAGING_CODEC_CONFIG;
return -1;
}
bitstate->mask = (1<<bitstate->bits)-1;
if (bitstate->sign)
bitstate->signmask = (1<<(bitstate->bits-1));
/* check image orientation */
if (state->ystep < 0) {
state->y = state->ysize-1;
state->ystep = -1;
} else
state->ystep = 1;
state->state = 1;
}
ptr = buf;
while (bytes > 0) {
UINT8 byte = *ptr;
ptr++;
bytes--;
/* get a byte from the input stream and insert in the bit buffer */
if (bitstate->fill&1)
/* fill MSB first */
bitstate->bitbuffer |= (unsigned long) byte << bitstate->bitcount;
else
/* fill LSB first */
bitstate->bitbuffer = (bitstate->bitbuffer << 8) | byte;
bitstate->bitcount += 8;
while (bitstate->bitcount >= bitstate->bits) {
/* get a pixel from the bit buffer */
unsigned long data;
FLOAT32 pixel;
if (bitstate->fill&2) {
/* store LSB first */
data = bitstate->bitbuffer & bitstate->mask;
if (bitstate->bitcount > 32)
/* bitbuffer overflow; restore it from last input byte */
bitstate->bitbuffer = byte >> (8 - (bitstate->bitcount -
bitstate->bits));
else
bitstate->bitbuffer >>= bitstate->bits;
} else
/* store MSB first */
data = (bitstate->bitbuffer >> (bitstate->bitcount -
bitstate->bits))
& bitstate->mask;
bitstate->bitcount -= bitstate->bits;
if (bitstate->lutsize > 0) {
/* map through lookup table */
if (data <= 0)
pixel = bitstate->lut[0];
else if (data >= bitstate->lutsize)
pixel = bitstate->lut[bitstate->lutsize-1];
else
pixel = bitstate->lut[data];
} else {
/* convert */
if (data & bitstate->signmask)
/* image memory contains signed data */
pixel = (FLOAT32) (INT32) (data | ~bitstate->mask);
else
pixel = (FLOAT32) data;
}
*(FLOAT32*)(&im->image32[state->y][state->x]) = pixel;
/* step forward */
if (++state->x >= state->xsize) {
/* new line */
state->y += state->ystep;
if (state->y < 0 || state->y >= state->ysize) {
/* end of file (errcode = 0) */
return -1;
}
state->x = 0;
/* reset bit buffer */
if (bitstate->pad > 0)
bitstate->bitcount = 0;
}
}
}
return ptr - buf;
}
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