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#include "fitz.h"
/* TODO: check if this works with 16bpp images */
enum { MAXC = 32 };
typedef struct fz_predict_s fz_predict;
struct fz_predict_s
{
fz_stream *chain;
int predictor;
int columns;
int colors;
int bpc;
int stride;
int bpp;
unsigned char *in;
unsigned char *out;
unsigned char *ref;
unsigned char *rp, *wp;
};
static inline int
getcomponent(unsigned char *buf, int x, int bpc)
{
switch (bpc)
{
case 1: return buf[x / 8] >> (7 - (x % 8)) & 0x01;
case 2: return buf[x / 4] >> ((3 - (x % 4)) * 2) & 0x03;
case 4: return buf[x / 2] >> ((1 - (x % 2)) * 4) & 0x0f;
case 8: return buf[x];
}
return 0;
}
static inline void
putcomponent(unsigned char *buf, int x, int bpc, int value)
{
switch (bpc)
{
case 1: buf[x / 8] |= value << (7 - (x % 8)); break;
case 2: buf[x / 4] |= value << ((3 - (x % 4)) * 2); break;
case 4: buf[x / 2] |= value << ((1 - (x % 2)) * 4); break;
case 8: buf[x] = value; break;
}
}
static inline int
paeth(int a, int b, int c)
{
/* The definitions of ac and bc are correct, not a typo. */
int ac = b - c, bc = a - c, abcc = ac + bc;
int pa = ABS(ac);
int pb = ABS(bc);
int pc = ABS(abcc);
return pa <= pb && pa <= pc ? a : pb <= pc ? b : c;
}
static void
fz_predicttiff(fz_predict *state, unsigned char *out, unsigned char *in, int len)
{
int left[MAXC];
int i, k;
for (k = 0; k < state->colors; k++)
left[k] = 0;
for (i = 0; i < state->columns; i++)
{
for (k = 0; k < state->colors; k++)
{
int a = getcomponent(in, i * state->colors + k, state->bpc);
int b = a + left[k];
int c = b % (1 << state->bpc);
putcomponent(out, i * state->colors + k, state->bpc, c);
left[k] = c;
}
}
}
static void
fz_predictpng(fz_predict *state, unsigned char *out, unsigned char *in, int len, int predictor)
{
int bpp = state->bpp;
int i;
unsigned char *ref = state->ref;
switch (predictor)
{
case 0:
memcpy(out, in, len);
break;
case 1:
for (i = bpp; i > 0; i--)
{
*out++ = *in++;
}
for (i = len - bpp; i > 0; i--)
{
*out = *in++ + out[-bpp];
out++;
}
break;
case 2:
for (i = bpp; i > 0; i--)
{
*out++ = *in++ + *ref++;
}
for (i = len - bpp; i > 0; i--)
{
*out++ = *in++ + *ref++;
}
break;
case 3:
for (i = bpp; i > 0; i--)
{
*out++ = *in++ + (*ref++) / 2;
}
for (i = len - bpp; i > 0; i--)
{
*out = *in++ + (out[-bpp] + *ref++) / 2;
out++;
}
break;
case 4:
for (i = bpp; i > 0; i--)
{
*out++ = *in++ + paeth(0, *ref++, 0);
}
for (i = len - bpp; i > 0; i --)
{
*out = *in++ + paeth(out[-bpp], *ref, ref[-bpp]);
ref++;
out++;
}
break;
}
}
static int
readpredict(fz_stream *stm, unsigned char *buf, int len)
{
fz_predict *state = stm->state;
unsigned char *p = buf;
unsigned char *ep = buf + len;
int ispng = state->predictor >= 10;
int n;
while (state->rp < state->wp && p < ep)
*p++ = *state->rp++;
while (p < ep)
{
n = fz_read(state->chain, state->in, state->stride + ispng);
if (n < 0)
return fz_rethrow(n, "read error in prediction filter");
if (n == 0)
return p - buf;
if (state->predictor == 1)
memcpy(state->out, state->in, n);
else if (state->predictor == 2)
fz_predicttiff(state, state->out, state->in, n);
else
{
fz_predictpng(state, state->out, state->in + 1, n - 1, state->in[0]);
memcpy(state->ref, state->out, state->stride);
}
state->rp = state->out;
state->wp = state->out + n - ispng;
while (state->rp < state->wp && p < ep)
*p++ = *state->rp++;
}
return p - buf;
}
static void
closepredict(fz_stream *stm)
{
fz_predict *state = stm->state;
fz_close(state->chain);
fz_free(state->in);
fz_free(state->out);
fz_free(state->ref);
fz_free(state);
}
fz_stream *
fz_openpredict(fz_stream *chain, fz_obj *params)
{
fz_predict *state;
fz_obj *obj;
state = fz_malloc(sizeof(fz_predict));
state->chain = chain;
state->predictor = 1;
state->columns = 1;
state->colors = 1;
state->bpc = 8;
obj = fz_dictgets(params, "Predictor");
if (obj)
state->predictor = fz_toint(obj);
if (state->predictor != 1 && state->predictor != 2 &&
state->predictor != 10 && state->predictor != 11 &&
state->predictor != 12 && state->predictor != 13 &&
state->predictor != 14 && state->predictor != 15)
{
fz_warn("invalid predictor: %d", state->predictor);
state->predictor = 1;
}
obj = fz_dictgets(params, "Columns");
if (obj)
state->columns = fz_toint(obj);
obj = fz_dictgets(params, "Colors");
if (obj)
state->colors = fz_toint(obj);
obj = fz_dictgets(params, "BitsPerComponent");
if (obj)
state->bpc = fz_toint(obj);
state->stride = (state->bpc * state->colors * state->columns + 7) / 8;
state->bpp = (state->bpc * state->colors + 7) / 8;
state->in = fz_malloc(state->stride + 1);
state->out = fz_malloc(state->stride);
state->ref = fz_malloc(state->stride);
state->rp = state->out;
state->wp = state->out;
memset(state->ref, 0, state->stride);
return fz_newstream(state, readpredict, closepredict);
}
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