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/*
* Copyright (c) 2009 M Joonas Pihlaja
*
* Permission is hereby granted, free of charge, to any person
* obtaining a copy of this software and associated documentation
* files (the "Software"), to deal in the Software without
* restriction, including without limitation the rights to use,
* copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the
* Software is furnished to do so, subject to the following
* conditions:
*
* The above copyright notice and this permission notice shall be
* included in all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
* OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
* HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
* WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
* OTHER DEALINGS IN THE SOFTWARE.
*/
/* An unpremultiplier using a 64KB division table. It specialises
* constant runs and solid runs of pixels. It has the advantage over
* the others that it can clamp the result into range without any
* additional cost so that the output doesn't overflow should there be
* superluminant pixels in the input. */
#include <stddef.h>
#include <stdint.h>
/* Pixel format config for a 32 bit pixel with 8 bit components. Only
* the location of alpha matters. */
#ifndef ASHIFT
# define ASHIFT 24
#endif
#define RSHIFT ((24 + ASHIFT) % 32)
#define GSHIFT ((16 + ASHIFT) % 32)
#define BSHIFT (( 8 + ASHIFT) % 32)
#define AMASK (255U << ASHIFT)
#define RMASK (255U << RSHIFT)
#define GMASK (255U << GSHIFT)
#define BMASK (255U << BSHIFT)
/* The function to tabulate in the lookup table. Could be anything
* really. */
#define div_func(a,b) (255*(a) / (b))
#define clamp(x) ((x) > 255 ? 255 : (x))
/* The entries division_table[a][b] are defined by
*
* 0 when b = 0
* min(255, ceil(255*a / b)) when b > 0
*
*/
static uint8_t const division_table[256][256] = {
#define R(a,b) ((b) > 0 ? clamp(div_func((a),(b))) : 0)
#define R1(a,i) R(a, i), R(a+1, i), R(a+2, i), R(a+3, i)
#define R2(a,i) R1(a, i), R1(a+4, i), R1(a+8, i), R1(a+12, i)
#define R3(a,i) R2(a, i), R2(a+16, i), R2(a+32, i), R2(a+48, i)
#define S(b) { R3(0, b), R3(64, b), R3(128, b), R3(192, b) }
#define S1(b) S(b), S(b+1), S(b+2), S(b+3)
#define S2(b) S1(b), S1(b+4), S1(b+8), S1(b+12)
#define S3(b) S2(b), S2(b+16), S2(b+32), S2(b+48)
S3(0), S3(64), S3(128), S3(192)
};
void
unpremultiply_with_lutb(
uint32_t * restrict dst,
uint32_t const * restrict src,
size_t num_pixels)
{
size_t i = 0;
while (i < num_pixels) {
uint32_t const_in, const_out;
uint32_t accu = -2*255;
uint32_t diff;
{
uint32_t rgba, r, g, b, a;
rgba = const_in = src[i];
a = (rgba >> ASHIFT) & 0xFF;
accu = a;
r = (rgba >> RSHIFT) & 0xFF;
g = (rgba >> GSHIFT) & 0xFF;
b = (rgba >> BSHIFT) & 0xFF;
r = division_table[a][r];
g = division_table[a][g];
b = division_table[a][b];
dst[i] = const_out =
(r<<RSHIFT) | (g<<GSHIFT) | (b<<BSHIFT) | (a<<ASHIFT);
}
if (i+1 >= num_pixels)
return;
{
uint32_t rgba, r, g, b, a;
rgba = src[i+1];
a = (rgba >> ASHIFT) & 0xFF;
accu += a;
r = (rgba >> RSHIFT) & 0xFF;
g = (rgba >> GSHIFT) & 0xFF;
b = (rgba >> BSHIFT) & 0xFF;
diff = const_in ^ rgba;
r = division_table[a][r];
g = division_table[a][g];
b = division_table[a][b];
dst[i+1] =
(r<<RSHIFT) | (g<<GSHIFT) | (b<<BSHIFT) | (a<<ASHIFT);
}
accu -= 2*255;
i += 2;
if (0 != (diff & accu))
continue;
if (0 == accu) {
uint32_t in;
while (AMASK == ((in = src[i]) & AMASK)) {
dst[i++] = in;
if (i == num_pixels)
return;
}
}
else if (0 == diff) {
while (src[i] == const_in) {
dst[i++] = const_out;
if (i == num_pixels)
return;
}
}
}
}
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