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/*
* Copyright (c) 2009 M Joonas Pihlaja
* Copyright (c) 2009 Paul-Virak Khuong
*
* 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 reciprocal multiplication. It specialises
* constant runs and solid runs of pixels with low overhead loops and
* uses only a 1KB table of reciprocals. */
#include <stdint.h>
#include <stddef.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)
/* Set to 1 if the input can have superluminant pixels. */
#define DO_CLAMP_INPUT 0
/* Shift x left by y bits. Supports negative y for right shifts. */
#define SHIFT(x, y) ((y) < 0 ? (x) >> (-(y)) : (x) << (y))
#define ceil_div(a,b) ((a) + (b)-1) / (b)
/* The reciprocal_table[i] entries are defined by
*
* 0 when i = 0
* 255 / i when i > 0
*
* represented in fixed point format with RECIPROCAL_BITS of
* precision and errors rounded up. */
#define RECIPROCAL_BITS 16
static uint32_t const reciprocal_table[256] = {
# define R(i) ((i) ? ceil_div(255*(1<<RECIPROCAL_BITS), (i)) : 0)
# define R1(i) R(i), R(i+1), R(i+2), R(i+3)
# define R2(i) R1(i), R1(i+4), R1(i+8), R1(i+12)
# define R3(i) R2(i), R2(i+16), R2(i+32), R2(i+48)
R3(0), R3(64), R3(128), R3(192)
};
/* Transfer num_pixels unpremultiplied pixels from src[] to dst[].
* This version uses a short probe period of a few pixels to identify
* runs of constant or solid pixels. When a run is identified it
* falls into a special case loop for the duration of the run. */
void
unpremultiply_with_invb(
uint32_t * restrict dst,
uint32_t const * restrict src,
size_t num_pixels)
{
size_t i = 0;
while (i < num_pixels) {
/* We want to identify long runs of constant input pixels and
* cache the unpremultiplied. */
uint32_t const_in, const_out;
/* Diff is the or of all bitwise differences from const_in
* during the probe period. If it is zero after the probe
* period then every input pixel was identical in the
* probe. */
unsigned diff = 0;
/* Accumulator for all alphas of the probe period pixels,
* biased to make the sum zero if the */
unsigned accu = -2*255;
{
uint32_t rgba, a, r, g, b, recip;
rgba = const_in = src[i];
a = (rgba >> ASHIFT) & 255;
accu += a;
r = (rgba >> RSHIFT) & 255;
g = (rgba >> GSHIFT) & 255;
b = (rgba >> BSHIFT) & 255;
recip = reciprocal_table[a];
#if DO_CLAMP_INPUT
r = r < a ? r : a;
g = g < a ? g : a;
b = b < a ? b : a;
#endif
r = SHIFT(r * recip, RSHIFT - RECIPROCAL_BITS);
g = SHIFT(g * recip, GSHIFT - RECIPROCAL_BITS);
b = SHIFT(b * recip, BSHIFT - RECIPROCAL_BITS);
dst[i] = const_out =
(r & RMASK) | (g & GMASK) | (b & BMASK) | (rgba & AMASK);
}
if (i + 1 == num_pixels)
return;
{
uint32_t rgba, a, r, g, b, recip;
rgba = src[i+1];
a = (rgba >> ASHIFT) & 255;
accu += a;
r = (rgba >> RSHIFT) & 255;
g = (rgba >> GSHIFT) & 255;
b = (rgba >> BSHIFT) & 255;
recip = reciprocal_table[a];
#if DO_CLAMP_INPUT
r = r < a ? r : a;
g = g < a ? g : a;
b = b < a ? b : a;
#endif
diff = rgba ^ const_in;
r = SHIFT(r * recip, RSHIFT - RECIPROCAL_BITS);
g = SHIFT(g * recip, GSHIFT - RECIPROCAL_BITS);
b = SHIFT(b * recip, BSHIFT - RECIPROCAL_BITS);
dst[i+1] =
(r & RMASK) | (g & GMASK) | (b & BMASK) | (rgba & AMASK);
}
i += 2;
/* Fall into special cases if we have special
* circumstances. */
if (0 != (accu & diff))
continue;
if (0 == accu) { /* a run of solid pixels. */
uint32_t in;
while (AMASK == ((in = src[i]) & AMASK)) {
dst[i++] = in;
if (i == num_pixels) return;
}
} else if (0 == diff) { /* a run of constant pixels. */
while (src[i] == const_in) {
dst[i++] = const_out;
if (i == num_pixels) return;
}
}
}
}
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