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/* filter_sse2_intrinsics.c - SSE2 optimized filter functions
*
* Copyright (c) 2018 Cosmin Truta
* Copyright (c) 2016-2017 Glenn Randers-Pehrson
* Written by Mike Klein and Matt Sarett
* Derived from arm/filter_neon_intrinsics.c
*
* This code is released under the libpng license.
* For conditions of distribution and use, see the disclaimer
* and license in png.h
*/
#include "../pngpriv.h"
#ifdef PNG_READ_SUPPORTED
#if PNG_INTEL_SSE_IMPLEMENTATION > 0
#include <immintrin.h>
/* Functions in this file look at most 3 pixels (a,b,c) to predict the 4th (d).
* They're positioned like this:
* prev: c b
* row: a d
* The Sub filter predicts d=a, Avg d=(a+b)/2, and Paeth predicts d to be
* whichever of a, b, or c is closest to p=a+b-c.
*/
static __m128i load4(const void* p) {
int tmp;
memcpy(&tmp, p, sizeof(tmp));
return _mm_cvtsi32_si128(tmp);
}
static void store4(void* p, __m128i v) {
int tmp = _mm_cvtsi128_si32(v);
memcpy(p, &tmp, sizeof(int));
}
static __m128i load3(const void* p) {
png_uint_32 tmp = 0;
memcpy(&tmp, p, 3);
return _mm_cvtsi32_si128(tmp);
}
static void store3(void* p, __m128i v) {
int tmp = _mm_cvtsi128_si32(v);
memcpy(p, &tmp, 3);
}
void png_read_filter_row_sub3_sse2(png_row_infop row_info, png_bytep row,
png_const_bytep prev)
{
/* The Sub filter predicts each pixel as the previous pixel, a.
* There is no pixel to the left of the first pixel. It's encoded directly.
* That works with our main loop if we just say that left pixel was zero.
*/
size_t rb;
__m128i a, d = _mm_setzero_si128();
png_debug(1, "in png_read_filter_row_sub3_sse2");
rb = row_info->rowbytes;
while (rb >= 4) {
a = d; d = load4(row);
d = _mm_add_epi8(d, a);
store3(row, d);
row += 3;
rb -= 3;
}
if (rb > 0) {
a = d; d = load3(row);
d = _mm_add_epi8(d, a);
store3(row, d);
row += 3;
rb -= 3;
}
PNG_UNUSED(prev)
}
void png_read_filter_row_sub4_sse2(png_row_infop row_info, png_bytep row,
png_const_bytep prev)
{
/* The Sub filter predicts each pixel as the previous pixel, a.
* There is no pixel to the left of the first pixel. It's encoded directly.
* That works with our main loop if we just say that left pixel was zero.
*/
size_t rb;
__m128i a, d = _mm_setzero_si128();
png_debug(1, "in png_read_filter_row_sub4_sse2");
rb = row_info->rowbytes+4;
while (rb > 4) {
a = d; d = load4(row);
d = _mm_add_epi8(d, a);
store4(row, d);
row += 4;
rb -= 4;
}
PNG_UNUSED(prev)
}
void png_read_filter_row_avg3_sse2(png_row_infop row_info, png_bytep row,
png_const_bytep prev)
{
/* The Avg filter predicts each pixel as the (truncated) average of a and b.
* There's no pixel to the left of the first pixel. Luckily, it's
* predicted to be half of the pixel above it. So again, this works
* perfectly with our loop if we make sure a starts at zero.
*/
size_t rb;
const __m128i zero = _mm_setzero_si128();
__m128i b;
__m128i a, d = zero;
png_debug(1, "in png_read_filter_row_avg3_sse2");
rb = row_info->rowbytes;
while (rb >= 4) {
__m128i avg;
b = load4(prev);
a = d; d = load4(row );
/* PNG requires a truncating average, so we can't just use _mm_avg_epu8 */
avg = _mm_avg_epu8(a,b);
/* ...but we can fix it up by subtracting off 1 if it rounded up. */
avg = _mm_sub_epi8(avg, _mm_and_si128(_mm_xor_si128(a,b),
_mm_set1_epi8(1)));
d = _mm_add_epi8(d, avg);
store3(row, d);
prev += 3;
row += 3;
rb -= 3;
}
if (rb > 0) {
__m128i avg;
b = load3(prev);
a = d; d = load3(row );
/* PNG requires a truncating average, so we can't just use _mm_avg_epu8 */
avg = _mm_avg_epu8(a,b);
/* ...but we can fix it up by subtracting off 1 if it rounded up. */
avg = _mm_sub_epi8(avg, _mm_and_si128(_mm_xor_si128(a,b),
_mm_set1_epi8(1)));
d = _mm_add_epi8(d, avg);
store3(row, d);
prev += 3;
row += 3;
rb -= 3;
}
}
void png_read_filter_row_avg4_sse2(png_row_infop row_info, png_bytep row,
png_const_bytep prev)
{
/* The Avg filter predicts each pixel as the (truncated) average of a and b.
* There's no pixel to the left of the first pixel. Luckily, it's
* predicted to be half of the pixel above it. So again, this works
* perfectly with our loop if we make sure a starts at zero.
*/
size_t rb;
const __m128i zero = _mm_setzero_si128();
__m128i b;
__m128i a, d = zero;
png_debug(1, "in png_read_filter_row_avg4_sse2");
rb = row_info->rowbytes+4;
while (rb > 4) {
__m128i avg;
b = load4(prev);
a = d; d = load4(row );
/* PNG requires a truncating average, so we can't just use _mm_avg_epu8 */
avg = _mm_avg_epu8(a,b);
/* ...but we can fix it up by subtracting off 1 if it rounded up. */
avg = _mm_sub_epi8(avg, _mm_and_si128(_mm_xor_si128(a,b),
_mm_set1_epi8(1)));
d = _mm_add_epi8(d, avg);
store4(row, d);
prev += 4;
row += 4;
rb -= 4;
}
}
/* Returns |x| for 16-bit lanes. */
static __m128i abs_i16(__m128i x) {
#if PNG_INTEL_SSE_IMPLEMENTATION >= 2
return _mm_abs_epi16(x);
#else
/* Read this all as, return x<0 ? -x : x.
* To negate two's complement, you flip all the bits then add 1.
*/
__m128i is_negative = _mm_cmplt_epi16(x, _mm_setzero_si128());
/* Flip negative lanes. */
x = _mm_xor_si128(x, is_negative);
/* +1 to negative lanes, else +0. */
x = _mm_sub_epi16(x, is_negative);
return x;
#endif
}
/* Bytewise c ? t : e. */
static __m128i if_then_else(__m128i c, __m128i t, __m128i e) {
#if PNG_INTEL_SSE_IMPLEMENTATION >= 3
return _mm_blendv_epi8(e,t,c);
#else
return _mm_or_si128(_mm_and_si128(c, t), _mm_andnot_si128(c, e));
#endif
}
void png_read_filter_row_paeth3_sse2(png_row_infop row_info, png_bytep row,
png_const_bytep prev)
{
/* Paeth tries to predict pixel d using the pixel to the left of it, a,
* and two pixels from the previous row, b and c:
* prev: c b
* row: a d
* The Paeth function predicts d to be whichever of a, b, or c is nearest to
* p=a+b-c.
*
* The first pixel has no left context, and so uses an Up filter, p = b.
* This works naturally with our main loop's p = a+b-c if we force a and c
* to zero.
* Here we zero b and d, which become c and a respectively at the start of
* the loop.
*/
size_t rb;
const __m128i zero = _mm_setzero_si128();
__m128i c, b = zero,
a, d = zero;
png_debug(1, "in png_read_filter_row_paeth3_sse2");
rb = row_info->rowbytes;
while (rb >= 4) {
/* It's easiest to do this math (particularly, deal with pc) with 16-bit
* intermediates.
*/
__m128i pa,pb,pc,smallest,nearest;
c = b; b = _mm_unpacklo_epi8(load4(prev), zero);
a = d; d = _mm_unpacklo_epi8(load4(row ), zero);
/* (p-a) == (a+b-c - a) == (b-c) */
pa = _mm_sub_epi16(b,c);
/* (p-b) == (a+b-c - b) == (a-c) */
pb = _mm_sub_epi16(a,c);
/* (p-c) == (a+b-c - c) == (a+b-c-c) == (b-c)+(a-c) */
pc = _mm_add_epi16(pa,pb);
pa = abs_i16(pa); /* |p-a| */
pb = abs_i16(pb); /* |p-b| */
pc = abs_i16(pc); /* |p-c| */
smallest = _mm_min_epi16(pc, _mm_min_epi16(pa, pb));
/* Paeth breaks ties favoring a over b over c. */
nearest = if_then_else(_mm_cmpeq_epi16(smallest, pa), a,
if_then_else(_mm_cmpeq_epi16(smallest, pb), b,
c));
/* Note `_epi8`: we need addition to wrap modulo 255. */
d = _mm_add_epi8(d, nearest);
store3(row, _mm_packus_epi16(d,d));
prev += 3;
row += 3;
rb -= 3;
}
if (rb > 0) {
/* It's easiest to do this math (particularly, deal with pc) with 16-bit
* intermediates.
*/
__m128i pa,pb,pc,smallest,nearest;
c = b; b = _mm_unpacklo_epi8(load3(prev), zero);
a = d; d = _mm_unpacklo_epi8(load3(row ), zero);
/* (p-a) == (a+b-c - a) == (b-c) */
pa = _mm_sub_epi16(b,c);
/* (p-b) == (a+b-c - b) == (a-c) */
pb = _mm_sub_epi16(a,c);
/* (p-c) == (a+b-c - c) == (a+b-c-c) == (b-c)+(a-c) */
pc = _mm_add_epi16(pa,pb);
pa = abs_i16(pa); /* |p-a| */
pb = abs_i16(pb); /* |p-b| */
pc = abs_i16(pc); /* |p-c| */
smallest = _mm_min_epi16(pc, _mm_min_epi16(pa, pb));
/* Paeth breaks ties favoring a over b over c. */
nearest = if_then_else(_mm_cmpeq_epi16(smallest, pa), a,
if_then_else(_mm_cmpeq_epi16(smallest, pb), b,
c));
/* Note `_epi8`: we need addition to wrap modulo 255. */
d = _mm_add_epi8(d, nearest);
store3(row, _mm_packus_epi16(d,d));
prev += 3;
row += 3;
rb -= 3;
}
}
void png_read_filter_row_paeth4_sse2(png_row_infop row_info, png_bytep row,
png_const_bytep prev)
{
/* Paeth tries to predict pixel d using the pixel to the left of it, a,
* and two pixels from the previous row, b and c:
* prev: c b
* row: a d
* The Paeth function predicts d to be whichever of a, b, or c is nearest to
* p=a+b-c.
*
* The first pixel has no left context, and so uses an Up filter, p = b.
* This works naturally with our main loop's p = a+b-c if we force a and c
* to zero.
* Here we zero b and d, which become c and a respectively at the start of
* the loop.
*/
size_t rb;
const __m128i zero = _mm_setzero_si128();
__m128i pa,pb,pc,smallest,nearest;
__m128i c, b = zero,
a, d = zero;
png_debug(1, "in png_read_filter_row_paeth4_sse2");
rb = row_info->rowbytes+4;
while (rb > 4) {
/* It's easiest to do this math (particularly, deal with pc) with 16-bit
* intermediates.
*/
c = b; b = _mm_unpacklo_epi8(load4(prev), zero);
a = d; d = _mm_unpacklo_epi8(load4(row ), zero);
/* (p-a) == (a+b-c - a) == (b-c) */
pa = _mm_sub_epi16(b,c);
/* (p-b) == (a+b-c - b) == (a-c) */
pb = _mm_sub_epi16(a,c);
/* (p-c) == (a+b-c - c) == (a+b-c-c) == (b-c)+(a-c) */
pc = _mm_add_epi16(pa,pb);
pa = abs_i16(pa); /* |p-a| */
pb = abs_i16(pb); /* |p-b| */
pc = abs_i16(pc); /* |p-c| */
smallest = _mm_min_epi16(pc, _mm_min_epi16(pa, pb));
/* Paeth breaks ties favoring a over b over c. */
nearest = if_then_else(_mm_cmpeq_epi16(smallest, pa), a,
if_then_else(_mm_cmpeq_epi16(smallest, pb), b,
c));
/* Note `_epi8`: we need addition to wrap modulo 255. */
d = _mm_add_epi8(d, nearest);
store4(row, _mm_packus_epi16(d,d));
prev += 4;
row += 4;
rb -= 4;
}
}
#endif /* PNG_INTEL_SSE_IMPLEMENTATION > 0 */
#endif /* READ */