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Unified Diff: src/codec/SkPngFilters.cpp

Issue 1699953002: Make png filter functions compatible with libpng (Closed) Base URL: https://skia.googlesource.com/skia.git@master
Patch Set: Return to Skia style Created 4 years, 10 months ago
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Index: src/codec/SkPngFilters.cpp
diff --git a/src/codec/SkPngFilters.cpp b/src/codec/SkPngFilters.cpp
index 472123fa15e6c6010eda52f1b37efd49ab06068b..2777939357556271feae34d129e4083f9c37ccd0 100644
--- a/src/codec/SkPngFilters.cpp
+++ b/src/codec/SkPngFilters.cpp
@@ -16,25 +16,43 @@
#if defined(__SSE2__)
- template <int bpp>
- static __m128i load(const void* p) {
- static_assert(bpp <= 4, "");
-
+ static __m128i load3(const void* p) {
uint32_t packed;
- memcpy(&packed, p, bpp);
+ memcpy(&packed, p, 3);
return _mm_cvtsi32_si128(packed);
}
- template <int bpp>
- static void store(void* p, __m128i v) {
- static_assert(bpp <= 4, "");
+ static __m128i load4(const void* p) {
+ return _mm_cvtsi32_si128(*(const int*)p);
+ }
+ static void store3(void* p, __m128i v) {
uint32_t packed = _mm_cvtsi128_si32(v);
- memcpy(p, &packed, bpp);
+ memcpy(p, &packed, 3);
+ }
+
+ static void store4(void* p, __m128i v) {
+ *(int*)p = _mm_cvtsi128_si32(v);
+ }
+
+ void sk_sub3_sse2(png_row_infop row_info, uint8_t* row, const uint8_t* 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.
+ __m128i a, d = _mm_setzero_si128();
+
+ int rb = row_info->rowbytes;
+ while (rb > 0) {
+ a = d; d = load3(row);
+ d = _mm_add_epi8(d, a);
+ store3(row, d);
+
+ row += 3;
+ rb -= 3;
+ }
}
- template <int bpp>
- static void sk_sub_sse2(png_row_infop row_info, uint8_t* row, const uint8_t*) {
+ void sk_sub4_sse2(png_row_infop row_info, uint8_t* row, const uint8_t* 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.
@@ -42,17 +60,44 @@
int rb = row_info->rowbytes;
while (rb > 0) {
- a = d; d = load<bpp>(row);
+ a = d; d = load4(row);
d = _mm_add_epi8(d, a);
- store<bpp>(row, d);
+ store4(row, d);
+
+ row += 4;
+ rb -= 4;
+ }
+ }
+
+ void sk_avg3_sse2(png_row_infop row_info, uint8_t* row, const uint8_t* 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.
+ const __m128i zero = _mm_setzero_si128();
+ __m128i b;
+ __m128i a, d = zero;
+
+ int rb = row_info->rowbytes;
+ while (rb > 0) {
+ b = load3(prev);
+ a = d; d = load3(row );
- row += bpp;
- rb -= bpp;
+ // PNG requires a truncating average here, so sadly we can't just use _mm_avg_epu8...
+ __m128i 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;
}
}
- template <int bpp>
- void sk_avg_sse2(png_row_infop row_info, uint8_t* row, const uint8_t* prev) {
+ void sk_avg4_sse2(png_row_infop row_info, uint8_t* row, const uint8_t* 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
@@ -63,8 +108,8 @@
int rb = row_info->rowbytes;
while (rb > 0) {
- b = load<bpp>(prev);
- a = d; d = load<bpp>(row );
+ b = load4(prev);
+ a = d; d = load4(row );
// PNG requires a truncating average here, so sadly we can't just use _mm_avg_epu8...
__m128i avg = _mm_avg_epu8(a,b);
@@ -72,11 +117,11 @@
avg = _mm_sub_epi8(avg, _mm_and_si128(_mm_xor_si128(a,b), _mm_set1_epi8(1)));
d = _mm_add_epi8(d, avg);
- store<bpp>(row, d);
+ store4(row, d);
- prev += bpp;
- row += bpp;
- rb -= bpp;
+ prev += 4;
+ row += 4;
+ rb -= 4;
}
}
@@ -88,23 +133,22 @@
// 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());
- x = _mm_xor_si128(x, is_negative); // Flip negative lanes.
- x = _mm_add_epi16(x, _mm_srli_epi16(is_negative, 15)); // +1 to negative lanes, else +0.
+ x = _mm_xor_si128(x, is_negative); // Flip negative lanes.
+ x = _mm_add_epi16(x, _mm_srli_epi16(is_negative, 15)); // +1 to negative lanes, else +0.
return x;
#endif
}
// Bytewise c ? t : e.
static __m128i if_then_else(__m128i c, __m128i t, __m128i e) {
- #if 0 && defined(__SSE4_1__) // Make sure we have a bot testing this before enabling.
+ #if defined(__SSE4_1__)
return _mm_blendv_epi8(e,t,c);
#else
return _mm_or_si128(_mm_and_si128(c, t), _mm_andnot_si128(c, e));
#endif
}
- template <int bpp>
- void sk_paeth_sse2(png_row_infop row_info, uint8_t* row, const uint8_t* prev) {
+ void sk_paeth3_sse2(png_row_infop row_info, uint8_t* row, const uint8_t* 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
@@ -121,9 +165,8 @@
int rb = row_info->rowbytes;
while (rb > 0) {
// It's easiest to do this math (particularly, deal with pc) with 16-bit intermediates.
- c = b; b = _mm_unpacklo_epi8(load<bpp>(prev), zero);
- a = d; d = _mm_unpacklo_epi8(load<bpp>(row ), zero);
-
+ c = b; b = _mm_unpacklo_epi8(load3(prev), zero);
+ a = d; d = _mm_unpacklo_epi8(load3(row ), zero);
__m128i pa = _mm_sub_epi16(b,c), // (p-a) == (a+b-c - a) == (b-c)
pb = _mm_sub_epi16(a,c), // (p-b) == (a+b-c - b) == (a-c)
pc = _mm_add_epi16(pa,pb); // (p-c) == (a+b-c - c) == (a+b-c-c) == (b-c)+(a-c)
@@ -140,33 +183,55 @@
c));
d = _mm_add_epi8(d, nearest); // Note `_epi8`: we need addition to wrap modulo 255.
- store<bpp>(row, _mm_packus_epi16(d,d));
+ store3(row, _mm_packus_epi16(d,d));
- prev += bpp;
- row += bpp;
- rb -= bpp;
+ prev += 3;
+ row += 3;
+ rb -= 3;
}
}
- void sk_sub3_sse2(png_row_infop row_info, uint8_t* row, const uint8_t* prev) {
- sk_sub_sse2<3>(row_info, row, prev);
- }
- void sk_sub4_sse2(png_row_infop row_info, uint8_t* row, const uint8_t* prev) {
- sk_sub_sse2<4>(row_info, row, prev);
- }
+ void sk_paeth4_sse2(png_row_infop row_info, uint8_t* row, const uint8_t* 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.
- void sk_avg3_sse2(png_row_infop row_info, uint8_t* row, const uint8_t* prev) {
- sk_avg_sse2<3>(row_info, row, prev);
- }
- void sk_avg4_sse2(png_row_infop row_info, uint8_t* row, const uint8_t* prev) {
- sk_avg_sse2<4>(row_info, row, prev);
- }
+ // 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.
+ const __m128i zero = _mm_setzero_si128();
+ __m128i c, b = zero,
+ a, d = zero;
- void sk_paeth3_sse2(png_row_infop row_info, uint8_t* row, const uint8_t* prev) {
- sk_paeth_sse2<3>(row_info, row, prev);
- }
- void sk_paeth4_sse2(png_row_infop row_info, uint8_t* row, const uint8_t* prev) {
- sk_paeth_sse2<4>(row_info, row, prev);
+ int rb = row_info->rowbytes;
+ while (rb > 0) {
+ // 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);
+ __m128i pa = _mm_sub_epi16(b,c), // (p-a) == (a+b-c - a) == (b-c)
+ pb = _mm_sub_epi16(a,c), // (p-b) == (a+b-c - b) == (a-c)
+ pc = _mm_add_epi16(pa,pb); // (p-c) == (a+b-c - c) == (a+b-c-c) == (b-c)+(a-c)
+
+ pa = abs_i16(pa); // |p-a|
+ pb = abs_i16(pb); // |p-b|
+ pc = abs_i16(pc); // |p-c|
+
+ __m128i smallest = _mm_min_epi16(pc, _mm_min_epi16(pa, pb));
+
+ // Paeth breaks ties favoring a over b over c.
+ __m128i nearest = if_then_else(_mm_cmpeq_epi16(smallest, pa), a,
+ if_then_else(_mm_cmpeq_epi16(smallest, pb), b,
+ c));
+
+ d = _mm_add_epi8(d, nearest); // Note `_epi8`: we need addition to wrap modulo 255.
+ store4(row, _mm_packus_epi16(d,d));
+
+ prev += 4;
+ row += 4;
+ rb -= 4;
+ }
}
#endif
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