Update libpng to 1.6.22beta

src/codec/SkPngFilters.cpp

-/*
- * Copyright 2016 Google Inc.
- *
- * Use of this source code is governed by a BSD-style license that can be
- * found in the LICENSE file.
- */
-
-#include "SkPngFilters.h"
-
-// Functions in this file look at most 3 pixels (a,b,c) to predict the fourth (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.  (Up also exists, predicting d=b.)
-
-#if defined(__SSE2__)
-
-    static __m128i load3(const void* p) {
-        uint32_t packed;
-        memcpy(&packed, p, 3);
-        return _mm_cvtsi32_si128(packed);
-    }
-
-    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, 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;
-        }
-    }
-
-    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.
-        __m128i a, d = _mm_setzero_si128();
-
-        int rb = row_info->rowbytes;
-        while (rb > 0) {
-            a = d; d = load4(row);
-            d = _mm_add_epi8(d, a);
-            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 );
-
-            // 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;
-        }
-    }
-
-    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
-        // 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 = 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);
-            // ...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 defined(__SSSE3__)
-        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());
-        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 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
-    }
-
-    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
-        //   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.
-        const __m128i zero = _mm_setzero_si128();
-        __m128i c, b = zero,
-                a, d = zero;
-
-        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(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)
-
-            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.
-            store3(row, _mm_packus_epi16(d,d));
-
-            prev += 3;
-            row  += 3;
-            rb   -= 3;
-        }
-    }
-
-    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.
-
-        // 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;
-
-        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