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+/* -*- Mode: C++; tab-width: 20; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "ImageScaling.h"
+#include "mozilla/Attributes.h"
+
+#include "SSEHelpers.h"
+
+/* The functions below use the following system for averaging 4 pixels:
+ *
+ * The first observation is that a half-adder is implemented as follows:
+ * R = S + 2C or in the case of a and b (a ^ b) + ((a & b) << 1);
+ *
+ * This can be trivially extended to three pixels by observaring that when
+ * doing (a ^ b ^ c) as the sum, the carry is simply the bitwise-or of the
+ * carries of the individual numbers, since the sum of 3 bits can only ever
+ * have a carry of one.
+ *
+ * We then observe that the average is then ((carry << 1) + sum) >> 1, or,
+ * assuming eliminating overflows and underflows, carry + (sum >> 1).
+ *
+ * We now average our existing sum with the fourth number, so we get:
+ * sum2 = (sum + d) >> 1 or (sum >> 1) + (d >> 1).
+ *
+ * We now observe that our sum has been moved into place relative to the
+ * carry, so we can now average with the carry to get the final 4 input
+ * average: avg = (sum2 + carry) >> 1;
+ *
+ * Or to reverse the proof:
+ * avg = ((sum >> 1) + carry + d >> 1) >> 1
+ * avg = ((a + b + c) >> 1 + d >> 1) >> 1
+ * avg = ((a + b + c + d) >> 2)
+ *
+ * An additional fact used in the SSE versions is the concept that we can
+ * trivially convert a rounded average to a truncated average:
+ *
+ * We have:
+ * f(a, b) = (a + b + 1) >> 1
+ *
+ * And want:
+ * g(a, b) = (a + b) >> 1
+ *
+ * Observe:
+ * ~f(~a, ~b) == ~((~a + ~b + 1) >> 1)
+ * == ~((-a - 1 + -b - 1 + 1) >> 1)
+ * == ~((-a - 1 + -b) >> 1)
+ * == ~((-(a + b) - 1) >> 1)
+ * == ~((~(a + b)) >> 1)
+ * == (a + b) >> 1
+ * == g(a, b)
+ */
+
+MOZ_ALWAYS_INLINE __m128i _mm_not_si128(__m128i arg)
+{
+ __m128i minusone = _mm_set1_epi32(0xffffffff);
+ return _mm_xor_si128(arg, minusone);
+}
+
+/* We have to pass pointers here, MSVC does not allow passing more than 3
+ * __m128i arguments on the stack. And it does not allow 16-byte aligned
+ * stack variables. This inlines properly on MSVC 2010. It does -not- inline
+ * with just the inline directive.
+ */
+MOZ_ALWAYS_INLINE __m128i avg_sse2_8x2(__m128i *a, __m128i *b, __m128i *c, __m128i *d)
+{
+#define shuf1 _MM_SHUFFLE(2, 0, 2, 0)
+#define shuf2 _MM_SHUFFLE(3, 1, 3, 1)
+
+// This cannot be an inline function as the __Imm argument to _mm_shuffle_ps
+// needs to be a compile time constant.
+#define shuffle_si128(arga, argb, imm) \
+ _mm_castps_si128(_mm_shuffle_ps(_mm_castsi128_ps((arga)), _mm_castsi128_ps((argb)), (imm)));
+
+ __m128i t = shuffle_si128(*a, *b, shuf1);
+ *b = shuffle_si128(*a, *b, shuf2);
+ *a = t;
+ t = shuffle_si128(*c, *d, shuf1);
+ *d = shuffle_si128(*c, *d, shuf2);
+ *c = t;
+
+#undef shuf1
+#undef shuf2
+#undef shuffle_si128
+
+ __m128i sum = _mm_xor_si128(*a, _mm_xor_si128(*b, *c));
+
+ __m128i carry = _mm_or_si128(_mm_and_si128(*a, *b), _mm_or_si128(_mm_and_si128(*a, *c), _mm_and_si128(*b, *c)));
+
+ sum = _mm_avg_epu8(_mm_not_si128(sum), _mm_not_si128(*d));
+
+ return _mm_not_si128(_mm_avg_epu8(sum, _mm_not_si128(carry)));
+}
+
+MOZ_ALWAYS_INLINE __m128i avg_sse2_4x2_4x1(__m128i a, __m128i b)
+{
+ return _mm_not_si128(_mm_avg_epu8(_mm_not_si128(a), _mm_not_si128(b)));
+}
+
+MOZ_ALWAYS_INLINE __m128i avg_sse2_8x1_4x1(__m128i a, __m128i b)
+{
+ __m128i t = _mm_castps_si128(_mm_shuffle_ps(_mm_castsi128_ps(a), _mm_castsi128_ps(b), _MM_SHUFFLE(3, 1, 3, 1)));
+ b = _mm_castps_si128(_mm_shuffle_ps(_mm_castsi128_ps(a), _mm_castsi128_ps(b), _MM_SHUFFLE(2, 0, 2, 0)));
+ a = t;
+
+ return _mm_not_si128(_mm_avg_epu8(_mm_not_si128(a), _mm_not_si128(b)));
+}
+
+MOZ_ALWAYS_INLINE uint32_t Avg2x2(uint32_t a, uint32_t b, uint32_t c, uint32_t d)
+{
+ uint32_t sum = a ^ b ^ c;
+ uint32_t carry = (a & b) | (a & c) | (b & c);
+
+ uint32_t mask = 0xfefefefe;
+
+ // Not having a byte based average instruction means we should mask to avoid
+ // underflow.
+ sum = (((sum ^ d) & mask) >> 1) + (sum & d);
+
+ return (((sum ^ carry) & mask) >> 1) + (sum & carry);
+}
+
+// Simple 2 pixel average version of the function above.
+MOZ_ALWAYS_INLINE uint32_t Avg2(uint32_t a, uint32_t b)
+{
+ uint32_t sum = a ^ b;
+ uint32_t carry = (a & b);
+
+ uint32_t mask = 0xfefefefe;
+
+ return ((sum & mask) >> 1) + carry;
+}
+
+namespace mozilla {
+namespace gfx {
+
+void
+ImageHalfScaler::HalfImage2D_SSE2(uint8_t *aSource, int32_t aSourceStride,
+ const IntSize &aSourceSize, uint8_t *aDest,
+ uint32_t aDestStride)
+{
+ const int Bpp = 4;
+
+ for (int y = 0; y < aSourceSize.height; y += 2) {
+ __m128i *storage = (__m128i*)(aDest + (y / 2) * aDestStride);
+ int x = 0;
+ // Run a loop depending on alignment.
+ if (!(uintptr_t(aSource + (y * aSourceStride)) % 16) &&
+ !(uintptr_t(aSource + ((y + 1) * aSourceStride)) % 16)) {
+ for (; x < (aSourceSize.width - 7); x += 8) {
+ __m128i *upperRow = (__m128i*)(aSource + (y * aSourceStride + x * Bpp));
+ __m128i *lowerRow = (__m128i*)(aSource + ((y + 1) * aSourceStride + x * Bpp));
+
+ __m128i a = _mm_load_si128(upperRow);
+ __m128i b = _mm_load_si128(upperRow + 1);
+ __m128i c = _mm_load_si128(lowerRow);
+ __m128i d = _mm_load_si128(lowerRow + 1);
+
+ *storage++ = avg_sse2_8x2(&a, &b, &c, &d);
+ }
+ } else if (!(uintptr_t(aSource + (y * aSourceStride)) % 16)) {
+ for (; x < (aSourceSize.width - 7); x += 8) {
+ __m128i *upperRow = (__m128i*)(aSource + (y * aSourceStride + x * Bpp));
+ __m128i *lowerRow = (__m128i*)(aSource + ((y + 1) * aSourceStride + x * Bpp));
+
+ __m128i a = _mm_load_si128(upperRow);
+ __m128i b = _mm_load_si128(upperRow + 1);
+ __m128i c = loadUnaligned128(lowerRow);
+ __m128i d = loadUnaligned128(lowerRow + 1);
+
+ *storage++ = avg_sse2_8x2(&a, &b, &c, &d);
+ }
+ } else if (!(uintptr_t(aSource + ((y + 1) * aSourceStride)) % 16)) {
+ for (; x < (aSourceSize.width - 7); x += 8) {
+ __m128i *upperRow = (__m128i*)(aSource + (y * aSourceStride + x * Bpp));
+ __m128i *lowerRow = (__m128i*)(aSource + ((y + 1) * aSourceStride + x * Bpp));
+
+ __m128i a = loadUnaligned128((__m128i*)upperRow);
+ __m128i b = loadUnaligned128((__m128i*)upperRow + 1);
+ __m128i c = _mm_load_si128((__m128i*)lowerRow);
+ __m128i d = _mm_load_si128((__m128i*)lowerRow + 1);
+
+ *storage++ = avg_sse2_8x2(&a, &b, &c, &d);
+ }
+ } else {
+ for (; x < (aSourceSize.width - 7); x += 8) {
+ __m128i *upperRow = (__m128i*)(aSource + (y * aSourceStride + x * Bpp));
+ __m128i *lowerRow = (__m128i*)(aSource + ((y + 1) * aSourceStride + x * Bpp));
+
+ __m128i a = loadUnaligned128(upperRow);
+ __m128i b = loadUnaligned128(upperRow + 1);
+ __m128i c = loadUnaligned128(lowerRow);
+ __m128i d = loadUnaligned128(lowerRow + 1);
+
+ *storage++ = avg_sse2_8x2(&a, &b, &c, &d);
+ }
+ }
+
+ uint32_t *unalignedStorage = (uint32_t*)storage;
+ // Take care of the final pixels, we know there's an even number of pixels
+ // in the source rectangle. We use a 2x2 'simd' implementation for this.
+ //
+ // Potentially we only have to do this in the last row since overflowing
+ // 8 pixels in an earlier row would appear to be harmless as it doesn't
+ // touch invalid memory. Even when reading and writing to the same surface.
+ // in practice we only do this when doing an additional downscale pass, and
+ // in this situation we have unused stride to write into harmlessly.
+ // I do not believe the additional code complexity would be worth it though.
+ for (; x < aSourceSize.width; x += 2) {
+ uint8_t *upperRow = aSource + (y * aSourceStride + x * Bpp);
+ uint8_t *lowerRow = aSource + ((y + 1) * aSourceStride + x * Bpp);
+
+ *unalignedStorage++ = Avg2x2(*(uint32_t*)upperRow, *((uint32_t*)upperRow + 1),
+ *(uint32_t*)lowerRow, *((uint32_t*)lowerRow + 1));
+ }
+ }
+}
+
+void
+ImageHalfScaler::HalfImageVertical_SSE2(uint8_t *aSource, int32_t aSourceStride,
+ const IntSize &aSourceSize, uint8_t *aDest,
+ uint32_t aDestStride)
+{
+ for (int y = 0; y < aSourceSize.height; y += 2) {
+ __m128i *storage = (__m128i*)(aDest + (y / 2) * aDestStride);
+ int x = 0;
+ // Run a loop depending on alignment.
+ if (!(uintptr_t(aSource + (y * aSourceStride)) % 16) &&
+ !(uintptr_t(aSource + ((y + 1) * aSourceStride)) % 16)) {
+ for (; x < (aSourceSize.width - 3); x += 4) {
+ uint8_t *upperRow = aSource + (y * aSourceStride + x * 4);
+ uint8_t *lowerRow = aSource + ((y + 1) * aSourceStride + x * 4);
+
+ __m128i a = _mm_load_si128((__m128i*)upperRow);
+ __m128i b = _mm_load_si128((__m128i*)lowerRow);
+
+ *storage++ = avg_sse2_4x2_4x1(a, b);
+ }
+ } else if (!(uintptr_t(aSource + (y * aSourceStride)) % 16)) {
+ // This line doesn't align well.
+ for (; x < (aSourceSize.width - 3); x += 4) {
+ uint8_t *upperRow = aSource + (y * aSourceStride + x * 4);
+ uint8_t *lowerRow = aSource + ((y + 1) * aSourceStride + x * 4);
+
+ __m128i a = _mm_load_si128((__m128i*)upperRow);
+ __m128i b = loadUnaligned128((__m128i*)lowerRow);
+
+ *storage++ = avg_sse2_4x2_4x1(a, b);
+ }
+ } else if (!(uintptr_t(aSource + ((y + 1) * aSourceStride)) % 16)) {
+ for (; x < (aSourceSize.width - 3); x += 4) {
+ uint8_t *upperRow = aSource + (y * aSourceStride + x * 4);
+ uint8_t *lowerRow = aSource + ((y + 1) * aSourceStride + x * 4);
+
+ __m128i a = loadUnaligned128((__m128i*)upperRow);
+ __m128i b = _mm_load_si128((__m128i*)lowerRow);
+
+ *storage++ = avg_sse2_4x2_4x1(a, b);
+ }
+ } else {
+ for (; x < (aSourceSize.width - 3); x += 4) {
+ uint8_t *upperRow = aSource + (y * aSourceStride + x * 4);
+ uint8_t *lowerRow = aSource + ((y + 1) * aSourceStride + x * 4);
+
+ __m128i a = loadUnaligned128((__m128i*)upperRow);
+ __m128i b = loadUnaligned128((__m128i*)lowerRow);
+
+ *storage++ = avg_sse2_4x2_4x1(a, b);
+ }
+ }
+
+ uint32_t *unalignedStorage = (uint32_t*)storage;
+ // Take care of the final pixels, we know there's an even number of pixels
+ // in the source rectangle.
+ //
+ // Similar overflow considerations are valid as in the previous function.
+ for (; x < aSourceSize.width; x++) {
+ uint8_t *upperRow = aSource + (y * aSourceStride + x * 4);
+ uint8_t *lowerRow = aSource + ((y + 1) * aSourceStride + x * 4);
+
+ *unalignedStorage++ = Avg2(*(uint32_t*)upperRow, *(uint32_t*)lowerRow);
+ }
+ }
+}
+
+void
+ImageHalfScaler::HalfImageHorizontal_SSE2(uint8_t *aSource, int32_t aSourceStride,
+ const IntSize &aSourceSize, uint8_t *aDest,
+ uint32_t aDestStride)
+{
+ for (int y = 0; y < aSourceSize.height; y++) {
+ __m128i *storage = (__m128i*)(aDest + (y * aDestStride));
+ int x = 0;
+ // Run a loop depending on alignment.
+ if (!(uintptr_t(aSource + (y * aSourceStride)) % 16)) {
+ for (; x < (aSourceSize.width - 7); x += 8) {
+ __m128i* pixels = (__m128i*)(aSource + (y * aSourceStride + x * 4));
+
+ __m128i a = _mm_load_si128(pixels);
+ __m128i b = _mm_load_si128(pixels + 1);
+
+ *storage++ = avg_sse2_8x1_4x1(a, b);
+ }
+ } else {
+ for (; x < (aSourceSize.width - 7); x += 8) {
+ __m128i* pixels = (__m128i*)(aSource + (y * aSourceStride + x * 4));
+
+ __m128i a = loadUnaligned128(pixels);
+ __m128i b = loadUnaligned128(pixels + 1);
+
+ *storage++ = avg_sse2_8x1_4x1(a, b);
+ }
+ }
+
+ uint32_t *unalignedStorage = (uint32_t*)storage;
+ // Take care of the final pixels, we know there's an even number of pixels
+ // in the source rectangle.
+ //
+ // Similar overflow considerations are valid as in the previous function.
+ for (; x < aSourceSize.width; x += 2) {
+ uint32_t *pixels = (uint32_t*)(aSource + (y * aSourceStride + x * 4));
+
+ *unalignedStorage++ = Avg2(*pixels, *(pixels + 1));
+ }
+ }
+}
+
+} // namespace gfx
+} // namespace mozilla
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