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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* 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
#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::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 mozilla::gfx