tor-browser

ImageScalingSSE2.cpp (12890B)

---

/* -*- 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
* 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::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