The Tor Browser: gfx/2d/ImageScalingSSE2.cpp@97036ab72558 (annotated)

gfx/2d/ImageScalingSSE2.cpp@97036ab72558 (annotated)

gfx/2d/ImageScalingSSE2.cpp

Tue, 06 Jan 2015 21:39:09 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Tue, 06 Jan 2015 21:39:09 +0100
branch: TOR_BUG_9701
changeset 8: 97036ab72558
permissions: -rw-r--r--

Conditionally force memory storage according to privacy.thirdparty.isolate;
This solves Tor bug #9701, complying with disk avoidance documented in
https://www.torproject.org/projects/torbrowser/design/#disk-avoidance.

 /* -*- 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 * 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));
     }
   }
 }
 }
 }

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gfx/2d/ImageScalingSSE2.cpp@97036ab72558 (annotated)

gfx/2d/ImageScalingSSE2.cpp