The Tor Browser: gfx/thebes/gfxAlphaRecoverySSE2.cpp@97036ab72558 (annotated)

gfx/thebes/gfxAlphaRecoverySSE2.cpp@97036ab72558 (annotated)

gfx/thebes/gfxAlphaRecoverySSE2.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: 4 -*-
  * 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 "gfxAlphaRecovery.h"
 #include "gfxImageSurface.h"
 #include "nsRect.h"
 #include <emmintrin.h>
 // This file should only be compiled on x86 and x64 systems.  Additionally,
 // you'll need to compile it with -msse2 if you're using GCC on x86.
 #if defined(_MSC_VER) && (defined(_M_IX86) || defined(_M_AMD64))
 __declspec(align(16)) static uint32_t greenMaski[] =
     { 0x0000ff00, 0x0000ff00, 0x0000ff00, 0x0000ff00 };
 __declspec(align(16)) static uint32_t alphaMaski[] =
     { 0xff000000, 0xff000000, 0xff000000, 0xff000000 };
 #elif defined(__GNUC__) && (defined(__i386__) || defined(__x86_64__))
 static uint32_t greenMaski[] __attribute__ ((aligned (16))) =
     { 0x0000ff00, 0x0000ff00, 0x0000ff00, 0x0000ff00 };
 static uint32_t alphaMaski[] __attribute__ ((aligned (16))) =
     { 0xff000000, 0xff000000, 0xff000000, 0xff000000 };
 #elif defined(__SUNPRO_CC) && (defined(__i386) || defined(__x86_64__))
 #pragma align 16 (greenMaski, alphaMaski)
 static uint32_t greenMaski[] = { 0x0000ff00, 0x0000ff00, 0x0000ff00, 0x0000ff00 };
 static uint32_t alphaMaski[] = { 0xff000000, 0xff000000, 0xff000000, 0xff000000 };
 #endif
 bool
 gfxAlphaRecovery::RecoverAlphaSSE2(gfxImageSurface* blackSurf,
                                    const gfxImageSurface* whiteSurf)
 {
     gfxIntSize size = blackSurf->GetSize();
     if (size != whiteSurf->GetSize() ||
         (blackSurf->Format() != gfxImageFormat::ARGB32 &&
          blackSurf->Format() != gfxImageFormat::RGB24) ||
         (whiteSurf->Format() != gfxImageFormat::ARGB32 &&
          whiteSurf->Format() != gfxImageFormat::RGB24))
         return false;
     blackSurf->Flush();
     whiteSurf->Flush();
     unsigned char* blackData = blackSurf->Data();
     unsigned char* whiteData = whiteSurf->Data();
     if ((NS_PTR_TO_UINT32(blackData) & 0xf) != (NS_PTR_TO_UINT32(whiteData) & 0xf) ||
         (blackSurf->Stride() - whiteSurf->Stride()) & 0xf) {
         // Cannot keep these in alignment.
         return false;
     }
     __m128i greenMask = _mm_load_si128((__m128i*)greenMaski);
     __m128i alphaMask = _mm_load_si128((__m128i*)alphaMaski);
     for (int32_t i = 0; i < size.height; ++i) {
         int32_t j = 0;
         // Loop single pixels until at 4 byte alignment.
         while (NS_PTR_TO_UINT32(blackData) & 0xf && j < size.width) {
             *((uint32_t*)blackData) =
                 RecoverPixel(*reinterpret_cast<uint32_t*>(blackData),
                              *reinterpret_cast<uint32_t*>(whiteData));
             blackData += 4;
             whiteData += 4;
             j++;
         }
         // This extra loop allows the compiler to do some more clever registry
         // management and makes it about 5% faster than with only the 4 pixel
         // at a time loop.
         for (; j < size.width - 8; j += 8) {
             __m128i black1 = _mm_load_si128((__m128i*)blackData);
             __m128i white1 = _mm_load_si128((__m128i*)whiteData);
             __m128i black2 = _mm_load_si128((__m128i*)(blackData + 16));
             __m128i white2 = _mm_load_si128((__m128i*)(whiteData + 16));
             // Execute the same instructions as described in RecoverPixel, only
             // using an SSE2 packed saturated subtract.
             white1 = _mm_subs_epu8(white1, black1);
             white2 = _mm_subs_epu8(white2, black2);
             white1 = _mm_subs_epu8(greenMask, white1);
             white2 = _mm_subs_epu8(greenMask, white2);
             // Producing the final black pixel in an XMM register and storing
             // that is actually faster than doing a masked store since that
             // does an unaligned storage. We have the black pixel in a register
             // anyway.
             black1 = _mm_andnot_si128(alphaMask, black1);
             black2 = _mm_andnot_si128(alphaMask, black2);
             white1 = _mm_slli_si128(white1, 2);
             white2 = _mm_slli_si128(white2, 2);
             white1 = _mm_and_si128(alphaMask, white1);
             white2 = _mm_and_si128(alphaMask, white2);
             black1 = _mm_or_si128(white1, black1);
             black2 = _mm_or_si128(white2, black2);
             _mm_store_si128((__m128i*)blackData, black1);
             _mm_store_si128((__m128i*)(blackData + 16), black2);
             blackData += 32;
             whiteData += 32;
         }
         for (; j < size.width - 4; j += 4) {
             __m128i black = _mm_load_si128((__m128i*)blackData);
             __m128i white = _mm_load_si128((__m128i*)whiteData);
             white = _mm_subs_epu8(white, black);
             white = _mm_subs_epu8(greenMask, white);
             black = _mm_andnot_si128(alphaMask, black);
             white = _mm_slli_si128(white, 2);
             white = _mm_and_si128(alphaMask, white);
             black = _mm_or_si128(white, black);
             _mm_store_si128((__m128i*)blackData, black);
             blackData += 16;
             whiteData += 16;
         }
         // Loop single pixels until we're done.
         while (j < size.width) {
             *((uint32_t*)blackData) =
                 RecoverPixel(*reinterpret_cast<uint32_t*>(blackData),
                              *reinterpret_cast<uint32_t*>(whiteData));
             blackData += 4;
             whiteData += 4;
             j++;
         }
         blackData += blackSurf->Stride() - j * 4;
         whiteData += whiteSurf->Stride() - j * 4;
     }
     blackSurf->MarkDirty();
     return true;
 }
 static int32_t
 ByteAlignment(int32_t aAlignToLog2, int32_t aX, int32_t aY=0, int32_t aStride=1)
 {
     return (aX + aStride * aY) & ((1 << aAlignToLog2) - 1);
 }
 /*static*/ nsIntRect
 gfxAlphaRecovery::AlignRectForSubimageRecovery(const nsIntRect& aRect,
                                                gfxImageSurface* aSurface)
 {
     NS_ASSERTION(gfxImageFormat::ARGB32 == aSurface->Format(),
                  "Thebes grew support for non-ARGB32 COLOR_ALPHA?");
     static const int32_t kByteAlignLog2 = GoodAlignmentLog2();
     static const int32_t bpp = 4;
     static const int32_t pixPerAlign = (1 << kByteAlignLog2) / bpp;
     //
     // We're going to create a subimage of the surface with size
     // <sw,sh> for alpha recovery, and want a SIMD fast-path.  The
     // rect <x,y, w,h> /needs/ to be redrawn, but it might not be
     // properly aligned for SIMD.  So we want to find a rect <x',y',
     // w',h'> that's a superset of what needs to be redrawn but is
     // properly aligned.  Proper alignment is
     //
     //   BPP * (x' + y' * sw) \cong 0         (mod ALIGN)
     //   BPP * w'             \cong BPP * sw  (mod ALIGN)
     //
     // (We assume the pixel at surface <0,0> is already ALIGN'd.)
     // That rect (obviously) has to fit within the surface bounds, and
     // we should also minimize the extra pixels redrawn only for
     // alignment's sake.  So we also want
     //
     //  minimize <x',y', w',h'>
     //   0 <= x' <= x
     //   0 <= y' <= y
     //   w <= w' <= sw
     //   h <= h' <= sh
     //
     // This is a messy integer non-linear programming problem, except
     // ... we can assume that ALIGN/BPP is a very small constant.  So,
     // brute force is viable.  The algorithm below will find a
     // solution if one exists, but isn't guaranteed to find the
     // minimum solution.  (For SSE2, ALIGN/BPP = 4, so it'll do at
     // most 64 iterations below).  In what's likely the common case,
     // an already-aligned rectangle, it only needs 1 iteration.
     //
     // Is this alignment worth doing?  Recovering alpha will take work
     // proportional to w*h (assuming alpha recovery computation isn't
     // memory bound).  This analysis can lead to O(w+h) extra work
     // (with small constants).  In exchange, we expect to shave off a
     // ALIGN/BPP constant by using SIMD-ized alpha recovery.  So as
     // w*h diverges from w+h, the win factor approaches ALIGN/BPP.  We
     // only really care about the w*h >> w+h case anyway; others
     // should be fast enough even with the overhead.  (Unless the cost
     // of repainting the expanded rect is high, but in that case
     // SIMD-ized alpha recovery won't make a difference so this code
     // shouldn't be called.)
     //
     gfxIntSize surfaceSize = aSurface->GetSize();
     const int32_t stride = bpp * surfaceSize.width;
     if (stride != aSurface->Stride()) {
         NS_WARNING("Unexpected stride, falling back on slow alpha recovery");
         return aRect;
     }
     const int32_t x = aRect.x, y = aRect.y, w = aRect.width, h = aRect.height;
     const int32_t r = x + w;
     const int32_t sw = surfaceSize.width;
     const int32_t strideAlign = ByteAlignment(kByteAlignLog2, stride);
     // The outer two loops below keep the rightmost (|r| above) and
     // bottommost pixels in |aRect| fixed wrt <x,y>, to ensure that we
     // return only a superset of the original rect.  These loops
     // search for an aligned top-left pixel by trying to expand <x,y>
     // left and up by <dx,dy> pixels, respectively.
     //
     // Then if a properly-aligned top-left pixel is found, the
     // innermost loop tries to find an aligned stride by moving the
     // rightmost pixel rightward by dr.
     int32_t dx, dy, dr;
     for (dy = 0; (dy < pixPerAlign) && (y - dy >= 0); ++dy) {
         for (dx = 0; (dx < pixPerAlign) && (x - dx >= 0); ++dx) {
             if (0 != ByteAlignment(kByteAlignLog2,
                                    bpp * (x - dx), y - dy, stride)) {
                 continue;
             }
             for (dr = 0; (dr < pixPerAlign) && (r + dr <= sw); ++dr) {
                 if (strideAlign == ByteAlignment(kByteAlignLog2,
                                                  bpp * (w + dr + dx))) {
                     goto FOUND_SOLUTION;
                 }
             }
         }
     }
     // Didn't find a solution.
     return aRect;
 FOUND_SOLUTION:
     nsIntRect solution = nsIntRect(x - dx, y - dy, w + dr + dx, h + dy);
     NS_ABORT_IF_FALSE(nsIntRect(0, 0, sw, surfaceSize.height).Contains(solution),
                       "'Solution' extends outside surface bounds!");
     return solution;
 }

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gfx/thebes/gfxAlphaRecoverySSE2.cpp@97036ab72558 (annotated)

gfx/thebes/gfxAlphaRecoverySSE2.cpp