contrib/intel/intel_init.c

/* intel_init.c - SSE2 optimized filter functions
 *
 * Copyright (c) 2016 Google, Inc.
 *
 * Last changed in libpng 1.6.22 [(PENDING RELEASE)]
 *
 * This code is released under the libpng license.
 * For conditions of distribution and use, see the disclaimer
 * and license in png.h
 */

#include "../../pngpriv.h"

#ifdef PNG_READ_SUPPORTED
#if PNG_INTEL_SSE_IMPLEMENTATION > 0

void
png_init_filter_functions_sse2(png_structp pp, unsigned int bpp)
{
   // The techniques used to implement each of these filters in SSE operate on
   // one pixel at a time.
   // So they generally speed up 3bpp images about 3x, 4bpp images about 4x.
   // They can scale up to 6 and 8 bpp images and down to 2 bpp images, 
   // but they'd not likely have any benefit for 1bpp images.
   // Most of these can be implemented using only MMX and 64-bit registers,
   // but they end up a bit slower than using the equally-ubiquitous SSE2.
   if (bpp == 3)
   {
      pp->read_filter[PNG_FILTER_VALUE_SUB-1] = png_read_filter_row_sub3_sse2;
      pp->read_filter[PNG_FILTER_VALUE_AVG-1] = png_read_filter_row_avg3_sse2;
      pp->read_filter[PNG_FILTER_VALUE_PAETH-1] =
         png_read_filter_row_paeth3_sse2;
   }
   else if (bpp == 4)
   {
      pp->read_filter[PNG_FILTER_VALUE_SUB-1] = png_read_filter_row_sub4_sse2;
      pp->read_filter[PNG_FILTER_VALUE_AVG-1] = png_read_filter_row_avg4_sse2;
      pp->read_filter[PNG_FILTER_VALUE_PAETH-1] =
          png_read_filter_row_paeth4_sse2;
   }

   // No need optimize PNG_FILTER_VALUE_UP.  The compiler should autovectorize.
}

#endif /* PNG_INTEL_SSE_IMPLEMENTATION > 0 */
#endif /* PNG_READ_SUPPORTED */