Enabling SSE support

Copyright (c) 2016 Google, Inc.
Written by Mike Klein, Matt Sarett

This INSTALL file written by Glenn Randers-Pehrson, 2016.

If you have moved intel_init.c and filter_sse2_intrinsics.c to a different
directory, be sure to update the '#include "../../pngpriv.h"' line in both
files if necessary to point to the correct relative location of pngpriv.h
with respect to the new location of those files.

To enable SSE support in libpng, follow the instructions in I, II, or III,
below:

I. Using patched "configure" scripts:

First, apply intel_sse.patch in your build directory.

   patch -i contrib/intel/intel_sse.patch -p1

Then, if you are not building in a new GIT clone, e.g., in a tar
distribution, remove any existing pre-built configure scripts:

   ./configure --enable-maintainer-mode
   make maintainer-clean
   ./autogen.sh --maintainer --clean

Finally, configure libpng with -DPNG_INTEL_SSE in CPPFLAGS:

   ./autogen.sh --maintainer
   CPPFLAGS="-DPNG_INTEL_SSE" ./configure [options]
   make

II. Using a custom makefile:

If you are using a custom makefile makefile, you will have to update it
manually to include contrib/intel/*.o in the dependencies, and to define
PNG_INTEL_SSE.

III. Using manually updated "configure" scripts:

If you prefer, manually edit configure.ac and Makefile.am, following the
instructions below, then follow the instructions in section II of INSTALL
in the main libpng directory, then configure libpng with -DPNG_INTEL_SSE
in CPPFLAGS.

1. Insert the following lines above the copyright line near the top of
configure.ac:

-----------------cut----------------
# Copyright (c) 2016 Google, Inc.
# Written by Mike Klein and Matt Sarett
# Derived from the ARM supporting code in libpng/configure.ac, which was
-----------------cut----------------

2. Add the following code to configure.ac under HOST SPECIFIC OPTIONS
directly beneath the section for ARM:

-----------------cut----------------
# INTEL
# =====
#
# INTEL SSE (SIMD) support.

AC_ARG_ENABLE([intel-sse],
   AS_HELP_STRING([[[--enable-intel-sse]]],
      [Enable Intel SSE optimizations: =no/off, yes/on:]
      [no/off: disable the optimizations;]
      [yes/on: enable the optimizations.]
      [If not specified: determined by the compiler.]),
   [case "$enableval" in
      no|off)
         # disable the default enabling:
         AC_DEFINE([PNG_INTEL_SSE_OPT], [0],
                   [Disable Intel SSE optimizations])
         # Prevent inclusion of the assembler files below:
         enable_intel_sse=no;;
      yes|on)
         AC_DEFINE([PNG_INTEL_SSE_OPT], [1],
                   [Enable Intel SSE optimizations]);;
      *)
         AC_MSG_ERROR([--enable-intel-sse=${enable_intel_sse}: invalid value])
   esac])

# Add Intel specific files to all builds where the host_cpu is Intel ('x86*')
# or where Intel optimizations were explicitly requested (this allows a
# fallback if a future host CPU does not match 'x86*')
AM_CONDITIONAL([PNG_INTEL_SSE],
   [test "$enable_intel_sse" != 'no' &&
    case "$host_cpu" in
      i?86|x86_64) :;;
      *)    test "$enable_intel_sse" != '';;
    esac])
-----------------cut----------------

3. Insert the following lines above the copyright line near the top of
Makefile.am:

-----------------cut----------------
# Copyright (c) 2016 Google, Inc.
# Written by Mike Klein and Matt Sarett
# Derived from the ARM supporting code in libpng/configure.ac, which was
-----------------cut----------------

4. Add the following code to Makefile.am under HOST SPECIFIC OPTIONS
directly beneath the "if PNG_ARM_NEON ... endif" statement:

-----------------cut----------------
if PNG_INTEL_SSE
libpng@PNGLIB_MAJOR@@PNGLIB_MINOR@_la_SOURCES += contrib/intel/intel_init.c\
    contrib/intel/filter_sse2_intrinsics.c
endif
-----------------cut----------------

5. Add the following lines to pngpriv.h, following the PNG_ARM_NEON_OPT
code:

-----------------cut----------------
#ifndef PNG_INTEL_SSE_OPT
#   ifdef PNG_INTEL_SSE
      /* Only check for SSE if the build configuration has been modified to
       * enable SSE optimizations.  This means that these optimizations will
       * be off by default.  See contrib/intel for more details.
       */
#     if defined(__SSE4_1__) || defined(__AVX__) || defined(__SSSE3__) || \
       defined(__SSE2__) || defined(_M_X64) || defined(_M_AMD64) || \
       (defined(_M_IX86_FP) && _M_IX86_FP >= 2)
#         define PNG_INTEL_SSE_OPT 1
#      endif
#   endif
#endif

#if PNG_INTEL_SSE_OPT > 0
#   ifndef PNG_INTEL_SSE_IMPLEMENTATION
#      if defined(__SSE4_1__) || defined(__AVX__)
          /* We are not actually using AVX, but checking for AVX is the best
             way we can detect SSE4.1 and SSSE3 on MSVC.
          */
#         define PNG_INTEL_SSE_IMPLEMENTATION 3
#      elif defined(__SSSE3__)
#         define PNG_INTEL_SSE_IMPLEMENTATION 2
#      elif defined(__SSE2__) || defined(_M_X64) || defined(_M_AMD64) || \
       (defined(_M_IX86_FP) && _M_IX86_FP >= 2)
#         define PNG_INTEL_SSE_IMPLEMENTATION 1
#      else
#         define PNG_INTEL_SSE_IMPLEMENTATION 0
#      endif
#   endif

#   if PNG_INTEL_SSE_IMPLEMENTATION > 0
#      define PNG_FILTER_OPTIMIZATIONS png_init_filter_functions_sse2
#   endif
#endif

-----------------cut----------------

5. Add the following lines to pngpriv.h, following the prototype for
png_read_filter_row_paeth4_neon:

-----------------cut----------------
PNG_INTERNAL_FUNCTION(void,png_read_filter_row_sub3_sse2,(png_row_infop
    row_info, png_bytep row, png_const_bytep prev_row),PNG_EMPTY);
PNG_INTERNAL_FUNCTION(void,png_read_filter_row_sub4_sse2,(png_row_infop
    row_info, png_bytep row, png_const_bytep prev_row),PNG_EMPTY);
PNG_INTERNAL_FUNCTION(void,png_read_filter_row_avg3_sse2,(png_row_infop
    row_info, png_bytep row, png_const_bytep prev_row),PNG_EMPTY);
PNG_INTERNAL_FUNCTION(void,png_read_filter_row_avg4_sse2,(png_row_infop
    row_info, png_bytep row, png_const_bytep prev_row),PNG_EMPTY);
PNG_INTERNAL_FUNCTION(void,png_read_filter_row_paeth3_sse2,(png_row_infop
    row_info, png_bytep row, png_const_bytep prev_row),PNG_EMPTY);
PNG_INTERNAL_FUNCTION(void,png_read_filter_row_paeth4_sse2,(png_row_infop
    row_info, png_bytep row, png_const_bytep prev_row),PNG_EMPTY);

-----------------cut----------------