Commits on Oct 10, 2024

1. This change updates support for target-specific code. …

   The change removes the need for build configuration of target specific
   code such as SIMD enhancements.
   
   The extensible framework is based on checks in the new file named
   pngtarget.h and allows per target description of requirements and
   capabilities using macros with the prefix PNG_TARGET_.  These macros are
   interpreted by the core libpng code in a target independent way.
   
   The PNG_TARGET_ prefixed macros describe the target specific
   implementation and document how to include it.  The actual inclusion of
   the code is done, at present, by a single target independent core file
   named pngsimd.c.
   
   This approach ensures that no special configuration in the build system
   is required on any system.  It is not required on a system which is
   compiling for the build host where we can reasonably assume that the
   compiler is correctly set up.  Neither is it required for cross builds
   so long as the toolchain is correctly set up.  In this case the
   toolchain means the cross build system and any ancilliary programs it
   requires.
   
   More details of the implementation are included in the source files
   named pngtarget.h and pngsimd.c.  These files document in C comments how
   additional target specific code might be added.
   
   The changes consist primarily of movement of target specific code from
   the core libpng source files to the existing target specific
   subdirectories such as the ones named intel and arm.  This isolates the
   code into the corresponding subdirectory and eliminates the requirement
   for changes across the libpng structure.
   
   As part of this the ARM processor NEON instruction set specific palette
   to RGB code has been generalised to allow implementation in other
   architectures.  The resultant updated version of the original (ARM Ltd)
   implementation has been moved to the subdirectory named arm.
   
   In addition some selected changes have been included to allow testing
   with higher warning levels than the typical compiler defaults.
   
   Signed-off-by: John Bowler <[email protected]>

   

   jbowler committed Oct 10, 2024
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