I didn't intend to distribute this but it leaked into the libpng16 source,
so here it is.

only one filter is a candidate for selection. This trades off code size (added
png_setup_*_row_only() functions) for speed.

The fixed size buffer for the file name being processed could have a byte
written beyond the end; a bug where the test was updated without changing the
size of the buffer.  This commit reduces the buffer to the system maximum.

png_getrowbytes could, in theory, return 0; probably only if there is a bug in
libpng but the code now checks.
Signed-off-by: NJohn Bowler <jbowler@acm.org>

In libpng 1.7 pngimage needs to check PNG_WRITE_PNG_SUPPORTED (new in 1.7), not
PNG_WRITE_SUPPORTED because png_write_png can be disabled without disabling
PNG_WRITE_SUPPORTED.  Copied the approach from 1.6 pngcp.c (so this still works
in 1.6 as well.)

Signed-off-by: NJohn Bowler <jbowler@acm.org>

If PNG_PNGCP_TIMING_SUPPORTED is defined maximal resolution CPU time logging of
png_read_png and png_write_png is enabled via the --time command line option.
This is not on by default but is enabled by contrib/conftests/pngcp.dfa
Signed-off-by: NJohn Bowler <jbowler@acm.org>

This adds pngcp to the build together with a pngcp.dfa configuration test; the
test revealed some configuration bugs which are fixed by corrections to the
_SUPPORTED macros.

pngcp builds on all tested configurations and a number of bugs have been fixed
to make this happen relative to the version in libpng 1.7 contrib/examples.
pngcp.dfa will have to be different for 1.7 but pngcp.c should work fine (not
yet tested).  pngcp itself is still missing a usage message; this is a
preliminary version, although since it behaves the same way as 'cp' most unoids
shouldn't have a problem using it correctly.
Signed-off-by: NJohn Bowler <jbowler@acm.org>

code in the PAETH decoder in pngrutil.c. Build with PNG_USE_ABS to use this.

The commit removes the three compile warning options from the individual project
files into the zlib.props globals (this should probably be renamed in 1.7).  It
increases the warning level from 4 to All and adds a list of the warnings which
need to be turned off.  This is semi-documentary; the intent is to tell users of
libpng which warnings have been examined and judged non-fixable at present.

The warning about structure padding *IS* fixable, but it is a signficant change
(moving structure members around).  It is currently partially fixed in 1.7, but
only partially.
Signed-off-by: NJohn Bowler <jbowler@acm.org>

The SKIP definition needs to come after the png.h include (see all the other .c
files in contrib/libtests) because it depends on PNG_LIBPNG_VER.  This commit
puts it in the correct place.
Signed-off-by: NJohn Bowler <jbowler@acm.org>

MSVC does not like (uInt) = -(unsigned) (i.e. as an initializer), but it is fine
with it if the conversion is explicitly invoked by a cast.
Signed-off-by: NJohn Bowler <jbowler@acm.org>

MSVC doesn't like '-(unsigned)', so replace it by 0U-(unsigned) (in 1.6).
Signed-off-by: NJohn Bowler <jbowler@acm.org>