POINTER_INDEXING was a build configuration option that we maintained
in order to work around a gcc 2.7.2.2 code generation bug (circa 1997).
This provided array-indexing fallback loops in `png_write_PLTE` and
`png_write_sPLT`.
Unfortunately, the fallback paths were effectively untested dead code
in every default build, and have been a recurring source of latent bugs.
(See commit 48800443eb in pnggroup/libpng#801 and commit f27592a0cd in
libpng 1.5.2rc02).
No compiler in current use requires this accommodation.
The purpose of this feature was to optionally prepend standardized
numbers to error and warning messages. The ERROR_NUMBERS feature was
first drafted in libpng-1.2.0 and further developed in libpng-1.4.0;
and yet, it was always disabled by default, and never completed.
In the light of a recent report concerning the security hazards arising
from enabling this code in custom libpng builds, we think it's best to
simply remove all the code written to support this feature.
Reported-by: Tobias Stoeckmann <tobias@stoeckmann.org>
Signed-off-by: Cosmin Truta <ctruta@gmail.com>
Considering that pnglibconf is a whole mini-system for configuring and
building libpng, it should be placed in its own dedicated subdirectory.
Any future additions, including tests and documentation, should go into
this subdirectory.
One exception: pnglibconf.h.prebuilt is moved to the top-level source
directory, where pnglibconf.h would be. This follows the organization
pattern typically used with the "*.in" files, for example.
All references to the pnglibconf artifacts, found in machine-readable
code and in human-readable comments, are updated accordingly.
