Known bugs and suggested enhancements in libpng-1.0.8

1. July 2, 2000 -- BUG -- pnggccrd.c

   The png_read_filter() function has still not been fully converted and
   will not compile under gcc-2.95.2; it is currently ifdef'ed out.

   STATUS: Under investigation.  Experts on MMX assembler code are
   invited to help with the debugging.  Note that pngvcrd.c works fine.

2. March 15, 1998 -- OPTIMIZATION -- Kevin Bracey

   Loops need to be optimized everywhere

   Make them count down instead of up -- Kevin Bracey

   Optimizing compilers don't need this, and making
   the change would be error prone -- Tom Lane, Glenn R-P

   Question whether i-- or --i is better.

   STATUS: Under investigation, postponed until after
   libpng-2.0.0.  About 160 loops will be turned around
   in libpng-2.0.x betaxx, for testing.

3. July 4, 1998 -- ENHANCEMENT -- Glenn R-P

   libpng-1.0.5 and earlier transform colors to gamma=1.0 space for
   merging with background, and then back to the image's gamma.  The
   bit_depth of the intermediate (gamma=1.0) representation is probably
   not sufficient.  In the typical gamma=1/2.2 situation, the linear
   pixels need about 4 more bits than the gamma-encoded ones, to avoid
   loss of precision.  A similar situation exists with the rgb_to_gray
   operation.

   STATUS: under development.

4. September 1999 -- ENHANCEMENT --

   It should be possible to use libpng without floating-point aritmetic.

   STATUS: Under investigation, implementation postponed until after
   libpng-2.0.0.

   Much of this was completed in libpng-1.0.6, but gamma compensation
   is not yet done in fixed-point arithmetic.