Y2K compliance in libpng:

   =========================

      December 29, 2016

      Since the PNG Development group is an ad-hoc body, we can't make

      an official declaration.

      This is your unofficial assurance that libpng from version 0.71 and

      upward through 1.2.57 are Y2K compliant.  It is my belief that earlier

      versions were also Y2K compliant.

      Libpng only has three year fields.  One is a 2-byte unsigned integer

      that will hold years up to 65535.  The other two hold the date in text

      format, and will hold years up to 9999.

      The integer is

          "png_uint_16 year" in png_time_struct.

      The strings are

          "png_charp time_buffer" in png_struct and

          "near_time_buffer", which is a local character string in png.c.

      There are seven time-related functions:

          png_convert_to_rfc_1123() in png.c

            (formerly png_convert_to_rfc_1152() in error)

          png_convert_from_struct_tm() in pngwrite.c, called in pngwrite.c

          png_convert_from_time_t() in pngwrite.c

          png_get_tIME() in pngget.c

          png_handle_tIME() in pngrutil.c, called in pngread.c

          png_set_tIME() in pngset.c

          png_write_tIME() in pngwutil.c, called in pngwrite.c

      All appear to handle dates properly in a Y2K environment.  The

      png_convert_from_time_t() function calls gmtime() to convert from system

      clock time, which returns (year - 1900), which we properly convert to

      the full 4-digit year.  There is a possibility that applications using

      libpng are not passing 4-digit years into the png_convert_to_rfc_1123()

      function, or that they are incorrectly passing only a 2-digit year

      instead of "year - 1900" into the png_convert_from_struct_tm() function,

      but this is not under our control.  The libpng documentation has always

      stated that it works with 4-digit years, and the APIs have been

      documented as such.

      The tIME chunk itself is also Y2K compliant.  It uses a 2-byte unsigned

      integer to hold the year, and can hold years as large as 65535.

      zlib, upon which libpng depends, is also Y2K compliant.  It contains

      no date-related code.

         Glenn Randers-Pehrson

         libpng maintainer

         PNG Development Group