src/png/Y2KINFO

   1    Y2K compliance in libpng:
   2    =========================
   3
   4       December 18, 2008
   5
   6       Since the PNG Development group is an ad-hoc body, we can't make
   7       an official declaration.
   8
   9       This is your unofficial assurance that libpng from version 0.71 and
  10       upward through 1.2.34 are Y2K compliant.  It is my belief that earlier
  11       versions were also Y2K compliant.
  12
  13       Libpng only has three year fields.  One is a 2-byte unsigned integer
  14       that will hold years up to 65535.  The other two hold the date in text
  15       format, and will hold years up to 9999.
  16
  17       The integer is
  18           "png_uint_16 year" in png_time_struct.
  19
  20       The strings are
  21           "png_charp time_buffer" in png_struct and
  22           "near_time_buffer", which is a local character string in png.c.
  23
  24       There are seven time-related functions:
  25
  26           png_convert_to_rfc_1123() in png.c
  27             (formerly png_convert_to_rfc_1152() in error)
  28           png_convert_from_struct_tm() in pngwrite.c, called in pngwrite.c
  29           png_convert_from_time_t() in pngwrite.c
  30           png_get_tIME() in pngget.c
  31           png_handle_tIME() in pngrutil.c, called in pngread.c
  32           png_set_tIME() in pngset.c
  33           png_write_tIME() in pngwutil.c, called in pngwrite.c
  34
  35       All appear to handle dates properly in a Y2K environment.  The
  36       png_convert_from_time_t() function calls gmtime() to convert from system
  37       clock time, which returns (year - 1900), which we properly convert to
  38       the full 4-digit year.  There is a possibility that applications using
  39       libpng are not passing 4-digit years into the png_convert_to_rfc_1123()
  40       function, or that they are incorrectly passing only a 2-digit year
  41       instead of "year - 1900" into the png_convert_from_struct_tm() function,
  42       but this is not under our control.  The libpng documentation has always
  43       stated that it works with 4-digit years, and the APIs have been
  44       documented as such.
  45
  46       The tIME chunk itself is also Y2K compliant.  It uses a 2-byte unsigned
  47       integer to hold the year, and can hold years as large as 65535.
  48
  49       zlib, upon which libpng depends, is also Y2K compliant.  It contains
  50       no date-related code.
  51
  52
  53          Glenn Randers-Pehrson
  54          libpng maintainer
  55          PNG Development Group