libpng/Y2KINFO

56 lines
2.3 KiB
Plaintext
Raw Normal View History

1999-01-13 23:06:39 -05:00
Y2K compliance in libpng:
=========================
2000-02-05 00:40:16 -05:00
November 18, 2009
2000-02-05 00:40:16 -05:00
1999-01-13 23:06:39 -05:00
Since the PNG Development group is an ad-hoc body, we can't make
an official declaration.
2000-02-05 00:40:16 -05:00
1999-09-17 13:27:26 -04:00
This is your unofficial assurance that libpng from version 0.71 and
2009-11-14 08:36:54 -05:00
upward through 1.2.41rc01 are Y2K compliant. It is my belief that earlier
1999-09-17 13:27:26 -04:00
versions were also Y2K compliant.
2000-02-05 00:40:16 -05:00
1999-01-13 23:06:39 -05:00
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.
2000-02-05 00:40:16 -05:00
1999-01-13 23:06:39 -05:00
The integer is
"png_uint_16 year" in png_time_struct.
2000-02-05 00:40:16 -05:00
1999-01-13 23:06:39 -05:00
The strings are
"png_charp time_buffer" in png_struct and
"near_time_buffer", which is a local character string in png.c.
2000-02-05 00:40:16 -05:00
1999-01-13 23:06:39 -05:00
There are seven time-related functions:
2000-02-05 00:40:16 -05:00
png_convert_to_rfc_1123() in png.c
1999-01-13 23:06:39 -05:00
(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
2000-02-05 00:40:16 -05:00
All appear to handle dates properly in a Y2K environment. The
1999-01-13 23:06:39 -05:00
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()
1999-09-17 13:27:26 -04:00
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.
2000-02-05 00:40:16 -05:00
1999-01-13 23:06:39 -05:00
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.
1999-09-17 13:27:26 -04:00
zlib, upon which libpng depends, is also Y2K compliant. It contains
no date-related code.
2000-02-05 00:40:16 -05:00
1999-01-13 23:06:39 -05:00
Glenn Randers-Pehrson
libpng maintainer
PNG Development Group