56 lines
2.3 KiB
Plaintext
56 lines
2.3 KiB
Plaintext
Y2K compliance in libpng:
|
|
=========================
|
|
|
|
June 8, 2011
|
|
|
|
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 1.2.45beta03 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
|