Y2K compliance in libpng:
=========================
-
- January 13, 1999
-
+
+ July 8, 2002
+
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 0.81 and
- upward are Y2K compliant. It is my belief that earlier versions were
- also Y2K compliant.
-
+
+ This is your unofficial assurance that libpng from version 0.71 and
+ upward through 1.2.4 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
+ 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_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
+
+ 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 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.
-
+ 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