1 Y2K compliance in libpng: 2 ========================= 3 4 July 9, 2011 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 1.2.46 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 56
