| 1 | Y2K compliance in libpng: |
| 2 | ========================= |
| 3 | |
| 4 | January 13, 1999 |
| 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 0.81 and |
| 10 | upward are Y2K compliant. It is my belief that earlier versions were |
| 11 | 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 incorrectly passing only a 2-digit year instead of |
| 41 | "year - 1900" into the png_convert_from_struct_tm() function, but this |
| 42 | is not under our control. The libpng documentation has always stated |
| 43 | that it works with 4-digit years, and the APIs have been documented as |
| 44 | 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 | |
| 50 | Glenn Randers-Pehrson |
| 51 | libpng maintainer |
| 52 | PNG Development Group |