Mercurial > fife-parpg
comparison ext/libpng-1.2.29/Y2KINFO @ 0:4a0efb7baf70
* Datasets becomes the new trunk and retires after that :-)
| author | mvbarracuda@33b003aa-7bff-0310-803a-e67f0ece8222 |
|---|---|
| date | Sun, 29 Jun 2008 18:44:17 +0000 |
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| -1:000000000000 | 0:4a0efb7baf70 |
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| 1 Y2K compliance in libpng: | |
| 2 ========================= | |
| 3 | |
| 4 May 8, 2008 | |
| 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 1.2.29 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 |