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0272a10d VZ |
1 | Y2K compliance in libpng: |
2 | ========================= | |
3 | ||
4 | September 8, 2007 | |
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 1.2.20 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 |