Re: PPSkit-0.9.0 has a Y2K problem

[Harald Koenig]

On Jan 05, Ulrich Windl wrote:

> In PPSkit-0.9.0 I added a routine from fs/fat/misc.c to convert a UNIX date to 
> broken time (YYYY MO DD HH MI SS). As it turned out the routine produced a 
> 1999-12-32 on January 1st, and since then there's one day missing. Maybe I did 
> something stupied, maybe the problem is also in the original routine. Anyway 
> here is a test suite to see yourself:

this problem doesn't only show up for Y2K but before _any_ lap year!
and here is a fix for this off-by-one bug:

@@ -66,10 +67,10 @@
        year = day / 365;               /* non-leap years since epoch */
        printf("[d=%d y=%d] ", day, year);
        /* correct for leap years in epoch: 1972 (2) was the first */
-       if ((year + 2) / 4 + 365 * year > day)
+       if ((year + 1) / 4 + 365 * year > day)
                year--;
        /* reduce to day in current year */
-       day -= (year + 2) / 4 + 365 * year;
+       day -= (year + 1) / 4 + 365 * year;
        printf("[d=%d y=%d] ", day, year);
        /* map March, 1st to Feburary, 29nd for leap years */
        if (day == 59 && ((year + 2) & 3) == 0) {

the code in 2.2.x kernel sources (fat_date_unix2dos() in fs/fat/misc.c)
looks ok though:

        year = day/365;
        if ((year+3)/4+365*year > day) year--;
        day -= (year+3)/4+365*year;

because here `year' is based on 1980 (epoch for MSDOS) and not 1970,
which gives that offset of 2 (== 10 % 4).

Harald
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