Strftime's %C and %y formats versus wide-ranging tm_year valu es
eggert at CS.UCLA.EDU
Tue Oct 5 20:30:22 UTC 2004
"Olson, Arthur David (NIH/NCI)" <olsona at dc37a.nci.nih.gov> writes:
> + #define C99IPMOD(a, b) ((-1 % 2 < 0 || (a) >= 0) ? \
> + ((a) % (b)) : ((a) % (b) - (b)))
A quick reaction: this returns the wrong answer if -1%2 is 1 and a%b
is zero. But see below.
> + #define isleap_sum(a, b) isleap(C99IPMOD((a), 400) + C99IPMOD((b), 400))
Surely this is overkill. You can simply use this:
#define isleap_sum(a, b) isleap((a) % 400 + (b) % 400)
as this will work regardless of whether % means Fortran remainder or
> ! year = (double) timeptr->tm_year + (double) TM_YEAR_BASE;
This sort of trick won't work in general on hosts that have 64-bit int
and 64-bit double (e.g., some Crays), due to rounding problems.
> + i = a + b;
> + if ((i > a) == (b > 0))
This kind of overflow-checking won't work reliably in general, since
the behavior is undefined if signed integer overflow occurs. I have
run into compilers where the above code won't detect overflow
I have a draft solution for the above problems but would like to think
about it for a day or so before posting.
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