diff options
Diffstat (limited to 'timezone/tzfile.h')
| -rw-r--r-- | timezone/tzfile.h | 17 |
1 files changed, 13 insertions, 4 deletions
diff --git a/timezone/tzfile.h b/timezone/tzfile.h index 0921c3c339..0e9966a950 100644 --- a/timezone/tzfile.h +++ b/timezone/tzfile.h @@ -21,7 +21,7 @@ #ifndef lint #ifndef NOID -static char tzfilehid[] = "@(#)tzfile.h 7.14"; +static char tzfilehid[] = "@(#)tzfile.h 7.16"; #endif /* !defined NOID */ #endif /* !defined lint */ @@ -156,12 +156,21 @@ struct tzhead { #define EPOCH_YEAR 1970 #define EPOCH_WDAY TM_THURSDAY +#define isleap(y) (((y) % 4) == 0 && (((y) % 100) != 0 || ((y) % 400) == 0)) + /* -** Accurate only for the past couple of centuries; -** that will probably do. +** Since everything in isleap is modulo 400 (or a factor of 400), we know that +** isleap(y) == isleap(y % 400) +** and so +** isleap(a + b) == isleap((a + b) % 400) +** or +** isleap(a + b) == isleap(a % 400 + b % 400) +** This is true even if % means modulo rather than Fortran remainder +** (which is allowed by C89 but not C99). +** We use this to avoid addition overflow problems. */ -#define isleap(y) (((y) % 4) == 0 && (((y) % 100) != 0 || ((y) % 400) == 0)) +#define isleap_sum(a, b) isleap((a) % 400 + (b) % 400) #ifndef USG |