diff options
Diffstat (limited to 'lib/getdate.y')
| -rw-r--r-- | lib/getdate.y | 23 |
1 files changed, 19 insertions, 4 deletions
diff --git a/lib/getdate.y b/lib/getdate.y index a4a445da0..2f72f045a 100644 --- a/lib/getdate.y +++ b/lib/getdate.y @@ -84,6 +84,21 @@ # define ATTRIBUTE_UNUSED __attribute__ ((__unused__)) #endif +/* Shift A right by B bits portably, by dividing A by 2**B and + truncating towards minus infinity. A and B should be free of side + effects, and B should be in the range 0 <= B <= INT_BITS - 2, where + INT_BITS is the number of useful bits in an int. GNU code can + assume that INT_BITS is at least 32. + + ISO C99 says that A >> B is implementation-defined if A < 0. Some + implementations (e.g., UNICOS 9.0 on a Cray Y-MP EL) don't shift + right in the usual way when A < 0, so SHR falls back on division if + ordinary A >> B doesn't seem to be the usual signed shift. */ +#define SHR(a, b) \ + (-1 >> 1 == -1 \ + ? (a) >> (b) \ + : (a) / (1 << (b)) - ((a) % (1 << (b)) < 0)) + #define EPOCH_YEAR 1970 #define TM_YEAR_BASE 1900 @@ -734,12 +749,12 @@ tm_diff (struct tm const *a, struct tm const *b) { /* Compute intervening leap days correctly even if year is negative. Take care to avoid int overflow in leap day calculations. */ - int a4 = (a->tm_year >> 2) + (TM_YEAR_BASE >> 2) - ! (a->tm_year & 3); - int b4 = (b->tm_year >> 2) + (TM_YEAR_BASE >> 2) - ! (b->tm_year & 3); + int a4 = SHR (a->tm_year, 2) + SHR (TM_YEAR_BASE, 2) - ! (a->tm_year & 3); + int b4 = SHR (b->tm_year, 2) + SHR (TM_YEAR_BASE, 2) - ! (b->tm_year & 3); int a100 = a4 / 25 - (a4 % 25 < 0); int b100 = b4 / 25 - (b4 % 25 < 0); - int a400 = a100 >> 2; - int b400 = b100 >> 2; + int a400 = SHR (a100, 2); + int b400 = SHR (b100, 2); int intervening_leap_days = (a4 - b4) - (a100 - b100) + (a400 - b400); long int ayear = a->tm_year; long int years = ayear - b->tm_year; |