| /* |
| ** This file is in the public domain, so clarified as of |
| ** 1996-06-05 by Arthur David Olson. |
| */ |
| |
| /*LINTLIBRARY*/ |
| |
| #include "private.h" /* for time_t and TYPE_SIGNED */ |
| |
| /* Return -X as a double. Using this avoids casting to 'double'. */ |
| static double |
| dminus(double x) |
| { |
| return -x; |
| } |
| |
| double ATTRIBUTE_CONST |
| difftime(time_t time1, time_t time0) |
| { |
| /* |
| ** If double is large enough, simply convert and subtract |
| ** (assuming that the larger type has more precision). |
| */ |
| if (sizeof (time_t) < sizeof (double)) { |
| double t1 = time1, t0 = time0; |
| return t1 - t0; |
| } |
| |
| /* |
| ** The difference of two unsigned values can't overflow |
| ** if the minuend is greater than or equal to the subtrahend. |
| */ |
| if (!TYPE_SIGNED(time_t)) |
| return time0 <= time1 ? time1 - time0 : dminus(time0 - time1); |
| |
| /* Use uintmax_t if wide enough. */ |
| if (sizeof (time_t) <= sizeof (uintmax_t)) { |
| uintmax_t t1 = time1, t0 = time0; |
| return time0 <= time1 ? t1 - t0 : dminus(t0 - t1); |
| } |
| |
| /* |
| ** Handle cases where both time1 and time0 have the same sign |
| ** (meaning that their difference cannot overflow). |
| */ |
| if ((time1 < 0) == (time0 < 0)) |
| return time1 - time0; |
| |
| /* |
| ** The values have opposite signs and uintmax_t is too narrow. |
| ** This suffers from double rounding; attempt to lessen that |
| ** by using long double temporaries. |
| */ |
| { |
| long double t1 = time1, t0 = time0; |
| return t1 - t0; |
| } |
| } |