| /* Copyright (C) 1991-2016 Free Software Foundation, Inc. |
| This file is part of the GNU C Library. |
| |
| The GNU C Library is free software; you can redistribute it and/or |
| modify it under the terms of the GNU Lesser General Public |
| License as published by the Free Software Foundation; either |
| version 2.1 of the License, or (at your option) any later version. |
| |
| The GNU C Library is distributed in the hope that it will be useful, |
| but WITHOUT ANY WARRANTY; without even the implied warranty of |
| MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
| Lesser General Public License for more details. |
| |
| You should have received a copy of the GNU Lesser General Public |
| License along with the GNU C Library; if not, see |
| <http://www.gnu.org/licenses/>. */ |
| |
| /* Written by Paul Eggert <eggert@cs.ucla.edu>. */ |
| |
| #include <time.h> |
| |
| #include <limits.h> |
| #include <float.h> |
| #include <stdint.h> |
| |
| #define TYPE_BITS(type) (sizeof (type) * CHAR_BIT) |
| #define TYPE_FLOATING(type) ((type) 0.5 == 0.5) |
| #define TYPE_SIGNED(type) ((type) -1 < 0) |
| |
| /* Return the difference between TIME1 and TIME0, where TIME0 <= TIME1. |
| time_t is known to be an integer type. */ |
| |
| static double |
| subtract (time_t time1, time_t time0) |
| { |
| if (! TYPE_SIGNED (time_t)) |
| return time1 - time0; |
| else |
| { |
| /* Optimize the common special cases where time_t |
| can be converted to uintmax_t without losing information. */ |
| uintmax_t dt = (uintmax_t) time1 - (uintmax_t) time0; |
| double delta = dt; |
| |
| if (UINTMAX_MAX / 2 < INTMAX_MAX) |
| { |
| /* This is a rare host where uintmax_t has padding bits, and possibly |
| information was lost when converting time_t to uintmax_t. |
| Check for overflow by comparing dt/2 to (time1/2 - time0/2). |
| Overflow occurred if they differ by more than a small slop. |
| Thanks to Clive D.W. Feather for detailed technical advice about |
| hosts with padding bits. |
| |
| In the following code the "h" prefix means half. By range |
| analysis, we have: |
| |
| -0.5 <= ht1 - 0.5*time1 <= 0.5 |
| -0.5 <= ht0 - 0.5*time0 <= 0.5 |
| -1.0 <= dht - 0.5*(time1 - time0) <= 1.0 |
| |
| If overflow has not occurred, we also have: |
| |
| -0.5 <= hdt - 0.5*(time1 - time0) <= 0 |
| -1.0 <= dht - hdt <= 1.5 |
| |
| and since dht - hdt is an integer, we also have: |
| |
| -1 <= dht - hdt <= 1 |
| |
| or equivalently: |
| |
| 0 <= dht - hdt + 1 <= 2 |
| |
| In the above analysis, all the operators have their exact |
| mathematical semantics, not C semantics. However, dht - hdt + |
| 1 is unsigned in C, so it need not be compared to zero. */ |
| |
| uintmax_t hdt = dt / 2; |
| time_t ht1 = time1 / 2; |
| time_t ht0 = time0 / 2; |
| time_t dht = ht1 - ht0; |
| |
| if (2 < dht - hdt + 1) |
| { |
| /* Repair delta overflow. |
| |
| The following expression contains a second rounding, |
| so the result may not be the closest to the true answer. |
| This problem occurs only with very large differences. |
| It's too painful to fix this portably. */ |
| |
| delta = dt + 2.0L * (UINTMAX_MAX - UINTMAX_MAX / 2); |
| } |
| } |
| |
| return delta; |
| } |
| } |
| |
| /* Return the difference between TIME1 and TIME0. */ |
| double |
| __difftime (time_t time1, time_t time0) |
| { |
| /* Convert to double and then subtract if no double-rounding error could |
| result. */ |
| |
| if (TYPE_BITS (time_t) <= DBL_MANT_DIG |
| || (TYPE_FLOATING (time_t) && sizeof (time_t) < sizeof (long double))) |
| return (double) time1 - (double) time0; |
| |
| /* Likewise for long double. */ |
| |
| if (TYPE_BITS (time_t) <= LDBL_MANT_DIG || TYPE_FLOATING (time_t)) |
| return (long double) time1 - (long double) time0; |
| |
| /* Subtract the smaller integer from the larger, convert the difference to |
| double, and then negate if needed. */ |
| |
| return time1 < time0 ? - subtract (time0, time1) : subtract (time1, time0); |
| } |
| strong_alias (__difftime, difftime) |