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Diffstat (limited to 'REORG.TODO/time/difftime.c')
| -rw-r--r-- | REORG.TODO/time/difftime.c | 121 |
1 files changed, 121 insertions, 0 deletions
diff --git a/REORG.TODO/time/difftime.c b/REORG.TODO/time/difftime.c new file mode 100644 index 0000000000..e5e3311744 --- /dev/null +++ b/REORG.TODO/time/difftime.c @@ -0,0 +1,121 @@ +/* Copyright (C) 1991-2017 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) |