mirror of
git://sourceware.org/git/glibc.git
synced 2024-12-09 04:11:27 +08:00
41bdb6e20c
2001-07-06 Paul Eggert <eggert@twinsun.com> * manual/argp.texi: Remove ignored LGPL copyright notice; it's not appropriate for documentation anyway. * manual/libc-texinfo.sh: "Library General Public License" -> "Lesser General Public License". 2001-07-06 Andreas Jaeger <aj@suse.de> * All files under GPL/LGPL version 2: Place under LGPL version 2.1.
67 lines
2.7 KiB
C
67 lines
2.7 KiB
C
/* Copyright (C) 1991, 1994, 1996 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, write to the Free
|
|
Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
|
|
02111-1307 USA. */
|
|
|
|
#include <time.h>
|
|
#include <values.h>
|
|
|
|
|
|
/* Return the difference between TIME1 and TIME0. */
|
|
double
|
|
difftime (time1, time0)
|
|
time_t time1;
|
|
time_t time0;
|
|
{
|
|
/* Algorithm courtesy Paul Eggert (eggert@twinsun.com). */
|
|
|
|
time_t delta, hibit;
|
|
|
|
if (sizeof (time_t) < sizeof (double))
|
|
return (double) time1 - (double) time0;
|
|
if (sizeof (time_t) < sizeof (long double))
|
|
return (long double) time1 - (long double) time0;
|
|
|
|
if (time1 < time0)
|
|
return - difftime (time0, time1);
|
|
|
|
/* As much as possible, avoid loss of precision by computing the
|
|
difference before converting to double. */
|
|
delta = time1 - time0;
|
|
if (delta >= 0)
|
|
return delta;
|
|
|
|
/* Repair delta overflow. */
|
|
hibit = (~ (time_t) 0) << (_TYPEBITS (time_t) - 1);
|
|
|
|
/* The following expression rounds twice, which means the result may not
|
|
be the closest to the true answer. For example, suppose time_t is
|
|
64-bit signed int, long_double is IEEE 754 double with default
|
|
rounding, time1 = 9223372036854775807 and time0 = -1536. Then the
|
|
true difference is 9223372036854777343, which rounds to
|
|
9223372036854777856 with a total error of 513. But delta overflows to
|
|
-9223372036854774273, which rounds to -9223372036854774784, and
|
|
correcting this by subtracting 2 * (long_double) hibit (i.e. by adding
|
|
2**64 = 18446744073709551616) yields 9223372036854776832, which rounds
|
|
to 9223372036854775808 with a total error of 1535 instead. This
|
|
problem occurs only with very large differences. It's too painful to
|
|
fix this portably. We are not alone in this problem; many C compilers
|
|
round twice when converting large unsigned types to small floating
|
|
types, so if time_t is unsigned the "return delta" above has the same
|
|
double-rounding problem. */
|
|
return delta - 2 * (long double) hibit;
|
|
}
|