freebsd-dev/lib/libc/stdtime/difftime.c
Daniel Eischen d201fe46e3 Remove _THREAD_SAFE and make libc thread-safe by default by
adding (weak definitions to) stubs for some of the pthread
functions.  If the threads library is linked in, the real
pthread functions will pulled in.

Use the following convention for system calls wrapped by the
threads library:
	__sys_foo - actual system call
	_foo - weak definition to __sys_foo
	foo - weak definition to __sys_foo

Change all libc uses of system calls wrapped by the threads
library from foo to _foo.  In order to define the prototypes
for _foo(), we introduce namespace.h and un-namespace.h
(suggested by bde).  All files that need to reference these
system calls, should include namespace.h before any standard
includes, then include un-namespace.h after the standard
includes and before any local includes.  <db.h> is an exception
and shouldn't be included in between namespace.h and
un-namespace.h  namespace.h will define foo to _foo, and
un-namespace.h will undefine foo.

Try to eliminate some of the recursive calls to MT-safe
functions in libc/stdio in preparation for adding a mutex
to FILE.  We have recursive mutexes, but would like to avoid
using them if possible.

Remove uneeded includes of <errno.h> from a few files.

Add $FreeBSD$ to a few files in order to pass commitprep.

Approved by:	-arch
2001-01-24 13:01:12 +00:00

82 lines
2.3 KiB
C

/*
** This file is in the public domain, so clarified as of
** June 5, 1996 by Arthur David Olson (arthur_david_olson@nih.gov).
*
* $FreeBSD$
*/
#ifndef lint
#ifndef NOID
static char elsieid[] = "@(#)difftime.c 7.7";
#endif /* !defined NOID */
#endif /* !defined lint */
/*LINTLIBRARY*/
#include "namespace.h"
#include "private.h"
#include "un-namespace.h"
/*
** Algorithm courtesy Paul Eggert (eggert@twinsun.com).
*/
#ifdef HAVE_LONG_DOUBLE
#define long_double long double
#endif /* defined HAVE_LONG_DOUBLE */
#ifndef HAVE_LONG_DOUBLE
#define long_double double
#endif /* !defined HAVE_LONG_DOUBLE */
double
difftime(time1, time0)
const time_t time1;
const time_t time0;
{
time_t delta;
time_t 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) << (TYPE_BIT(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;
** some 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 with those compilers.
*/
return delta - 2 * (long_double) hibit;
}