From e547d07a488ab17397217e2a57594c78bf747373 Mon Sep 17 00:00:00 2001 From: Eric Andersen Date: Sat, 4 Nov 2000 04:37:24 +0000 Subject: More cleanups. Fix things so tinylogin compiles. Fix a bug in getdelim -- patch from David Whedon . --- libc/misc/time/difftime.c | 67 +++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 67 insertions(+) create mode 100644 libc/misc/time/difftime.c (limited to 'libc/misc/time/difftime.c') diff --git a/libc/misc/time/difftime.c b/libc/misc/time/difftime.c new file mode 100644 index 000000000..6a9b708ea --- /dev/null +++ b/libc/misc/time/difftime.c @@ -0,0 +1,67 @@ +/* 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 Library General Public License as + published by the Free Software Foundation; either version 2 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 + Library General Public License for more details. + + You should have received a copy of the GNU Library General Public + License along with the GNU C Library; see the file COPYING.LIB. If not, + write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330, + Boston, MA 02111-1307, USA. */ + +#include +#include +#include + + +/* 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) << ((sizeof (time_t) * CHAR_BIT) - 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; +} -- cgit v1.2.3