-/* Copyright (C) 1991, 1994, 1996 Free Software Foundation, Inc.
+/* Copyright (C) 1991-2019 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
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. */
+ License along with the GNU C Library; if not, see
+ <https://www.gnu.org/licenses/>. */
+
+/* Written by Paul Eggert <eggert@cs.ucla.edu>. */
#include <time.h>
-#include <values.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 (__time64_t time1, __time64_t time0)
+{
+ if (! TYPE_SIGNED (__time64_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;
+ __time64_t ht1 = time1 / 2;
+ __time64_t ht0 = time0 / 2;
+ __time64_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 (time1, time0)
- time_t time1;
- time_t time0;
+__difftime64 (__time64_t time1, __time64_t time0)
{
- /* Algorithm courtesy Paul Eggert (eggert@twinsun.com). */
-
- time_t delta, hibit;
+ /* Convert to double and then subtract if no double-rounding error could
+ result. */
- if (sizeof (time_t) < sizeof (double))
+ if (TYPE_BITS (__time64_t) <= DBL_MANT_DIG
+ || (TYPE_FLOATING (__time64_t) && sizeof (__time64_t) < sizeof (long double)))
return (double) time1 - (double) time0;
- if (sizeof (time_t) < sizeof (long double))
+
+ /* Likewise for long double. */
+
+ if (TYPE_BITS (__time64_t) <= LDBL_MANT_DIG || TYPE_FLOATING (__time64_t))
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;
+ /* 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);
}
+
+/* Provide a 32-bit wrapper if needed. */
+
+#if __TIMESIZE != 64
+
+libc_hidden_def (__difftime64)
+
+double
+__difftime (time_t time1, time_t time0)
+{
+ return __difftime64 (time1, time0);
+}
+
+#endif
+
+strong_alias (__difftime, difftime)
projects / thirdparty / glibc.git / blobdiff