diff options
Diffstat (limited to 'src/timezone/difftime.c')
| -rw-r--r-- | src/timezone/difftime.c | 168 |
1 files changed, 84 insertions, 84 deletions
diff --git a/src/timezone/difftime.c b/src/timezone/difftime.c index 636640d6f57..57b88deafee 100644 --- a/src/timezone/difftime.c +++ b/src/timezone/difftime.c @@ -1,84 +1,84 @@ -#include "pgtz.h"
-/*
-** This file is in the public domain, so clarified as of
-** June 5, 1996 by Arthur David Olson (arthur_david_olson@nih.gov).
-*/
-
-#ifndef lint
-#ifndef NOID
-static char elsieid[] = "@(#)difftime.c 7.9";
-#endif /* !defined NOID */
-#endif /* !defined lint */
-
-/*LINTLIBRARY*/
-
-#include "private.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;
-
- {
- time_t tt;
- double d;
- long_double ld;
-
- if (sizeof tt < sizeof d)
- return (double) time1 - (double) time0;
- if (sizeof tt < sizeof ld)
- 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;
-}
+#include "pgtz.h" +/* +** This file is in the public domain, so clarified as of +** June 5, 1996 by Arthur David Olson (arthur_david_olson@nih.gov). +*/ + +#ifndef lint +#ifndef NOID +static char elsieid[] = "@(#)difftime.c 7.9"; +#endif /* !defined NOID */ +#endif /* !defined lint */ + +/*LINTLIBRARY*/ + +#include "private.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; + + { + time_t tt; + double d; + long_double ld; + + if (sizeof tt < sizeof d) + return (double) time1 - (double) time0; + if (sizeof tt < sizeof ld) + 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; +} |