compat/mkgmtime.c

   1 /* mkgmtime.c - make time corresponding to a GMT timeval struct
   2  * $Id: mkgmtime.c,v 1.10 2003/10/22 18:50:12 rjs3 Exp $
   3  *
   4  * Copyright (c) 1998-2003 Carnegie Mellon University.  All rights reserved.
   5  *
   6  * Redistribution and use in source and binary forms, with or without
   7  * modification, are permitted provided that the following conditions
   8  * are met:
   9  *
  10  * 1. Redistributions of source code must retain the above copyright
  11  *    notice, this list of conditions and the following disclaimer.
  12  *
  13  * 2. Redistributions in binary form must reproduce the above copyright
  14  *    notice, this list of conditions and the following disclaimer in
  15  *    the documentation and/or other materials provided with the
  16  *    distribution.
  17  *
  18  * 3. The name "Carnegie Mellon University" must not be used to
  19  *    endorse or promote products derived from this software without
  20  *    prior written permission. For permission or any other legal
  21  *    details, please contact
  22  *      Office of Technology Transfer
  23  *      Carnegie Mellon University
  24  *      5000 Forbes Avenue
  25  *      Pittsburgh, PA  15213-3890
  26  *      (412) 268-4387, fax: (412) 268-7395
  27  *      tech-transfer@andrew.cmu.edu
  28  *
  29  * 4. Redistributions of any form whatsoever must retain the following
  30  *    acknowledgment:
  31  *    "This product includes software developed by Computing Services
  32  *     at Carnegie Mellon University (http://www.cmu.edu/computing/)."
  33  *
  34  * CARNEGIE MELLON UNIVERSITY DISCLAIMS ALL WARRANTIES WITH REGARD TO
  35  * THIS SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
  36  * AND FITNESS, IN NO EVENT SHALL CARNEGIE MELLON UNIVERSITY BE LIABLE
  37  * FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
  38  * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN
  39  * AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING
  40  * OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  41  */
  42
  43 /*
  44  * Copyright (c) 1987, 1989, 1993
  45  *      The Regents of the University of California.  All rights reserved.
  46  *
  47  * This code is derived from software contributed to Berkeley by
  48  * Arthur David Olson of the National Cancer Institute.
  49  *
  50  * Redistribution and use in source and binary forms, with or without
  51  * modification, are permitted provided that the following conditions
  52  * are met:
  53  * 1. Redistributions of source code must retain the above copyright
  54  *    notice, this list of conditions and the following disclaimer.
  55  * 2. Redistributions in binary form must reproduce the above copyright
  56  *    notice, this list of conditions and the following disclaimer in the
  57  *    documentation and/or other materials provided with the distribution.
  58  * 3. All advertising materials mentioning features or use of this software
  59  *    must display the following acknowledgement:
  60  *      This product includes software developed by the University of
  61  *      California, Berkeley and its contributors.
  62  * 4. Neither the name of the University nor the names of its contributors
  63  *    may be used to endorse or promote products derived from this software
  64  *    without specific prior written permission.
  65  *
  66  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  67  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  68  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  69  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  70  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  71  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  72  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  73  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  74  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  75  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  76  * SUCH DAMAGE.
  77  */
  78
  79 /*
  80  * Adapted from code provided by Robert Elz, who writes:
  81  *      The "best" way to do mktime I think is based on an idea of Bob
  82  *      Kridle's (so its said...) from a long time ago. (mtxinu!kridle now).
  83  *      It does a binary search of the time_t space.  Since time_t's are
  84  *      just 32 bits, its a max of 32 iterations (even at 64 bits it
  85  *      would still be very reasonable).
  86  */
  87
  88 #include "mkgmtime.h"
  89
  90 #ifndef WRONG
  91 #define WRONG (-1)
  92 #endif /* !defined WRONG */
  93
  94 static int tmcomp(const struct tm *const atmp, const struct tm *const btmp)
  95 {
  96         register int result;
  97
  98         if ((result = (atmp->tm_year - btmp->tm_year)) == 0 &&
  99             (result = (atmp->tm_mon - btmp->tm_mon)) == 0 &&
 100             (result = (atmp->tm_mday - btmp->tm_mday)) == 0 &&
 101             (result = (atmp->tm_hour - btmp->tm_hour)) == 0 &&
 102             (result = (atmp->tm_min - btmp->tm_min)) == 0)
 103                 result = atmp->tm_sec - btmp->tm_sec;
 104         return result;
 105 }
 106
 107 time_t mkgmtime(struct tm *const tmp)
 108 {
 109         register int dir;
 110         register int bits;
 111         register int saved_seconds;
 112         time_t t;
 113         struct tm yourtm, *mytm;
 114
 115         yourtm = *tmp;
 116         saved_seconds = yourtm.tm_sec;
 117         yourtm.tm_sec = 0;
 118         /*
 119          * Calculate the number of magnitude bits in a time_t
 120          * (this works regardless of whether time_t is
 121          * signed or unsigned, though lint complains if unsigned).
 122          */
 123         for (bits = 0, t = 1; t > 0; ++bits, t <<= 1)
 124                 ;
 125         /*
 126          * If time_t is signed, then 0 is the median value,
 127          * if time_t is unsigned, then 1 << bits is median.
 128          */
 129         t = (t < 0) ? 0 : ((time_t) 1 << bits);
 130
 131         /* Some gmtime() implementations are broken and will return
 132          * NULL for time_ts larger than 40 bits even on 64-bit platforms
 133          * so we'll just cap it at 40 bits
 134          */
 135         if(bits > 40) bits = 40;
 136
 137         for ( ; ; ) {
 138                 mytm = gmtime(&t);
 139
 140                 if(!mytm) return WRONG;
 141
 142                 dir = tmcomp(mytm, &yourtm);
 143                 if (dir != 0) {
 144                         if (bits-- < 0)
 145                                 return WRONG;
 146                         if (bits < 0)
 147                                 --t;
 148                         else if (dir > 0)
 149                                 t -= (time_t) 1 << bits;
 150                         else
 151                                 t += (time_t) 1 << bits;
 152                         continue;
 153                 }
 154                 break;
 155         }
 156         t += saved_seconds;
 157         return t;
 158 }