lib/timespec.h

   1 /* timespec -- System time interface
   2
   3    Copyright (C) 2000, 2002, 2004-2005, 2007, 2009-2018 Free Software
   4    Foundation, Inc.
   5
   6    This program is free software: you can redistribute it and/or modify
   7    it under the terms of the GNU General Public License as published by
   8    the Free Software Foundation; either version 3 of the License, or
   9    (at your option) any later version.
  10
  11    This program is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14    GNU General Public License for more details.
  15
  16    You should have received a copy of the GNU General Public License
  17    along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
  18
  19 #if ! defined TIMESPEC_H
  20 # define TIMESPEC_H
  21
  22 # include <time.h>
  23
  24 #ifndef _GL_INLINE_HEADER_BEGIN
  25  #error "Please include config.h first."
  26 #endif
  27 _GL_INLINE_HEADER_BEGIN
  28 #ifndef _GL_TIMESPEC_INLINE
  29 # define _GL_TIMESPEC_INLINE _GL_INLINE
  30 #endif
  31
  32 #ifdef __cplusplus
  33 extern "C" {
  34 #endif
  35
  36 #include "verify.h"
  37
  38 /* Resolution of timespec timestamps (in units per second), and log
  39    base 10 of the resolution.  */
  40
  41 enum { TIMESPEC_RESOLUTION = 1000000000 };
  42 enum { LOG10_TIMESPEC_RESOLUTION = 9 };
  43
  44 /* Return a timespec with seconds S and nanoseconds NS.  */
  45
  46 _GL_TIMESPEC_INLINE struct timespec
  47 make_timespec (time_t s, long int ns)
  48 {
  49   struct timespec r;
  50   r.tv_sec = s;
  51   r.tv_nsec = ns;
  52   return r;
  53 }
  54
  55 /* Return negative, zero, positive if A < B, A == B, A > B, respectively.
  56
  57    For each timestamp T, this code assumes that either:
  58
  59      * T.tv_nsec is in the range 0..999999999; or
  60      * T.tv_sec corresponds to a valid leap second on a host that supports
  61        leap seconds, and T.tv_nsec is in the range 1000000000..1999999999; or
  62      * T.tv_sec is the minimum time_t value and T.tv_nsec is -1; or
  63        T.tv_sec is the maximum time_t value and T.tv_nsec is 2000000000.
  64        This allows for special struct timespec values that are less or
  65        greater than all possible valid timestamps.
  66
  67    In all these cases, it is safe to subtract two tv_nsec values and
  68    convert the result to integer without worrying about overflow on
  69    any platform of interest to the GNU project, since all such
  70    platforms have 32-bit int or wider.
  71
  72    Replacing "a.tv_nsec - b.tv_nsec" with something like
  73    "a.tv_nsec < b.tv_nsec ? -1 : a.tv_nsec > b.tv_nsec" would cause
  74    this function to work in some cases where the above assumption is
  75    violated, but not in all cases (e.g., a.tv_sec==1, a.tv_nsec==-2,
  76    b.tv_sec==0, b.tv_nsec==999999999) and is arguably not worth the
  77    extra instructions.  Using a subtraction has the advantage of
  78    detecting some invalid cases on platforms that detect integer
  79    overflow.  */
  80
  81 _GL_TIMESPEC_INLINE int _GL_ATTRIBUTE_PURE
  82 timespec_cmp (struct timespec a, struct timespec b)
  83 {
  84   if (a.tv_sec < b.tv_sec)
  85     return -1;
  86   if (a.tv_sec > b.tv_sec)
  87     return 1;
  88
  89   /* Pacify gcc -Wstrict-overflow (bleeding-edge circa 2017-10-02).  See:
  90      https://lists.gnu.org/r/bug-gnulib/2017-10/msg00006.html  */
  91   assume (-1 <= a.tv_nsec && a.tv_nsec <= 2 * TIMESPEC_RESOLUTION);
  92   assume (-1 <= b.tv_nsec && b.tv_nsec <= 2 * TIMESPEC_RESOLUTION);
  93
  94   return a.tv_nsec - b.tv_nsec;
  95 }
  96
  97 /* Return -1, 0, 1, depending on the sign of A.  A.tv_nsec must be
  98    nonnegative.  */
  99 _GL_TIMESPEC_INLINE int _GL_ATTRIBUTE_PURE
 100 timespec_sign (struct timespec a)
 101 {
 102   return a.tv_sec < 0 ? -1 : a.tv_sec || a.tv_nsec;
 103 }
 104
 105 struct timespec timespec_add (struct timespec, struct timespec)
 106   _GL_ATTRIBUTE_CONST;
 107 struct timespec timespec_sub (struct timespec, struct timespec)
 108   _GL_ATTRIBUTE_CONST;
 109 struct timespec dtotimespec (double)
 110   _GL_ATTRIBUTE_CONST;
 111
 112 /* Return an approximation to A, of type 'double'.  */
 113 _GL_TIMESPEC_INLINE double
 114 timespectod (struct timespec a)
 115 {
 116   return a.tv_sec + a.tv_nsec / 1e9;
 117 }
 118
 119 void gettime (struct timespec *);
 120 int settime (struct timespec const *);
 121
 122 #ifdef __cplusplus
 123 }
 124 #endif
 125
 126 _GL_INLINE_HEADER_END
 127
 128 #endif