lib/timespec.h

   1 /* timespec -- System time interface
   2
   3    Copyright (C) 2000, 2002, 2004-2005, 2007, 2009-2017 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 <http://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 /* Resolution of timespec timestamps (in units per second), and log
  37    base 10 of the resolution.  */
  38
  39 enum { TIMESPEC_RESOLUTION = 1000000000 };
  40 enum { LOG10_TIMESPEC_RESOLUTION = 9 };
  41
  42 /* Return a timespec with seconds S and nanoseconds NS.  */
  43
  44 _GL_TIMESPEC_INLINE struct timespec
  45 make_timespec (time_t s, long int ns)
  46 {
  47   struct timespec r;
  48   r.tv_sec = s;
  49   r.tv_nsec = ns;
  50   return r;
  51 }
  52
  53 /* Return negative, zero, positive if A < B, A == B, A > B, respectively.
  54
  55    For each timestamp T, this code assumes that either:
  56
  57      * T.tv_nsec is in the range 0..999999999; or
  58      * T.tv_sec corresponds to a valid leap second on a host that supports
  59        leap seconds, and T.tv_nsec is in the range 1000000000..1999999999; or
  60      * T.tv_sec is the minimum time_t value and T.tv_nsec is -1; or
  61        T.tv_sec is the maximum time_t value and T.tv_nsec is 2000000000.
  62        This allows for special struct timespec values that are less or
  63        greater than all possible valid timestamps.
  64
  65    In all these cases, it is safe to subtract two tv_nsec values and
  66    convert the result to integer without worrying about overflow on
  67    any platform of interest to the GNU project, since all such
  68    platforms have 32-bit int or wider.
  69
  70    Replacing "(int) (a.tv_nsec - b.tv_nsec)" with something like
  71    "a.tv_nsec < b.tv_nsec ? -1 : a.tv_nsec > b.tv_nsec" would cause
  72    this function to work in some cases where the above assumption is
  73    violated, but not in all cases (e.g., a.tv_sec==1, a.tv_nsec==-2,
  74    b.tv_sec==0, b.tv_nsec==999999999) and is arguably not worth the
  75    extra instructions.  Using a subtraction has the advantage of
  76    detecting some invalid cases on platforms that detect integer
  77    overflow.
  78
  79    The (int) cast avoids a gcc -Wconversion warning.  */
  80
  81 _GL_TIMESPEC_INLINE int _GL_ATTRIBUTE_PURE
  82 timespec_cmp (struct timespec a, struct timespec b)
  83 {
  84   return (a.tv_sec < b.tv_sec ? -1
  85           : a.tv_sec > b.tv_sec ? 1
  86           : (int) (a.tv_nsec - b.tv_nsec));
  87 }
  88
  89 /* Return -1, 0, 1, depending on the sign of A.  A.tv_nsec must be
  90    nonnegative.  */
  91 _GL_TIMESPEC_INLINE int _GL_ATTRIBUTE_PURE
  92 timespec_sign (struct timespec a)
  93 {
  94   return a.tv_sec < 0 ? -1 : a.tv_sec || a.tv_nsec;
  95 }
  96
  97 struct timespec timespec_add (struct timespec, struct timespec)
  98   _GL_ATTRIBUTE_CONST;
  99 struct timespec timespec_sub (struct timespec, struct timespec)
 100   _GL_ATTRIBUTE_CONST;
 101 struct timespec dtotimespec (double)
 102   _GL_ATTRIBUTE_CONST;
 103
 104 /* Return an approximation to A, of type 'double'.  */
 105 _GL_TIMESPEC_INLINE double
 106 timespectod (struct timespec a)
 107 {
 108   return a.tv_sec + a.tv_nsec / 1e9;
 109 }
 110
 111 void gettime (struct timespec *);
 112 int settime (struct timespec const *);
 113
 114 #ifdef __cplusplus
 115 }
 116 #endif
 117
 118 _GL_INLINE_HEADER_END
 119
 120 #endif