lib/timespec.h

   1 /* timespec -- System time interface
   2
   3    Copyright (C) 2000, 2002, 2004-2005, 2007, 2009-2013 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 /* Resolution of timespec time stamps (in units per second), and log
  33    base 10 of the resolution.  */
  34
  35 enum { TIMESPEC_RESOLUTION = 1000000000 };
  36 enum { LOG10_TIMESPEC_RESOLUTION = 9 };
  37
  38 /* Return a timespec with seconds S and nanoseconds NS.  */
  39
  40 _GL_TIMESPEC_INLINE struct timespec
  41 make_timespec (time_t s, long int ns)
  42 {
  43   struct timespec r;
  44   r.tv_sec = s;
  45   r.tv_nsec = ns;
  46   return r;
  47 }
  48
  49 /* Return negative, zero, positive if A < B, A == B, A > B, respectively.
  50
  51    For each time stamp T, this code assumes that either:
  52
  53      * T.tv_nsec is in the range 0..999999999; or
  54      * T.tv_sec corresponds to a valid leap second on a host that supports
  55        leap seconds, and T.tv_nsec is in the range 1000000000..1999999999; or
  56      * T.tv_sec is the minimum time_t value and T.tv_nsec is -1; or
  57        T.tv_sec is the maximum time_t value and T.tv_nsec is 2000000000.
  58        This allows for special struct timespec values that are less or
  59        greater than all possible valid time stamps.
  60
  61    In all these cases, it is safe to subtract two tv_nsec values and
  62    convert the result to integer without worrying about overflow on
  63    any platform of interest to the GNU project, since all such
  64    platforms have 32-bit int or wider.
  65
  66    Replacing "(int) (a.tv_nsec - b.tv_nsec)" with something like
  67    "a.tv_nsec < b.tv_nsec ? -1 : a.tv_nsec > b.tv_nsec" would cause
  68    this function to work in some cases where the above assumption is
  69    violated, but not in all cases (e.g., a.tv_sec==1, a.tv_nsec==-2,
  70    b.tv_sec==0, b.tv_nsec==999999999) and is arguably not worth the
  71    extra instructions.  Using a subtraction has the advantage of
  72    detecting some invalid cases on platforms that detect integer
  73    overflow.
  74
  75    The (int) cast avoids a gcc -Wconversion warning.  */
  76
  77 _GL_TIMESPEC_INLINE int
  78 timespec_cmp (struct timespec a, struct timespec b)
  79 {
  80   return (a.tv_sec < b.tv_sec ? -1
  81           : a.tv_sec > b.tv_sec ? 1
  82           : (int) (a.tv_nsec - b.tv_nsec));
  83 }
  84
  85 /* Return -1, 0, 1, depending on the sign of A.  A.tv_nsec must be
  86    nonnegative.  */
  87 _GL_TIMESPEC_INLINE int
  88 timespec_sign (struct timespec a)
  89 {
  90   return a.tv_sec < 0 ? -1 : a.tv_sec || a.tv_nsec;
  91 }
  92
  93 struct timespec timespec_add (struct timespec, struct timespec)
  94   _GL_ATTRIBUTE_CONST;
  95 struct timespec timespec_sub (struct timespec, struct timespec)
  96   _GL_ATTRIBUTE_CONST;
  97 struct timespec dtotimespec (double)
  98   _GL_ATTRIBUTE_CONST;
  99
 100 /* Return an approximation to A, of type 'double'.  */
 101 _GL_TIMESPEC_INLINE double
 102 timespectod (struct timespec a)
 103 {
 104   return a.tv_sec + a.tv_nsec / 1e9;
 105 }
 106
 107 void gettime (struct timespec *);
 108 int settime (struct timespec const *);
 109
 110 _GL_INLINE_HEADER_END
 111
 112 #endif