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 _GL_INLINE_HEADER_BEGIN
  25 #ifndef _GL_TIMESPEC_INLINE
  26 # define _GL_TIMESPEC_INLINE _GL_INLINE
  27 #endif
  28
  29 /* Return negative, zero, positive if A < B, A == B, A > B, respectively.
  30
  31    For each time stamp T, this code assumes that either:
  32
  33      * T.tv_nsec is in the range 0..999999999; or
  34      * T.tv_sec corresponds to a valid leap second on a host that supports
  35        leap seconds, and T.tv_nsec is in the range 1000000000..1999999999; or
  36      * T.tv_sec is the minimum time_t value and T.tv_nsec is -1; or
  37        T.tv_sec is the maximum time_t value and T.tv_nsec is 2000000000.
  38        This allows for special struct timespec values that are less or
  39        greater than all possible valid time stamps.
  40
  41    In all these cases, it is safe to subtract two tv_nsec values and
  42    convert the result to integer without worrying about overflow on
  43    any platform of interest to the GNU project, since all such
  44    platforms have 32-bit int or wider.
  45
  46    Replacing "(int) (a.tv_nsec - b.tv_nsec)" with something like
  47    "a.tv_nsec < b.tv_nsec ? -1 : a.tv_nsec > b.tv_nsec" would cause
  48    this function to work in some cases where the above assumption is
  49    violated, but not in all cases (e.g., a.tv_sec==1, a.tv_nsec==-2,
  50    b.tv_sec==0, b.tv_nsec==999999999) and is arguably not worth the
  51    extra instructions.  Using a subtraction has the advantage of
  52    detecting some invalid cases on platforms that detect integer
  53    overflow.
  54
  55    The (int) cast avoids a gcc -Wconversion warning.  */
  56
  57 _GL_TIMESPEC_INLINE int
  58 timespec_cmp (struct timespec a, struct timespec b)
  59 {
  60   return (a.tv_sec < b.tv_sec ? -1
  61           : a.tv_sec > b.tv_sec ? 1
  62           : (int) (a.tv_nsec - b.tv_nsec));
  63 }
  64
  65 /* Return -1, 0, 1, depending on the sign of A.  A.tv_nsec must be
  66    nonnegative.  */
  67 _GL_TIMESPEC_INLINE int
  68 timespec_sign (struct timespec a)
  69 {
  70   return a.tv_sec < 0 ? -1 : a.tv_sec || a.tv_nsec;
  71 }
  72
  73 struct timespec timespec_add (struct timespec, struct timespec)
  74   _GL_ATTRIBUTE_CONST;
  75 struct timespec timespec_sub (struct timespec, struct timespec)
  76   _GL_ATTRIBUTE_CONST;
  77 struct timespec dtotimespec (double)
  78   _GL_ATTRIBUTE_CONST;
  79
  80 /* Return an approximation to A, of type 'double'.  */
  81 _GL_TIMESPEC_INLINE double
  82 timespectod (struct timespec a)
  83 {
  84   return a.tv_sec + a.tv_nsec / 1e9;
  85 }
  86
  87 void gettime (struct timespec *);
  88 int settime (struct timespec const *);
  89
  90 _GL_INLINE_HEADER_END
  91
  92 #endif