lib/timespec.h

   1 /* timespec -- System time interface
   2
   3    Copyright (C) 2000, 2002, 2004-2005, 2007, 2009-2012 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 /* Return negative, zero, positive if A < B, A == B, A > B, respectively.
  25
  26    For each time stamp T, this code assumes that either:
  27
  28      * T.tv_nsec is in the range 0..999999999; or
  29      * T.tv_sec corresponds to a valid leap second on a host that supports
  30        leap seconds, and T.tv_nsec is in the range 1000000000..1999999999; or
  31      * T.tv_sec is the minimum time_t value and T.tv_nsec is -1; or
  32        T.tv_sec is the maximum time_t value and T.tv_nsec is 2000000000.
  33        This allows for special struct timespec values that are less or
  34        greater than all possible valid time stamps.
  35
  36    In all these cases, it is safe to subtract two tv_nsec values and
  37    convert the result to integer without worrying about overflow on
  38    any platform of interest to the GNU project, since all such
  39    platforms have 32-bit int or wider.
  40
  41    Replacing "(int) (a.tv_nsec - b.tv_nsec)" with something like
  42    "a.tv_nsec < b.tv_nsec ? -1 : a.tv_nsec > b.tv_nsec" would cause
  43    this function to work in some cases where the above assumption is
  44    violated, but not in all cases (e.g., a.tv_sec==1, a.tv_nsec==-2,
  45    b.tv_sec==0, b.tv_nsec==999999999) and is arguably not worth the
  46    extra instructions.  Using a subtraction has the advantage of
  47    detecting some invalid cases on platforms that detect integer
  48    overflow.
  49
  50    The (int) cast avoids a gcc -Wconversion warning.  */
  51
  52 static inline int
  53 timespec_cmp (struct timespec a, struct timespec b)
  54 {
  55   return (a.tv_sec < b.tv_sec ? -1
  56           : a.tv_sec > b.tv_sec ? 1
  57           : (int) (a.tv_nsec - b.tv_nsec));
  58 }
  59
  60 /* Return -1, 0, 1, depending on the sign of A.  A.tv_nsec must be
  61    nonnegative.  */
  62 static inline int
  63 timespec_sign (struct timespec a)
  64 {
  65   return a.tv_sec < 0 ? -1 : a.tv_sec || a.tv_nsec;
  66 }
  67
  68 struct timespec timespec_add (struct timespec, struct timespec)
  69   _GL_ATTRIBUTE_CONST;
  70 struct timespec timespec_sub (struct timespec, struct timespec)
  71   _GL_ATTRIBUTE_CONST;
  72 struct timespec dtotimespec (double)
  73   _GL_ATTRIBUTE_CONST;
  74
  75 /* Return an approximation to A, of type 'double'.  */
  76 static inline double
  77 timespectod (struct timespec a)
  78 {
  79   return a.tv_sec + a.tv_nsec / 1e9;
  80 }
  81
  82 void gettime (struct timespec *);
  83 int settime (struct timespec const *);
  84
  85 #endif