X-Git-Url: http://erislabs.net/gitweb/?a=blobdiff_plain;f=lib%2Ftimespec.h;h=74d5749df60e075bdbec4576691259b6e69372c2;hb=7ef852ba849ac1fc4bef6d48e47e2dd3c0914feb;hp=cce2d663ad21ba73d15c81c6bdfa43d3a3eba704;hpb=3ac9552429c5a500717e1d3d129c32f7d0ea37a3;p=gnulib.git

diff --git a/lib/timespec.h b/lib/timespec.h
index cce2d663a..74d5749df 100644
--- a/lib/timespec.h
+++ b/lib/timespec.h
@@ -1,11 +1,12 @@
 /* timespec -- System time interface
 
-   Copyright (C) 2000, 2002, 2004, 2005, 2007 Free Software Foundation, Inc.
+   Copyright (C) 2000, 2002, 2004-2005, 2007, 2009-2011 Free Software
+   Foundation, Inc.
 
-   This program is free software; you can redistribute it and/or modify
+   This program is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
-   the Free Software Foundation; either version 2, or (at your option)
-   any later version.
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
 
    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ -13,8 +14,7 @@
    GNU General Public License for more details.
 
    You should have received a copy of the GNU General Public License
-   along with this program; if not, write to the Free Software Foundation,
-   Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
 
 #if ! defined TIMESPEC_H
 # define TIMESPEC_H
@@ -22,13 +22,39 @@
 # include <time.h>
 
 /* Return negative, zero, positive if A < B, A == B, A > B, respectively.
-   Assume the nanosecond components are in range, or close to it.  */
+
+   For each time stamp T, this code assumes that either:
+
+     * T.tv_nsec is in the range 0..999999999; or
+     * T.tv_sec corresponds to a valid leap second on a host that supports
+       leap seconds, and T.tv_nsec is in the range 1000000000..1999999999; or
+     * T.tv_sec is the minimum time_t value and T.tv_nsec is -1; or
+       T.tv_sec is the maximum time_t value and T.tv_nsec is 2000000000.
+       This allows for special struct timespec values that are less or
+       greater than all possible valid time stamps.
+
+   In all these cases, it is safe to subtract two tv_nsec values and
+   convert the result to integer without worrying about overflow on
+   any platform of interest to the GNU project, since all such
+   platforms have 32-bit int or wider.
+
+   Replacing "(int) (a.tv_nsec - b.tv_nsec)" with something like
+   "a.tv_nsec < b.tv_nsec ? -1 : a.tv_nsec > b.tv_nsec" would cause
+   this function to work in some cases where the above assumption is
+   violated, but not in all cases (e.g., a.tv_sec==1, a.tv_nsec==-2,
+   b.tv_sec==0, b.tv_nsec==999999999) and is arguably not worth the
+   extra instructions.  Using a subtraction has the advantage of
+   detecting some invalid cases on platforms that detect integer
+   overflow.
+
+   The (int) cast avoids a gcc -Wconversion warning.  */
+
 static inline int
 timespec_cmp (struct timespec a, struct timespec b)
 {
   return (a.tv_sec < b.tv_sec ? -1
-	  : a.tv_sec > b.tv_sec ? 1
-	  : a.tv_nsec - b.tv_nsec);
+          : a.tv_sec > b.tv_sec ? 1
+          : (int) (a.tv_nsec - b.tv_nsec));
 }
 
 void gettime (struct timespec *);