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+.\" Copyright (c) 2007 by Michael Kerrisk <mtk.manpages@gmail.com>
+.\"
+.\" SPDX-License-Identifier: Linux-man-pages-copyleft
+.\"
+.\" 2007-07-31, mtk, Created
+.\"
+.TH timeradd 3 (date) "Linux man-pages (unreleased)"
+.SH NAME
+timeradd, timersub, timercmp, timerclear, timerisset \- timeval operations
+.SH LIBRARY
+Standard C library
+.RI ( libc ", " \-lc )
+.SH SYNOPSIS
+.nf
+.B #include <sys/time.h>
+.P
+.BI "void timeradd(struct timeval *" a ", struct timeval *" b ,
+.BI "              struct timeval *" res );
+.BI "void timersub(struct timeval *" a ", struct timeval *" b ,
+.BI "              struct timeval *" res );
+.P
+.BI "void timerclear(struct timeval *" tvp );
+.BI "int timerisset(struct timeval *" tvp );
+.P
+.BI "int timercmp(struct timeval *" a ", struct timeval *" b ", " CMP );
+.fi
+.P
+.RS -4
+Feature Test Macro Requirements for glibc (see
+.BR feature_test_macros (7)):
+.RE
+.P
+All functions shown above:
+.nf
+    Since glibc 2.19:
+        _DEFAULT_SOURCE
+    glibc 2.19 and earlier:
+        _BSD_SOURCE
+.fi
+.SH DESCRIPTION
+The macros are provided to operate on
+.I timeval
+structures, defined in
+.I <sys/time.h>
+as:
+.P
+.in +4n
+.EX
+struct timeval {
+    time_t      tv_sec;     /* seconds */
+    suseconds_t tv_usec;    /* microseconds */
+};
+.EE
+.in
+.P
+.BR timeradd ()
+adds the time values in
+.I a
+and
+.IR b ,
+and places the sum in the
+.I timeval
+pointed to by
+.IR res .
+The result is normalized such that
+.I res\->tv_usec
+has a value in the range 0 to 999,999.
+.P
+.BR timersub ()
+subtracts the time value in
+.I b
+from the time value in
+.IR a ,
+and places the result in the
+.I timeval
+pointed to by
+.IR res .
+The result is normalized such that
+.I res\->tv_usec
+has a value in the range 0 to 999,999.
+.P
+.BR timerclear ()
+zeros out the
+.I timeval
+structure pointed to by
+.IR tvp ,
+so that it represents the Epoch: 1970-01-01 00:00:00 +0000 (UTC).
+.P
+.BR timerisset ()
+returns true (nonzero) if either field of the
+.I timeval
+structure pointed to by
+.I tvp
+contains a nonzero value.
+.P
+.BR timercmp ()
+compares the timer values in
+.I a
+and
+.I b
+using the comparison operator
+.IR CMP ,
+and returns true (nonzero) or false (0) depending on
+the result of the comparison.
+Some systems (but not Linux/glibc),
+have a broken
+.BR timercmp ()
+implementation,
+.\" HP-UX, Tru64, Irix have a definition like:
+.\"#define timercmp(tvp, uvp, cmp) \
+.\"    ((tvp)->tv_sec cmp (uvp)->tv_sec || \
+.\"    (tvp)->tv_sec == (uvp)->tv_sec && (tvp)->tv_usec cmp (uvp)->tv_usec)
+in which
+.I CMP
+of
+.IR >= ,
+.IR <= ,
+and
+.I ==
+do not work;
+portable applications can instead use
+.P
+.in +4n
+.EX
+!timercmp(..., <)
+!timercmp(..., >)
+!timercmp(..., !=)
+.EE
+.in
+.SH RETURN VALUE
+.BR timerisset ()
+and
+.BR timercmp ()
+return true (nonzero) or false (0).
+.SH ERRORS
+No errors are defined.
+.SH STANDARDS
+None.
+.SH HISTORY
+BSD.
+.SH SEE ALSO
+.BR gettimeofday (2),
+.BR time (7)