.\" Copyright (c) 1999 Kelly Yancey <kbyanc@posi.net>
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.\" $FreeBSD: head/share/man/man3/timeradd.3 119893 2003-09-08 19:57:22Z ru $
.\"
.Dd August 11, 1999
.Dt TIMERADD 3
.Os
.Sh NAME
.Nm timeradd ,
.Nm timersub ,
.Nm timerclear ,
.Nm timerisset ,
.Nm timercmp
.Nd operations on timevals
.Sh SYNOPSIS
.In sys/time.h
.Ft void
.Fn timeradd "struct timeval *a" "struct timeval *b" "struct timeval *res"
.Ft void
.Fn timersub "struct timeval *a" "struct timeval *b" "struct timeval *res"
.Ft void
.Fn timerclear "struct timeval *tvp"
.Ft int
.Fn timerisset "struct timeval *tvp"
.Ft int
.Fn timercmp "struct timeval *a" "struct timeval *b" CMP
.Sh DESCRIPTION
These macros are provided for manipulating
.Fa timeval
structures for use with the
.Xr gettimeofday 2
and
.Xr settimeofday 2
calls.
The structure is defined in
.In sys/time.h
as:
.Bd -literal
struct timeval {
	long	tv_sec;		/* seconds since Jan. 1, 1970 */
	long	tv_usec;	/* and microseconds */
};
.Ed
.Pp
.Fn timeradd
adds the time information stored in
.Fa a
to
.Fa b
and stores the resulting
.Vt timeval
in
.Fa res .
The results are simplified such that the value of
.Fa res->tv_usec
is always less than 1,000,000 (1 second).
.Pp
.Fn timersub
subtracts the time information stored in
.Fa b
from
.Fa a
and stores the resulting
.Vt timeval
in
.Fa res .
.Pp
.Fn timerclear
initializes
.Fa tvp
to midnight (0 hour) January 1st, 1970 (the Epoch).
.Pp
.Fn timerisset
returns true if
.Fa tvp
is set to any time value other than the Epoch.
.Pp
.Fn timercmp
compares
.Fa a
to
.Fa b
using the comparison operator given in
.Fa CMP ,
and returns the result of that comparison.
.Sh SEE ALSO
.Xr gettimeofday 2
.Sh HISTORY
The
.Fn timeradd
family of macros were imported from
.Nx 1.1 ,
and appeared in
.Fx 2.2.6 .