.\"	$NetBSD: mstohz.9,v 1.12 2019/09/28 15:11:19 christos Exp $
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.\" Copyright (c) 2002 Manuel Bouyer.
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.Dd September 28, 2019
.Dt MSTOHZ 9
.Os
.Sh NAME
.Nm mstohz ,
.Nm hztoms
.Nd convert between milliseconds and system clock ticks
.Sh SYNOPSIS
.In sys/param.h
.Ft unsigned int
.Fn mstohz "unsigned int ms"
.Ft unsigned int
.Fn hztoms "unsigned int hz"
.Sh DESCRIPTION
The
.Fn mstohz
macro can be used to convert time
in milliseconds to system clock ticks, as used
by the
.Xr callout 9
facility, in an integer-overflow safe way.
Conversely,
.Fn hztoms
converts system clock ticks to milliseconds.
.Pp
These macros are defined in the
.Aq Em sys/param.h
header.
Individual ports can have a processor-specific, more efficient
version implemented in their
.Aq Em machine/param.h
header as a define.
.Sh RETURN VALUES
The return value is either the number of clock ticks or milliseconds
for the specified value.
.Sh SEE ALSO
.Xr param 3 ,
.Xr callout 9 ,
.Xr tvtohz 9
.Sh BUGS
Neither
.Fn mstohz
nor
.Fn hztoms
make use of expensive 64-bit integer arithmetic.
The result from
.Fn mstohz
will be rounded down to one second if the parameter is larger
than 131072 milliseconds.