xref: /freebsd/lib/msun/man/ieee.3 (revision 3a8617a83f16ffc9db4f96e1f0f21af94078e6b1)

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.\"     from: @(#)ieee.3	6.4 (Berkeley) 5/6/91
.\"	$Id: ieee.3,v 1.7 1994/03/10 18:15:07 jtc Exp $
.\"
.Dd Feb 25, 1994
.Dt IEEE 3
.Os
.Sh NAME
.Nm copysign ,
.Nm finite ,
.Nm ilogb ,
.Nm nextafter ,
.Nm remainder ,
.Nm scalbn
.Nd Functions for IEEE arithmetic
.Sh SYNOPSIS
.Fd #include <math.h>
.Ft double
.Fn copysign "double x" "double y"
.Ft int
.Fn finite "double x"
.Ft int
.Fn ilogb "double x"
.Ft double
.Fn nextafter "double x" "double y"
.Ft double
.Fn remainder "double x" "double y"
.Ft double
.Fn scalbn "double x" "int n"
.Sh DESCRIPTION
These functions are required or recommended by
.St -ieee754 .
.Pp
.Fn copysign
returns
.Fa x
with its sign changed to
.Fa y Ns 's.
.Pp
.Fn finite
returns the value 1 just when
\-\*(If \*(Lt
.Fa x
\*(Lt +\*(If;
otherwise a
zero is returned
(when
.Pf \\*(Ba Ns Fa x Ns \\*(Ba
= \*(If or
.Fa x
is \*(Na
.Pp
.Fn ilogb
returns
.Fa x Ns 's exponent
.Fa n ,
in integer format.
.Fn ilogb \*(Pm\*(If
returns
.Dv INT_MAX
and
.Fn ilogb 0
returns
.Dv INT_MIN .
.Pp
.Fn nextafter
returns the next machine representable number from
.Fa x
in direction
.Fa y .
.Pp
.Fn remainder
returns the remainder
.Fa r
:=
.Fa x
\-
.Fa n\(**y
where
.Fa n
is the integer nearest the exact value of
.Bk -words
.Fa x Ns / Ns Fa y ;
.Ek
moreover if
.Pf \\*(Ba Fa n
\-
.Sm off
.Fa x No / Fa y No \\*(Ba
.Sm on
=
1/2
then
.Fa n
is even.  Consequently
the remainder is computed exactly and
.Sm off
.Pf \\*(Ba Fa r No \\*(Ba
.Sm on
\*(Le
.Sm off
.Pf \\*(Ba Fa y No \\*(Ba/2.
.Sm on
But
.Fn remainder x 0
and
.Fn remainder \*(If 0
are invalid operations that produce a \*(Na.
.Pp
.Fn scalbn
returns
.Fa x Ns \(**(2** Ns Fa n )
computed by exponent manipulation.
.Sh SEE ALSO
.Xr math 3
.Sh HISTORY
The
.Nm ieee
functions appeared in
.Bx 4.3 .
.Sh STANDARDS
.St -ieee754