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.\"     @(#)isinf.3	8.2 (Berkeley) 1/29/94
.\"
.Dd September 27, 2017
.Dt ISINF 3
.Os
.Sh NAME
.Nm isinf
.Nd test for infinity
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In math.h
.Ft int
.Fn isinf "real-floating x"
.Sh DESCRIPTION
The
.Fn isinf
macro determines whether its argument
.Fa x
is an infinity (positive or negative).
An argument represented in a format wider than its semantic type is
converted to its semantic type first.
The determination is then based on the type of the argument.
.Sh RETURN VALUES
The
.Fn isinf
macro returns a non-zero value if the value of
.Fa x
is an infinity.
Otherwise 0 is returned.
.Sh SEE ALSO
.Xr fpclassify 3 ,
.Xr isfinite 3 ,
.Xr isinff 3 ,
.Xr isnan 3 ,
.Xr isnanf 3 ,
.Xr isnormal 3 ,
.Xr math 3 ,
.Xr signbit 3
.Rs
.%T "IEEE Standard for Binary Floating-Point Arithmetic"
.%Q ANSI
.%R Std 754-1985
.Re
.Sh STANDARDS
The
.Fn isinf
macro conforms to
.St -isoC-99 .
.Sh CAVEATS
On VAX the
.Fn isinf
function always returns 0,
as the architecture doesn't have a representation for infinity.