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.Dd April 1, 2017
.Dt COSPI 3
.Os
.Sh NAME
.Nm cospi ,
.Nm cospif ,
.Nm cospil
.Nd half\(encycle cosine functions
.Sh LIBRARY
.Lb libm
.Sh SYNOPSIS
.In math.h
.Ft double
.Fn cospi "double x"
.Ft float
.Fn cospif "float x"
.Ft long double
.Fn cospil "long double x"
.Sh DESCRIPTION
The
.Fn cospi ,
.Fn cospif ,
and
.Fn cospil
functions compute the cosine of
.Fa "\(*p \(mu x" .
and measure angles in half-cycles.
.Sh RETURN VALUES
The
.Fn cospi ,
.Fn cospif ,
and
.Fn cospil
functions returns
.Fn cos "\(*p \(mu x" .
If \*(Bax\*(Ba \*(Ge 2^(p - 1)
where p is the floating\(enpoint precision of
.Ar x ,
then the returned value is 1 and it has no significance.
.Sh SPECIAL VALUES
.Bl -tag
.It
.Fn cospi \*(Pm0
returns 1.
.It
.Fn cospi \*(Pmn/2
returns 0 for positive integers
.Ar n .
.It
.Fn cospi n
returns 1 for even integers
.Ar n .
.It
.Fn cospi n
returns \-1 for odd integers
.Ar n .
.It
.Fn cospi \*(Pm\(if
return an \*(Na and raises an FE_INVALID exception.
.It
.Fn cospi \*(Na
return an \*(Na and raises an FE_INVALID exception.
.El
.Sh SEE ALSO
.Xr cos 3 ,
.Xr fenv 3 ,
.Xr math 3 ,
.Xr sin 3 ,
.Xr sinpi 3 ,
.Xr tan 3 ,
.Xr tanpi 3
.Sh AUTHORS
The half\(encycle trignometric functions were written by
.An Steven G. Kargl Aq Mt kargl@FreeBSD.org .
.Sh STANDARDS
These functions conform to
IEEE Std 754\(tm\(en2008 ,
\(dqIEEE Standard for Floating-Point Arithmetic\(dq
and to
ISO/IEC TS 18661-4 ,
\(dqInformation technology \(em Programming languages, their environments,
and system software interfaces \(em Floating\(enpoint extensions for
C\(dq \(em Part 4: Supplementary functions.