NAME

cospi, cospif, cospil — half–cycle cosine functions

LIBRARY

Math Library (libm, -lm)

SYNOPSIS

#include <math.h>

double
cospi(double x);

float
cospif(float x);

long double
cospil(long double x);

DESCRIPTION

The cospi(), cospif(), and cospil() functions compute the cosine of π × x. and measure angles in half-cycles.

RETURN VALUES

The cospi(), cospif(), and cospil() functions returns cos(π × x). If |x| ≥ 2^(p - 1) where p is the floating–point precision of x, then the returned value is 1 and it has no significance.

SPECIAL VALUES

cospi(±0) returns 1.

cospi(±n/2) returns 0 for positive integers n.

cospi(n) returns 1 for even integers n.

cospi(n) returns -1 for odd integers n.

cospi(±∞) return an NaN and raises an FE_INVALID exception.

cospi(NaN) return an NaN and raises an FE_INVALID exception.

SEE ALSO

cos(3), fenv(3), math(3), sin(3), sinpi(3), tan(3), tanpi(3)

AUTHORS

The half–cycle trignometric functions were written by Steven G. Kargl <kargl@FreeBSD.org>.

STANDARDS

These functions conform to IEEE Std 754™–2008 , "IEEE Standard for Floating-Point Arithmetic" and to ISO/IEC TS 18661-4 , "Information technology — Programming languages, their environments, and system software interfaces — Floating–point extensions for C" — Part 4: Supplementary functions.