__cospi(3) BSD Library Functions Manual __cospi(3)
NAME
__cospi -- cosine-pi function
SYNOPSIS
#include <math.h>
float
__cospif(float x);
double
__cospi(double x);
DESCRIPTION
The __cospi() function returns the cosine of pi times x (measured in
radians). This can be computed more accurately than cos(M_PI * x),
because it can implicitly use as many bits of pi as are necessary to
deliver a well-rounded result, instead of the 53-bits to which M_PI is
limited. For large x it may also be more efficient, as the argument
reduction involved is significantly simpler.
This function may be especially useful for working with degrees; whereas
cos(M_PI * x / 180.0) cannot produce exact results for angles that
naively "should" be exact, like 90 degrees, __cospi(x / 180.0) can be
computed exactly.
SPECIAL VALUES
__cospi(-x) is the same as __cospi(x) for any finite x.
__cospi(n) returns +1 for any even integer n.
__cospi(n) returns -1 for any odd integer n.
__cospi(n + 0.5) returns +0 for any integer n.
__cospi(+-infinity) raises the invalid floating-point exception and
returns NaN.
VECTOR OPERATIONS
If you need to apply the __cospi() function to SIMD vectors or arrays,
using the following functions provided by the Accelerate.framework may be
useful:
#include <Accelerate/Accelerate.h>
vFloat vcospif(vFloat x);
void vvcospif(float *y, float *x, const int n);
void vvcospi(double *y, double *x, const int n);
SEE ALSO
__sinpi(3), __tanpi(3), __sincospi(3), math(3)
BSD December 15, 2012 BSD
Mac OS X 10.9.1 - Generated Fri Jan 10 05:47:31 CST 2014