cospi, cospif, cospil, cospid32, cospid64, cospid128
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Defined in header
<math.h>
float cospif( float arg );
(1)
(since C23)
double cospi( double arg );
(2)
(since C23)
long double cospil( long double arg );
(3)
(since C23)
_Decimal32 cospid32( _Decimal32 arg );
(4)
(since C23)
_Decimal64 cospid64( _Decimal64 arg );
(5)
(since C23)
_Decimal128 cospid128( _Decimal128 arg );
(6)
(since C23)
Defined in header
<tgmath.h>
#define cospi( arg )
(7)
(since C23)
1-6) Computes the cosine of
π·arg measured in radians, thus regarding arg as a measurement in half-revolutions.7) Type-generic macro: calls the correct function based on the type of arg. If the argument has integer type, (2) (
cospi) is called.The functions (4-6) are declared if and only if the implementation predefines __STDC_IEC_60559_DFP__ (i.e. the implementation supports decimal floating-point numbers).
[edit] Parameters
arg
-
floating-point value whose product with
π represents an angle in radians
[edit] Return value
If no errors occur, the cosine of π·arg (cos(π×arg)) in the range [-1, +1], is returned.
[edit] Error handling
Errors are reported as specified in math_errhandling.
If the implementation supports IEEE floating-point arithmetic (IEC 60559):
- if the argument is ±0, the result is 1.0;
- if the argument is ±∞, NaN is returned and FE_INVALID is raised;
- if the argument is NaN, NaN is returned.
[edit] Example
Run this code
#include <errno.h> #include <fenv.h> #include <math.h> #include <stdio.h> #ifndef __GNUC__ #pragma STDC FENV_ACCESS ON #endif #if __STDC_VERSION__ < 202311L // A naive implementation of a subset of cospi family double cospi(double arg) { return cos (arg * (double)3.1415926535897932384626433); } #endif int main(void) { const double pi = acos (-1); // typical usage printf ("cospi(1) = %f, cos(pi) = %f\n", cospi(1), cos (pi)); printf ("cospi(0.5) = %f, cos(pi/2) = %f\n", cospi(0.5), cos (pi / 2)); printf ("cospi(-0.75) = %f, cos(-3*pi/4) = %f\n", cospi(-0.75), cos (-3 * pi / 4)); // special values printf ("cospi(+0) = %f\n", cospi(0.0)); printf ("cospi(-0) = %f\n", cospi(-0.0)); // error handling feclearexcept (FE_ALL_EXCEPT ); printf ("cospi(INFINITY) = %f\n", cospi(INFINITY)); if (fetestexcept (FE_INVALID )) puts (" FE_INVALID raised"); }
Possible output:
cospi(1) = -1.000000, cos(pi) = -1.000000 cospi(0.5) = 0.000000, cos(pi/2) = 0.000000 cospi(-0.75) = -0.707107, cos(-3*pi/4) = -0.707107 cospi(+0) = 1.000000 cospi(-0) = 1.000000 cospi(INFINITY) = -nan FE_INVALID raised
[edit] References
- C23 standard (ISO/IEC 9899:2024):
- 7.12.4.12 The cospi functions (p: 247)
- 7.27 Type generic math <tgmath.h> (p: 387)