cospi, cospif, cospil, cospid32, cospid64, cospid128

< c‎ | numeric‎ | math

Common mathematical functions
Types
 div_tldiv_tlldiv_timaxdiv_t(C99)(C99)
 float_tdouble_t(C99)(C99) _Decimal32_t_Decimal64_t(C23)(C23)
Functions
Basic operations
 abslabsllabsimaxabs(C99)(C99) fabs divldivlldivimaxdiv(C99)(C99)
 fmod remainder(C99) remquo(C99) fma(C99) fdim(C99) nannanfnanlnandN(C99)(C99)(C99)(C23)
Maximum/minimum operations
 fmax(C99) fmaximum(C23) fmaximum_mag(C23) fmaximum_num(C23) fmaximum_mag_num(C23)
 fmin(C99) fminimum(C23) fminimum_mag(C23) fminimum_num(C23) fminimum_mag_num(C23)
Exponential functions
 exp exp10(C23) exp2(C99) expm1(C99) exp10m1(C23) exp2m1(C23)
 log log10 log2(C99) log1plogp1(C99)(C23) log10p1(C23) log2p1(C23)
Power functions
 sqrt cbrt(C99) rootn(C23) rsqrt(C23)
 hypot(C99) compound(C23) pow pown(C23) powr(C23)
Trigonometric and hyperbolic functions
 sin cos tan asin acos atan atan2 sinpi(C23) cospi(C23) tanpi(C23)
 asinpi(C23) acospi(C23) atanpi(C23) atan2pi(C23) sinh cosh tanh asinh(C99) acosh(C99) atanh(C99)
Error and gamma functions
 erf(C99) erfc(C99)
 lgamma(C99) tgamma(C99)
Nearest integer floating-point operations
 ceil floor roundlroundllround(C99)(C99)(C99) roundeven(C23) trunc(C99)
 nearbyint(C99) rintlrintllrint(C99)(C99)(C99) fromfpfromfpxufromfpufromfpx(C23)(C23)(C23)(C23)
Floating-point manipulation functions
 ldexp frexp scalbnscalbln(C99)(C99) ilogbllogb(C99)(C23) logb(C99)
 modf nextafternexttoward(C99)(C99) nextupnextdown(C23)(C23) copysign(C99) canonicalize(C23)
Narrowing operations
 fdiv(C23) ffma(C23) fsqrt(C23)
Quantum and quantum exponent functions
 quantizedN(C23) samequantumdN(C23)
 quantumdN(C23) llquantexpdN(C23)
Decimal re-encoding functions
 encodedecdN(C23) decodedecdN(C23)
 encodebindN(C23) decodebindN(C23)
Classification
 fpclassify(C99) iscanonical(C23) isfinite(C99) isinf(C99) isnan(C99) isnormal(C99) signbit(C99) issubnormal(C23) iszero(C23)
 isgreater(C99) isgreaterequal(C99) isless(C99) islessequal(C99) islessgreater(C99) isunordered(C99) issignaling(C23) iseqsig(C23)
Macro constants
Special floating-point values
 HUGE_VALFHUGE_VALHUGE_VALLHUGE_VALDN(C99)(C99)(C23)
 INFINITYDEC_INFINITY(C99)(C23) NANDEC_NAN(C99)(C23)
Arguments and return values
 FP_ILOGB0FP_ILOGBNAN(C99)(C99) FP_INT_UPWARDFP_INT_DOWNWARDFP_INT_TOWARDZEROFP_INT_TONEARESTFROMZEROFP_INT_TONEAREST(C23)(C23)(C23)(C23)(C23)
 FP_LLOGB0FP_LLOGBNAN(C23)(C23) FP_NORMALFP_SUBNORMALFP_ZEROFP_INFINITEFP_NAN(C99)(C99)(C99)(C99)(C99)
Error handling
 MATH_ERRNOMATH_ERRNOEXCEPT(C99)(C99)
 math_errhandling(C99)
Fast operation indicators

 Defined in header  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  #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). (since C23)

Contents

Parameters

 arg - floating-point value whose product with π represents an angle in radians

Return value

If no errors occur, the cosine of π·arg (cos(π×arg)) in the range [-1, +1], is returned.

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.

Example

#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

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)