sinpi, sinpif, sinpil, sinpid32, sinpid64, sinpid128

Defined in header `<math.h>`
`float sinpif( float arg );`	(1)	(since C23)
`double sinpi( double arg );`	(2)	(since C23)
`long double sinpil( long double arg );`	(3)	(since C23)
`_Decimal32 sinpid32( _Decimal32 arg );`	(4)	(since C23)
`_Decimal64 sinpid64( _Decimal64 arg );`	(5)	(since C23)
`_Decimal128 sinpid128( _Decimal128 arg );`	(6)	(since C23)
Defined in header `<tgmath.h>`
`#define sinpi( arg )`	(7)	(since C23)

1-6) Computes the sine 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) 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)

Parameters

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

Return value

If no errors occur, the sine of π·arg (sin(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, it is returned unmodified;
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 sinpi family
double sinpi(double arg)
{
    return sin(arg * (double)3.1415926535897932384626433);
}
#endif
 
int main(void)
{
    const double pi = acos(-1);
 
    // typical usage
    printf("sinpi(1) = %f, sin(pi) = %f\n", sinpi(1), sin(pi));
    printf("sinpi(0.5) = %f, sin(pi/2) = %f\n", sinpi(0.5), sin(pi / 2));
    printf("sinpi(-0.75) = %f, sin(-3*pi/4) = %f\n", sinpi(-0.75), sin(-3 * pi / 4));
 
    // special values
    printf("sinpi(+0) = %f\n", sinpi(0.0));
    printf("sinpi(-0) = %f\n", sinpi(-0.0));
 
    // error handling
    feclearexcept(FE_ALL_EXCEPT);
    printf("sinpi(INFINITY) = %f\n", sinpi(INFINITY));
    if (fetestexcept(FE_INVALID))
        puts("    FE_INVALID raised");
}

Possible output:

sinpi(1) = 0.000000, sin(pi) = 0.000000
sinpi(0.5) = 1.000000, sin(pi/2) = 1.000000
sinpi(-0.75) = -0.707107, sin(-3*pi/4) = -0.707107
sinpi(+0) = 0.000000
sinpi(-0) = -0.000000
sinpi(INFINITY) = -nan
    FE_INVALID raised

References

C23 standard (ISO/IEC 9899:2023):

7.12.4.13 The sinpi functions (p: 247-248)
7.27 Type generic math <tgmath.h> (p: 387)

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