/C

# asin, asinf, asinl

Defined in header `<math.h>`
`float       asinf( float arg );`
(1) (since C99)
`double      asin( double arg );`
(2)
`long double asinl( long double arg );`
(3) (since C99)
Defined in header `<tgmath.h>`
`#define asin( arg )`
(4) (since C99)
1-3) Computes the principal values of the arc sine of `arg`.
4) Type-generic macro: If the argument has type `long double`, `asinl` is called. Otherwise, if the argument has integer type or the type `double`, `asin` is called. Otherwise, `asinf` is called. If the argument is complex, then the macro invokes the corresponding complex function (`casinf`, `casin`, `casinl`).

### Parameters

 arg - floating point value

### Return value

If no errors occur, the arc sine of `arg` (arcsin(arg)) in the range [-
 π 2
; +
 π 2
], is returned.

If a domain error occurs, an implementation-defined value is returned (NaN where supported).

If a range error occurs due to underflow, the correct result (after rounding) is returned.

### Error handling

Errors are reported as specified in math_errhandling.

Domain error occurs if `arg` is outside the range `[-1.0; 1.0]`.

If the implementation supports IEEE floating-point arithmetic (IEC 60559),

• If the argument is ±0, it is returned unmodified
• If |arg| > 1, a domain error occurs and NaN is returned.
• if the argument is NaN, NaN is returned

### Example

```#include <math.h>
#include <stdio.h>
#include <errno.h>
#include <fenv.h>
#include <string.h>

#pragma STDC FENV_ACCESS ON
int main(void)
{
printf("asin( 1.0) = %+f, 2*asin( 1.0)=%+f\n", asin(1), 2*asin(1));
printf("asin(-0.5) = %+f, 6*asin(-0.5)=%+f\n", asin(-0.5), 6*asin(-0.5));
// special values
printf("asin(0.0) = %1f, asin(-0.0)=%f\n", asin(+0.0), asin(-0.0));
// error handling
errno = 0; feclearexcept(FE_ALL_EXCEPT);
printf("asin(1.1) = %f\n", asin(1.1));
if(errno == EDOM) perror("    errno == EDOM");
if(fetestexcept(FE_INVALID)) puts("    FE_INVALID raised");
}```

Possible output:

```asin( 1.0) = +1.570796, 2*asin( 1.0)=+3.141593
asin(-0.5) = -0.523599, 6*asin(-0.5)=-3.141593
asin(0.0) = 0.000000, asin(-0.0)=-0.000000
asin(1.1) = nan
errno == EDOM: Numerical argument out of domain
FE_INVALID raised```

### References

• C11 standard (ISO/IEC 9899:2011):
• 7.12.4.2 The asin functions (p: 238)
• 7.25 Type-generic math <tgmath.h> (p: 373-375)
• F.10.1.2 The asin functions (p: 518)
• C99 standard (ISO/IEC 9899:1999):
• 7.12.4.2 The asin functions (p: 219)
• 7.22 Type-generic math <tgmath.h> (p: 335-337)
• F.9.1.2 The asin functions (p: 456)
• C89/C90 standard (ISO/IEC 9899:1990):
• 4.5.2.2 The asin function