# asin, asinf, asinl

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< c‎ | numeric‎ | math

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)
_Decimal32 asind32( _Decimal32 arg ); | (4) | (since C23)
_Decimal64 asind64( _Decimal64 arg ); | (5) | (since C23)
_Decimal128 asind128( _Decimal128 arg ); | (6) | (since C23)
Defined in header `<tgmath.h>` |  |
#define asin( arg ) | (7) | (since C99)

1-6) Computes the principal values of the arc sine of arg.
7) Type-generic macro: If the argument has type long double, (3) (`asinl`) is called. Otherwise, if the argument has integer type or the type double, (2) (`asin`) is called. Otherwise, (1) (`asinf`) is called. If the argument is complex, then the macro invokes the corresponding complex function (casinf, casin, casinl).

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

### 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

Run this code

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

    #ifndef __GNUC__
    #pragma STDC FENV_ACCESS ON
    #endif

    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

- C23 standard (ISO/IEC 9899:2023):

  - 7.12.4.2 The asin functions (p: TBD)

  - 7.25 Type-generic math <tgmath.h> (p: TBD)

  - F.10.1.2 The asin functions (p: TBD)

- C17 standard (ISO/IEC 9899:2018):

  - 7.12.4.2 The asin functions (p: 174)

  - 7.25 Type-generic math <tgmath.h> (p: 272-273)

  - F.10.1.2 The asin functions (p: 378)

- 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

### See also

acos acosf acosl (C99)(C99) | computes arc cosine (\({\small\arccos{x} }\)arccos(x)) (function)
atan atanf atanl (C99)(C99) | computes arc tangent (\({\small\arctan{x} }\)arctan(x)) (function)
atan2 atan2f atan2l (C99)(C99) | computes arc tangent, using signs to determine quadrants (function)
sin sinf sinl (C99)(C99) | computes sine (\({\small\sin{x} }\)sin(x)) (function)
casin casinf casinl (C99)(C99)(C99) | computes the complex arc sine (function)

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