NAME

cacos, cacosf, cacosl — complex arc cosine functions

SYNOPSIS

#include <complex.h>

double complex cacos(double complex z);
float complex cacosf(float complex z);
long double complex cacosl(long double complex z);


DESCRIPTION

^[CX] The functionality described on this reference page is aligned with the ISO C standard. Any conflict between the requirements described here and the ISO C standard is unintentional. This volume of POSIX.1-2024 defers to the ISO C standard.

These functions shall compute the complex arc cosine of z, with branch cuts outside the interval [-1, +1] along the real axis.

RETURN VALUE

These functions shall return the complex arc cosine value, in the range of a strip mathematically unbounded along the imaginary axis and in the interval [0, ℼ] along the real axis.

^[MXC] cacos(conj(z)), cacosf(conjf(z)), and cacosl(conjl(z)) shall return exactly the same value as conj(cacos(z)), conjf(cacosf(z)), and conjl(cacosl(z)), respectively, including for the special values of z below.

If z is ±0 + i0, ℼ/2 - i0 shall be returned.

If z is ±0 + iNaN, ℼ/2 + iNaN shall be returned.

If z is x + iInf where x is finite, ℼ/2 - iInf shall be returned.

If z is x + iNaN where x is non-zero and finite, NaN + iNaN shall be returned and the invalid floating-point exception may be raised.

If z is -Inf + iy where y is positive-signed and finite, ℼ - iInf shall be returned.

If z is +Inf + iy where y is positive-signed and finite, +0 - iInf shall be returned.

If z is -Inf + iInf, 3ℼ/4 - iInf shall be returned.

If z is +Inf + iInf, ℼ/4 - iInf shall be returned.

If z is ±Inf + iNaN, NaN ± iInf shall be returned; the sign of the imaginary part of the result is unspecified.

If z is NaN + iy where y is finite, NaN + iNaN shall be returned and the invalid floating-point exception may be raised.

If z is NaN + iInf, NaN - iInf shall be returned.

If z is NaN + iNaN, NaN - iNaN shall be returned.

ERRORS

No errors are defined.

EXAMPLES

None.

APPLICATION USAGE

None.

RATIONALE

None.

FUTURE DIRECTIONS

None.

SEE ALSO

ccos

XBD <complex.h>

CHANGE HISTORY

First released in Issue 6. Derived from the ISO/IEC 9899:1999 standard.

Issue 8

Austin Group Defect 1302 is applied, aligning these functions with the ISO/IEC 9899:2018 standard.