ATANH(3P)

💖 ATANH(3P) — bestie edition 💖

okay so real talk, this is the POSIX Programmer's Manual page for atanh, and before we even get into it there's a little heads-up situation.

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✨ PROLOG ✨

So this page? It's part of the POSIX Programmer's Manual. That means the Linux version of this interface might be a whole different vibe (so pls go check the matching Linux manual page if you need the tea on Linux behavior specifically), or honestly? It might not even be implemented on Linux at all. no cap. 🙈

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🌸 NAME 🌸

atanh, atanhf, atanhl — the inverse hyperbolic tangent functions. the trio. the icons. 💅

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🎀 SYNOPSIS 🎀

#include <math.h>

double atanh(double x);
float atanhf(float x);
long double atanhl(long double x);

like, one include, three flavors. pick your fave. 🦋

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💜 DESCRIPTION 💜

So the functionality described on this reference page is aligned with the ISO C standard. And if there's ever any conflict between what's written here and the ISO C standard? That's unintentional, fr fr. This volume of POSIX.1‐2017 defers to the ISO C standard. so the ISO C standard is the main character here, periodt. 👑

These functions shall compute the inverse hyperbolic tangent of their argument x. that's the whole job bestie. ✨

Now — if an application wants to check for error situations (and honestly, we love a responsible queen who checks), it should set errno to zero and call feclearexcept(FE_ALL_EXCEPT) before calling these functions. Then on return: if errno is non-zero, OR if fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, then boom — an error has occurred. 😭

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🔥 RETURN VALUE 🔥

Upon successful completion, these functions shall return the inverse hyperbolic tangent of their argument. slay. 💖

okay but now the drama, let's get into the edge cases because there are several:

• If x is ±1, a pole error shall occur, and atanh(), atanhf(), and atanhl() shall return the value of the macro HUGE_VAL, HUGE_VALF, and HUGE_VALL, respectively, with the same sign as the correct value of the function. 💀
• For finite |x|>1, a domain error shall occur, and either a NaN (if supported), or an implementation-defined value shall be returned.
• If x is NaN, a NaN shall be returned.
• If x is ±0, x shall be returned. (a lil no-op moment, we love that for us 🫶)
• If x is ±Inf, a domain error shall occur, and a NaN shall be returned.
• If x is subnormal, a range error may occur and x should be returned.
• If x is not returned, atanh(), atanhf(), and atanhl() shall return an implementation-defined value no greater in magnitude than DBL_MIN, FLT_MIN, and LDBL_MIN, respectively.

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😤 ERRORS 😤

These functions shall fail if:

• Domain Error — The x argument is finite and not in the range [-1,1], or is ±Inf.

If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then errno shall be set to [EDOM]. If the integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero, then the invalid floating-point exception shall be raised.

• Pole Error — The x argument is ±1.

If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then errno shall be set to [ERANGE]. If the integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero, then the divide-by-zero floating-point exception shall be raised.

These functions may fail if:

• Range Error — The value of x is subnormal.

If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then errno shall be set to [ERANGE]. If the integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero, then the underflow floating-point exception shall be raised.

also a lil note: the following sections are informative. just so you know. 💫

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🍓 EXAMPLES 🍓

None. that's it. that's the section. we move. 💀

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🌈 APPLICATION USAGE 🌈

On error, the expressions (math_errhandling & MATH_ERRNO) and (math_errhandling & MATH_ERREXCEPT) are independent of each other, but at least one of them must be non-zero. so like, they don't need each other, but one of them has to show up to the party. iykyk. 🎀

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🧚 RATIONALE 🧚

None. iconic of it honestly. nothing to explain. ✨

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⭐ FUTURE DIRECTIONS ⭐

None. the future is a mystery, bestie. we love an open ending. 🦋

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👑 SEE ALSO 👑

• feclearexcept()
• fetestexcept()
• tanh()

The Base Definitions volume of POSIX.1‐2017, Section 4.20, Treatment of Error Conditions for Mathematical Functions, <math.h>

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💅 COPYRIGHT 💅

Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .

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and that's the whole page bestie!! 🫶 brought to you by IEEE/The Open Group, 2017, closing out the ATANH(3P) chapter like the absolute icon it is. go forth and compute those inverse hyperbolic tangents. mwah. 💖✨🎀🦋