LOG1P(3P)

💖 LOG1P(3P) — the POSIX Programmer's Manual page, but make it cute 💖

okay bestie, quick heads-up before we dive in: this page lives in the POSIX Programmer's Manual, k? Which means the Linux implementation of this interface may differ (so go peek at the matching Linux manual page for the deets on Linux behavior), or — plot twist — the interface might not even be implemented on Linux at all. 🙈

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✨ PROLOG ✨

This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.

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🎀 NAME 🎀

log1p, log1pf, log1pl — compute a natural logarithm. that's the whole vibe, she's a math girlie 💅

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🌸 SYNOPSIS 🌸

#include <math.h>

double log1p(double x);
float log1pf(float x);
long double log1pl(long double x);

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🦋 DESCRIPTION 🦋

so the functionality described on this reference page is aligned with the ISO C standard, periodt. Any conflict between the requirements described here and the ISO C standard is unintentional, no cap. This volume of POSIX.1‐2017 defers to the ISO C standard — ISO C is the main character here, we're just supporting cast. 👑

These functions shall compute log_e(1.0 + x).

Now, if your application wants to check for error situations (iconic, responsible behavior, we love that), you should set errno to zero and call feclearexcept(FE_ALL_EXCEPT) before calling these functions. Then on return, if errno is non-zero, or fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero — boom, an error has occurred. 💀

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⭐ RETURN VALUE ⭐

Upon successful completion, these functions shall return the natural logarithm of 1.0 + x. slay. 💖

If x is -1, a pole error shall occur and log1p(), log1pf(), and log1pl() shall return -HUGE_VAL, -HUGE_VALF, and -HUGE_VALL, respectively.

For finite values of x that are less than -1, or if x is -Inf, 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, or +Inf, x shall be returned.

If x is subnormal, a range error may occur and x should be returned.

If x is not returned, log1p(), log1pf(), and log1pl() 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 finite value of x is less than -1, or x 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 value of x 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.

The following sections are informative. (iykyk — informative means it's the bonus content, not the binding rules 🫶)

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🌈 EXAMPLES 🌈

None. — literally nothing here bestie, the example girlies did not show up to the function today 😭

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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. that's the rule, fr fr.

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🧚 RATIONALE 🧚

None. — empty, void, giving minimalist queen energy ✨

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💜 FUTURE DIRECTIONS 💜

None. — the future is a blank canvas, and she's not filling it in 🦋

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👑 SEE ALSO 👑

• feclearexcept()
• fetestexcept()
• log()

Also: 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!! 🎀✨ thank you for coming to my ted talk, you understood the assignment 💅

this little masterpiece came to you courtesy of IEEE/The Open Group, dated 2017, and yeah she answers to the name LOG1P(3P) 💖 go forth and compute your natural logs, mwah 😘