EXPM1(3P)

✨ EXPM1(3P) — bestie edition ✨

okay so this is the POSIX Programmer's Manual page for expm1, expm1f, expm1l (yes, the manual name is right there, i'm folding it in, we move 🫶).

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💜 PROLOG

This manual page is part of the POSIX Programmer's Manual. Heads up tho: the Linux implementation of this interface may differ (go check the corresponding Linux manual page for the tea on Linux behavior), or honestly the interface may not even be implemented on Linux. so like. vibe check your platform first 💅

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🎀 NAME

expm1, expm1f, expm1l — compute exponential functions

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🌸 SYNOPSIS

#include <math.h>

double expm1(double x);
float expm1f(float x);
long double expm1l(long double x);

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🦋 DESCRIPTION

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, fr. This volume of POSIX.1‐2017 defers to the ISO C standard. periodt.

These functions shall compute e^x-1.0. that's it, that's the whole job.

An application wishing to check for error situations should set errno to zero and call feclearexcept(FE_ALL_EXCEPT) before calling these functions. On return, if errno is non-zero or fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an error has occurred. like a lil pre-flight checklist, bestie ✈️✨

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👑 RETURN VALUE

Upon successful completion, these functions return e^x-1.0. slay.

• If the correct value would cause overflow, a range error shall occur and expm1(), expm1f(), and expm1l() shall return the value of the macro HUGE_VAL, HUGE_VALF, and HUGE_VALL, respectively. 😭
• If x is NaN, a NaN shall be returned.
• If x is ±0, ±0 shall be returned.
• If x is -Inf, -1 shall be returned.
• If x is +Inf, x shall be returned.
• If x is subnormal, a range error may occur and x should be returned.
• If x is not returned, expm1(), expm1f(), and expm1l() 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:

• Range Error — The result overflows.
  • 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 overflow 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. (translation: the stuff below is bonus content, not requirements 💖)

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🌈 EXAMPLES

None. literally nothing. the examples section is giving minimalist, empty, unbothered. 🙈

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🍓 APPLICATION USAGE

The value of expm1(x) may be more accurate than exp(x)-1.0 for small values of x. that's the whole reason this function exists bestie, don't do subtraction yourself when x is tiny, it's giving catastrophic cancellation 💅

The expm1() and log1p() functions are useful for financial calculations of ((1+x)ⁿ-1)/x, namely:

expm1(n * log1p(x))/x

when x is very small (for example, when calculating small daily interest rates). These functions also simplify writing accurate inverse hyperbolic functions. money math + math math, iconic ✨

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. no cap.

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🧚 RATIONALE

None.

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⭐ FUTURE DIRECTIONS

None.

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💜 SEE ALSO

exp(), feclearexcept(), fetestexcept(), ilogb(), log1p()

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, page EXPM1(3P) — mwah, go forth and compute e^x-1.0 accurately, ily 🎀✨🦋