FDIM(3POSIX)

💖 fdim, fdimf, fdiml — the positive-difference girlies 💖

okay bestie, so this one is from the POSIX Programmer's Manual (yes, that's the manual name, it's giving official). heads up tho, real talk:

⚠️ 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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✨ PROLOG ✨

so like. this page is part of the POSIX Programmer's Manual, periodt. 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. no cap, go check the Linux one if that's your vibe 💅

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🎀 NAME 🎀

fdim, fdimf, fdiml — compute positive difference between two floating-point numbers

like... that's the whole gig. she computes the positive difference between two floating-point numbers. iconic behaviour honestly.

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🌸 SYNOPSIS 🌸

#include <math.h>

double fdim(double x, double y);
float fdimf(float x, float y);
long double fdiml(long double x, long double y);

three sisters, three types, one job. we love a consistent family 🫶

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🦋 DESCRIPTION 🦋

so first things first — 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.1‐2017 defers to the ISO C standard. we're not trying to start drama with ISO C, we're just the messenger ✨

These functions shall determine the positive difference between their arguments:

• if x is greater than y, x-y is returned 🎉
• if x is less than or equal to y, +0 is returned (yeah, zero, she said what she said)

and okay, if you're the kind of app that wants to actually check for error situations (respect), do this: 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, an error has occurred. boom, you got your vibe check 🌈

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👑 RETURN VALUE 👑

Upon successful completion, these functions shall return the positive difference value. slay.

If x-y is positive and overflows, a range error shall occur and fdim(), fdimf(), and fdiml() shall return the value of the macro HUGE_VAL, HUGE_VALF, and HUGE_VALL, respectively. yes, in that order, matching those three functions, don't mix them up 💀

If the correct value would cause underflow, a range error may occur, and fdim(), fdimf(), and fdiml() shall return the correct value, or (if the IEC 60559 Floating-Point option is not supported) an implementation-defined value no greater in magnitude than DBL_MIN, FLT_MIN, and LDBL_MIN, respectively.

If x or y is NaN, a NaN shall be returned. NaN in, NaN out, the circle of life 🧚

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💜 ERRORS 💜

The fdim() function 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.

The fdim() function may fail if:

• Range Error — The result underflows.
  • 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.

🫶 reminder that the following sections are informative. like, they're cute bonus content, not requirements.

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🌈 EXAMPLES 🌈

None. literally none. she's that self-explanatory bestie 😭✨

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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. they're not a package deal, but you can't have neither. fr fr.

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⭐ RATIONALE ⭐

None.

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🔥 FUTURE DIRECTIONS 🔥

None. she's staying exactly as she is, main character energy 👑

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💅 SEE ALSO 💅

• feclearexcept()
• fetestexcept()
• fmax()
• fmin()
• 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, dated 2017, and yeah the page itself is literally called FDIM(3POSIX) — we love a consistent brand. k bye, go compute some positive differences 🦋✨🎀