MODF(3POSIX)

✨ MODF(3POSIX) — the POSIX Programmer's Manual ✨

okay bestie, quick heads up before we dive in 💖 this one's from the POSIX Programmer's Manual, and lowkey the Linux version of this interface might do its own thing (so like, go check the matching Linux manual page for the deets on Linux behavior), or honestly it might just not be implemented on Linux at all. no cap. 🙈

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🫶 PROLOG 🫶

so yeah, as I just said: 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 👑

modf, modff, modfl — decompose a floating-point number

like, we're taking a float apart. it's giving surgeon. 💅

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🌸 SYNOPSIS 🌸

#include <math.h>

double modf(double x, double *iptr);
float modff(float value, float *iptr);
long double modfl(long double value, long double *iptr);

yes bestie, modf really does name its first param x while the other two name theirs value. that's just how it is. we don't fix it, we respect it. 🎀

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

okay so here's the actual vibe: these functions shall break the argument x into integral and fractional parts, and each of those parts has the same sign as the argument. periodt.

Then it stores the integral part — as a double (for the modf() function), a float (for the modff() function), or a long double (for the modfl() function) — in the object pointed to by iptr.

so like, the whole-number chunk goes into *iptr, and the leftover crumbs get returned to you. iconic division of labor. ✨

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💖 RETURN VALUE 💖

Upon successful completion, these functions shall return the signed fractional part of x. slay.

• If x is NaN, a NaN shall be returned, and *iptr shall be set to a NaN. (nan everywhere, we're matching 🫶)
• If x is ±Inf, ±0 shall be returned, and *iptr shall be set to ±Inf.

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💀 ERRORS 💀

No errors are defined.

The following sections are informative.

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🌈 EXAMPLES 🌈

None.

ngl, they left us with nothing here. it's giving "figure it out yourself." 😭

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🍓 APPLICATION USAGE 🍓

The modf() function computes the function result and *iptr such that:

a = modf(x, iptr) ;
x == a+*iptr ;

allowing for the usual floating-point inaccuracies.

so like, if you add the return value and *iptr back together, you should get your original x back — allowing for the usual floating-point inaccuracies, because floats are chaotic little creatures and we love them anyway. 💜

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🧚 RATIONALE 🧚

None.

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⭐ FUTURE DIRECTIONS ⭐

None.

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🔥 SEE ALSO 🔥

• frexp()
• isnan()
• ldexp()

The Base Definitions volume of POSIX.1‐2017, <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, mwah 💋 this edition dropped in 2017 courtesy of IEEE/The Open Group (they're the ones behind MODF(3POSIX)), so go forth and decompose some floats responsibly. 🫶🌸