FABS(3P)

💖 FABS(3P) — POSIX Programmer's Manual 💖

okay bestie, so this is the manual page for fabs, fabsf, and fabsl, and it lives in the POSIX Programmer's Manual (that's the <rainbow>3P</rainbow> in the corner, iykyk). grab a boba, we're doing absolute values ✨

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🎀 PROLOG 🎀

okay so before literally anything else, a lil heads up:

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.

so like. it's the POSIX flavor of the truth. Linux might be doing its own thing. check the Linux page if you're on Linux. or maybe it's just not there. lowkey terrifying but that's the deal 🫶

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💅 NAME 💅

fabs, fabsf, fabsl — the absolute value function. that's it, that's the whole vibe. takes a number, strips the lil minus sign off. iconic behavior, no cap.

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✨ SYNOPSIS ✨

#include <math.h>

double fabs(double x);
float fabsf(float x);
long double fabsl(long double x);

three functions, three flavors of float precision, one job. pick your fighter 💖

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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.

(translation: if this page and the ISO C standard ever beef, ISO C wins. not me picking sides, that's just what it says 🥲)

These functions shall compute the absolute value of their argument x, |x|. so if x is negative, you get the positive version. if it's already positive, it stays. main character energy either way 👑

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🔥 RETURN VALUE 🔥

Upon successful completion, these functions shall return the absolute value of x. slay.

but wait, the edge cases are where it gets spicy:

• If x is NaN, a NaN shall be returned. (NaN in, NaN out. it's giving consistency 💀)
• If x is ±0, +0 shall be returned. (the minus on that zero? gone. not invited.)
• If x is ±Inf, +Inf shall be returned. (negative infinity? never met her, only positive infinity here 💅)

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💜 ERRORS 💜

No errors are defined.

The following sections are informative.

literally cannot fail. it's the unbothered, moisturized, in her lane function of the math library. periodt.

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🦋 EXAMPLES 🦋

🌈 Computing the 1-Norm of a Floating-Point Vector

This example shows the use of fabs() to compute the 1-norm of a vector defined as follows:

norm1(v) = |v[0]| + |v[1]| + ... + |v[n-1]|

where |x| denotes the absolute value of x, n denotes the vector's dimension v[i] denotes the i-th component of v (0≤i<n).

so like, you take every component of the vector, chop off any negative signs, and add them all up. that's the 1-norm bestie, it's a whole thing 🎀

#include <math.h>

double
norm1(const double v[], const int n)
{
    int     i;
    double  n1_v;  /* 1-norm of v */

    n1_v = 0;
    for (i=0; i<n; i++) {
        n1_v += fabs (v[i]);
    }

    return n1_v;
}

see how fabs is doing the heavy lifting inside the loop? that's the moment. chef's kiss. ate and left no crumbs 🍓

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⭐ APPLICATION USAGE ⭐

None.

(nothing extra to add, it just works ✨)

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💀 RATIONALE 💀

None.

(the committee had zero notes. zero. obsessed with that for them honestly)

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🌟 FUTURE DIRECTIONS 🌟

None.

(no glow-up planned, she's perfect as is 👑)

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🧚 SEE ALSO 🧚

• isnan()
• The Base Definitions volume of POSIX.1‐2017, <math.h>

go read isnan() if you wanna vibe with NaN detection, and <math.h> if you wanna know where all this stuff actually lives 📚

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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 — yeah, 2017, she's vintage, she's timeless, she's still serving 💅✨