asin(3)

✨ asin(3) — the arc sine bestie ✨

okay so real talk, this is asin from section 3 of the Linux man-pages, aka the arc sine function, and it's about to be your new fave trig girlie, no cap 💖

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💖 NAME 💖

asin, asinf, asinl — arc sine function, periodt ✨

📚 LIBRARY 📚

Math library (libm, link it with -lm) 🧮

bestie if you forget the -lm the linker WILL humble you, iykyk 😭

🌸 SYNOPSIS 🌸

#include <math.h>

double asin(double x);
float asinf(float x);
long double asinl(long double x);

🦋 Feature Test Macro Requirements for glibc (see feature_test_macros(7)) 🦋

like, if you want asinf() and asinl() to even exist, you gotta define these, bestie:

asinf(), asinl():
    _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
        || /* Since glibc 2.19: */ _DEFAULT_SOURCE
        || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

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👑 DESCRIPTION 👑

So these functions calculate the principal value of the arc sine of x — which is literally just "the value whose sine is x". It's giving undo-button for sin(), fr fr 💅

🌈 RETURN VALUE 🌈

okay so on success, these functions return the principal value of the arc sine of x in radians, and the return value lives in the range [-pi/2, pi/2]. iconic range, no notes 💖

• If x is a NaN, a NaN is returned. (NaN in, NaN out, the vibes stay consistent 🫶)
• If x is +0 (-0), +0 (-0) is returned. (it just hands your zero right back to you, respectfully ✨)
• If x is outside the range [-1, 1], a domain error occurs, and a NaN is returned. yeah she's not doing that one 😭

💀 ERRORS 💀

go read math_error(7) if you wanna know how to tell whether an error actually happened when you called these functions ✨

The following errors can occur:

• Domain error: x is outside the range [-1, 1] — errno is set to EDOM, and an invalid floating-point exception (FE_INVALID) is raised. ma'am that input is simply not invited 🚫

🎀 ATTRIBUTES 🎀

for an explanation of the terms used in this section, see attributes(7) 💜

• Interface: asin(), asinf(), asinl() — Attribute: Thread safety — Value: MT-Safe 👑

thread safety slay!! she's safe to share with all your little threads, bestie 🧚

⭐ STANDARDS ⭐

C11, POSIX.1-2008. certified and everything ✨

📜 HISTORY 📜

C99, POSIX.1-2001. she's been around, and she's been thriving 💅

The variant returning double also conforms to SVr4, 4.3BSD, C89. (the double girlie has the longest résumé, we love a versatile icon 👑)

🌸 SEE ALSO 🌸

acos(3), atan(3), atan2(3), casin(3), cos(3), sin(3), tan(3) — the whole trig friend group, go say hi 🫶

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and that's the whole page bestie!! this was Linux man-pages 6.20, dated 2026-02-08, filed as asin(3) — mwah, go compute some arcs 💖✨🌙