log2(3)

✨ log2(3) ✨

okay so bestie, welcome to the log2 page of the Linux man-pages (that's the Library Functions Manual btw 💜). this is the lowdown on the base-2 logarithm crew and honestly? they ate. let's get into it 💅

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🌸 NAME 🌸

log2, log2f, log2l — the base-2 logarithmic function, aka the whole girl group 🎀

📚 LIBRARY 📚

the Math library — link it with libm, so like -lm when you're compiling. don't forget it or she will NOT show up. periodt 💀

🦋 SYNOPSIS 🦋

#include <math.h>

double log2(double x);
float log2f(float x);
long double log2l(long double x);

🔍 Feature Test Macro Requirements for glibc (see feature_test_macros(7)): 🔍

log2(), log2f(), log2l():

_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L

no cap, you gotta have one of those defined or glibc's like "who r u" 🙈

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💖 DESCRIPTION 💖

these functions return the base-2 logarithm of x. that's the whole personality trait. simple, iconic, no notes ✨

👑 RETURN VALUE 👑

on success, these functions return the base-2 logarithm of x. slay.

for special cases — and bestie that includes when x is 0, 1, negative, infinity, or NaN — you gotta go see log(3). she's got the tea ☕

😭 ERRORS 😭

peep math_error(7) for the info on how to figure out whether an error has even occurred when you call these functions. detection era 🔎

and for the full discussion of the errors that can occur for these functions? yeah, again, go read log(3). she spilled first 💅

🧚 ATTRIBUTES 🧚

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

• log2(), log2f(), log2l() — Thread safety: MT-Safe 🫶

(that's the whole table bestie, just the one row, and she's MT-Safe so you can vibe in multiple threads no problem 💜)

🌈 STANDARDS 🌈

C11, POSIX.1-2008. certified, official, main character energy 👑

📜 HISTORY 📜

glibc 2.1. C99, POSIX.1-2001. look at her, ancient icon, still serving 🎀

the variant returning double also conforms to SVr4 and 4.3BSD. so she's versatile too?? obsessed 🔥

🍓 SEE ALSO 🍓

• cbrt(3)
• clog2(3)
• log(3)
• log10(3)
• sqrt(3)

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ngl if you're out here passing a negative or a zero to these, that's undefined-ish behaviour territory — go read log(3) before you're shocked pikachu 😭 the whole special-case saga lives there.

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and that's the page bestie!! this came straight from Linux man-pages 6.20, dated 2026-02-08, all about our girl log2(3). go forth and compute some base-2 logs, you absolute icon 🫶✨💖