scalbln(3)

💖 scalbln(3) 💖

okay so bestie, welcome to the scalbln(3) page from the Library Functions Manual — yes she's a real one, she lives in the math library, and she is here to scale your numbers by an integer power of radix. slay. let's get into it 💅

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✨ NAME ✨

scalbn, scalbnf, scalbnl, scalbln, scalblnf, scalblnl — scale by an integer power of radix 🎀

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📚 LIBRARY 📚

Math library (libm, -lm). yeah you gotta link her. don't forget -lm or she Will Not Show Up. 😭

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🌸 SYNOPSIS 🌸

#include <math.h>

double scalbln(double x, long e);
float scalblnf(float x, long e);
long double scalblnl(long double x, long e);

double scalbn(double x, int e);
float scalbnf(float x, int e);
long double scalbnl(long double x, int e);

🦋 Feature Test Macro Requirements for glibc 🦋

(for the deets, go see feature_test_macros(7) — she explains everything)

scalbln(), scalblnf(), scalblnl():

_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
    || /* Since glibc 2.19: */ _DEFAULT_SOURCE

scalbn(), scalbnf(), scalbnl():

_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 what do these girlies actually do? they take your first argument x and multiply it by FLT_RADIX (which is probably 2, like, statistically) raised to the power of e. that's it. that's the whole vibe:

x * FLT_RADIX ** e

and where does FLT_RADIX come from, you ask? you just #include <float.h> and she's right there. main character energy. ✨

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🫶 RETURN VALUE 🫶

• when everything goes right, you get x * FLT_RADIX ** e. periodt.
• if x is a NaN, a NaN comes back. (NaN in, NaN out, it's giving consistency 💀)
• if x is positive infinity (or negative infinity), you get positive infinity (or negative infinity) right back. she mirrors, she returns.
• if x is +0 (or -0), you get +0 (or -0) back. zero stays zero, iconic.
• if the result overflows, that's a range error, and you get HUGE_VAL, HUGE_VALF, or HUGE_VALL respectively — with the same sign as x. big. HUGE even. 😭
• if the result underflows, also a range error, and you get zero — again, same sign as x.

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🔥 ERRORS 🔥

want to know if something went wrong when you called these? go read math_error(7), she'll walk you through it.

here's what can happen:

• Range error, overflow — an overflow floating-point exception (FE_OVERFLOW) gets raised.
• Range error, underflow — errno gets set to ERANGE, and an underflow floating-point exception (FE_UNDERFLOW) gets raised.

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🌈 ATTRIBUTES 🌈

for what all these terms even mean, check attributes(7) — she's the glossary bestie.

• scalbn(), scalbnf(), scalbnl(), scalbln(), scalblnf(), scalblnl() — Thread safety: MT-Safe 🎉

(yes, all six of them, same row, same fortune. we love a collective slay.)

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⭐ STANDARDS ⭐

C11, POSIX.1-2008. certified, official, no notes. 💅

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🎀 HISTORY 🎀

glibc 2.1. C99, POSIX.1-2001.

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🎀 HISTORY 🎀

(yes there's two HISTORY sections, bestie, the page just has range like that)

so here's the tea: these functions are different from the obsolete ones described over in scalb(3), and the difference is the type of their second argument. the functions on this page have a second argument of an integral type, while the ones in scalb(3) have a second argument of type double. that's the whole distinction. iykyk. 🧚

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💜 NOTES 💜

if FLT_RADIX equals 2 (which is, like, the usual situation), then scalbn() is equivalent to ldexp(3). cute little crossover episode. 🦋

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💀 BUGS 💀

before glibc 2.20, these functions did not set errno for range errors. so if you're on an ancient glibc and you're checking errno... yeah. she wasn't doing that yet. 🙈

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🌟 SEE ALSO 🌟

• ldexp(3)
• scalb(3)

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and that's the whole page, bestie!! so much love to the Linux man-pages 6.20 girlies and their 2026-02-08 drop — go forth and scale responsibly 🫶🌸💖✨