STDC_FIRST_LEADING_ZERO(3)

💅 STDC_FIRST_LEADING_ZERO(3) — find the first leading zero in an integer

okay bestie, so this one lives in the Standard C Library — that's libc, link it with -lc — and it's all about finding that first lil zero hiding at the front of your integer. let's get into it 🎀

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✨ SYNOPSIS ✨

first things first, you gotta invite the header:

#include <stdbit.h>

and here's the whole squad, all of them returning unsigned int:

unsigned int
stdc_first_leading_zero_uc(unsigned char value);

unsigned int
stdc_first_leading_zero_us(unsigned short value);

unsigned int
stdc_first_leading_zero_ui(unsigned int value);

unsigned int
stdc_first_leading_zero_ul(unsigned long value);

unsigned int
stdc_first_leading_zero_ull(unsigned long long value);

unsigned int
stdc_first_leading_zero(value);

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🦋 DESCRIPTION 🦋

so the stdc_first_leading_zero_type() family (yes, _type is the placeholder, keep up 😌) hands you back the index of the most significant clear bit in value. and value can be any of these:

• unsigned char → that's uc
• unsigned short → that's us
• unsigned int → that's ui
• unsigned long → that's ul
• unsigned long long → that's ull

match them up respectively, iykyk 💫

and then there's stdc_first_leading_zero(value) — the type-generic macro — which is the main character here fr. it looks at whatever type value actually is and picks the right stdc_first_leading_zero_type() function for you. no cap, it just knows. 👑

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🔥 RETURN VALUES 🔥

it returns the index of the most significant clear bit in value. and the numbering? listen closely bestie:

• the most significant bit is number 1
• the least significant bit is number w, where w is the number of bits in the type of value

and here's the little plot twist 🙈 — if there are no clear bits in value at all (like, value is the bitwise complement of zero), it returns zero. that's your "nothing to see here" signal. 💀

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🌈 SEE ALSO 🌈

go read these next, they're literally the friend group:

• stdbit(3)
• stdc_leading_ones(3)
• stdc_first_leading_ones(3)
• stdc_first_trailing_zero(3)

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⭐ STANDARDS ⭐

the stdc_first_leading_zero_type() family of functions and the stdc_first_leading_zero() type-generic macro conform to .

ok so the standard name is literally blank in the source page 🫠 not me pointing it out, but yeah, that's the whole line. keeping it 100% as-is.

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🧚 HISTORY 🧚

the stdc_first_leading_zero_type() family of functions and the stdc_first_leading_zero() type-generic macro were added in FreeBSD 15.1. fresh out the oven, periodt. ✨

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👑 AUTHOR 👑

Robert Clausecker <fuz@FreeBSD.org> — ty for your service bestie 🫶

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so yeah, that's the page!! this one's from Debian, dated November 9, 2025 — go find your leading zeros, slay, and remember: bit 1 is the most significant one, don't embarrass yourself 💅🌸