__ffs64(9)

🌈 __ffs64 🌈

okay so bestie, welcome to the Kernel API Manual page for __ffs64 💅 she finds the first set bit in a 64 bit word, and honestly? iconic.

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🎀 NAME 🎀

__ffs64 — find first set bit in a 64 bit word ✨

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🦋 SYNOPSIS 🦋

unsigned int __ffs64 (u64 word );

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🍓 ARGUMENTS 🍓

• word — the 64 bit word. that's the value you're handing over, bestie 🫶

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💖 DESCRIPTION 💖

On 64 bit arches this is a synonym for __ffs.

Real talk though: the result is not defined if no bits are set 😭 so check that word is non-zero before calling this. like, do the vibe check first, fr fr.

no cap: if you skip that check, the result is not defined — so please don't come crying to me.

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👑 SEE ALSO 👑

Kernel file ./include/linux/bitops.h is in the group chat, along with the whole squad:

• rol64(9)
• ror64(9)
• rol32(9)
• ror32(9)
• rol16(9)
• ror16(9)
• rol8(9)
• ror8(9)
• sign_extend32(9)
• sign_extend64(9)
• get_count_order_long(9)
• parity8(9)
• fns(9)
• assign_bit(9)
• __ptr_set_bit(9)
• __ptr_clear_bit(9)
• __ptr_test_bit(9)

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mwah 💖 source/version: ./include/linux, dated October 2026. __ffs64(9) out. periodt. 🧚‍♀️