swap_words_64(9)

💅 swap_words_64 — like, the manual page, bestie

okay so you found swap_words_64(9) in the Kernel API Manual and you're like "what is this" — don't worry, I got you. sit down, hydrate, let's go 🫶

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✨ NAME ✨

swap_words_64 — swap two elements in 64-bit chunks 💫 (yes that's literally it, and yes it's iconic)

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🎀 SYNOPSIS 🎀

void swap_words_64 (void *a , void *b , size_t n );

like, that's the whole vibe. three args, no return, in and out. slay 💅

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🌸 ARGUMENTS 🌸

• a — pointer to the first element to swap 🥇 like, the first one of the two things we're trading
• b — pointer to the second element to swap 🥈 and here's the other one
• n — element size, and it must be a multiple of 8 ⚠️ no cap, fr fr, if it's not a multiple of 8 that's a you problem

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🦋 DESCRIPTION 🦋

okay so what it does: it exchanges the two objects in memory 🔁 that's the whole thing. and the way it does it is genuinely clever — it exploits base+index addressing, which basically all CPUs have, to minimize loop overhead computations. like, the CPU already knows how to do this, so let's not make it do extra math, periodt ✨

we'd like to use 64-bit loads if possible, obviously, main character energy. but if they're not available, emulating one requires base+index+4 addressing, which x86 has but most other processors do not 💀 so that's a whole thing.

if CONFIG_64BIT is set, we definitely have 64-bit loads 🔥 but — and this is the fun part — it's possible to have 64-bit loads without 64-bit pointers (e.g. the x32 ABI 👀). and then the manpage just. asks. out loud:

Are there any cases the kernel needs to worry about? 🤔

like it's literally posing the question in the documentation. no answer. just vibes and an open question. honestly? iconic. iykyk 🌈

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🔥 SEE ALSO 🔥

• Kernel file ./lib/sort.c 🍓
• is_aligned(9)
• swap_words_32(9)
• swap_bytes(9)
• parent(9)
• sort_r(9)
• sort_r_nonatomic(9)

go read those too, bestie, they're all in the family 💜

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ok so that's the page!! it's from the Kernel API Manual, lives in ./lib, and the date on it is October 2026 🌸 mwah, go forth and swap your words in 64-bit chunks, you absolute legend 👑💖