LIBMURMURHASH(3)

💖 LIBMURMURHASH — the manual page, but make it slay 💖

okay so bestie, welcome to libmurmurhash(3), straight out of the libmurmurhash manual 📚✨. This is your girl explaining non-cryptographic hash functions to you like we're texting at 2am. Buckle up, it's giving very technical but also very cute. 🎀

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✨ NAME ✨

libmurmurhash — non-cryptographic hash functions 🔥

like... it hashes your bytes, but it is NOT for keeping secrets, okay? Not every hash has to be a bodyguard. 💅

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🌸 SYNOPSIS 🌸

First things first, you gotta include the header, no cap:

#include <murmurhash.h>

Then here are the three icons themselves 👑:

void lmmh_x86_32(const void *addr, unsigned int len, uint32_t seed, uint32_t out[1]);
void lmmh_x86_128(const void *addr, unsigned int len, uint32_t seed, uint32_t out[4]);
void lmmh_x64_128(const void *addr, unsigned int len, uint32_t seed, uint64_t out[2]);

💀 Deprecated API 💀

These ones still exist but they're giving "nostalgia post from 2014". They are deprecated, bestie, don't start anything new with them:

void MurmurHash3_x86_32(const void *data, int len, uint32_t seed, void *out);
void MurmurHash3_x86_128(const void *data, int len, uint32_t seed, void *out);
void MurmurHash3_x64_128(const void *data, int len, uint32_t seed, void *out);

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🦋 DESCRIPTION 🦋

So. LibMurmurHash hands you all three variants of MurmurHash3, taken straight from the original source. No remixes, no edits, the original audio. 🎧

Let's break the params down because the way that each one matters:

• addr — the very first parameter, and it points to where your data starts in memory. The beginning. The main character's entrance. ✨
• len — the second parameter, and it's literally just how many bytes you want hashed. Count them. Be precise. 🔢
• seed — the third parameter, and this one's fun: you can use it to compute a completely different hash over the exact same data. Same bytes, different seed, different vibe. 🎲
• out — and finally you pass the location where the hash should be written. It writes there. That's it. That's the whole thing. 🫶

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🌈 EXAMPLE 🌈

Say you wanna compute the hash of length bytes starting from data, and then print that 32-bit sized hash value. Iconic, let's go:

uint32_t hash;
lmmh_x86_32(data, length, 0, &hash);
printf("%" PRIx32 "", hash);

And now the same thing but wider, because sometimes you want more hash per hash. Bigger. Bolder. 💅

uint64_t widehash[2];
lmmh_x64_128(data, length, 0, widehash);
printf("%" PRIx64 "%" PRIx64 "", widehash[0], widehash[1]);

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👑 AUTHORS 👑

Credit where credit is due, always, fr fr:

• MurmurHash was created by Austin Appleby.
• PMurHash was written by Shane Day.
• libmurmurhash was created by Fabian Klötzl.

And get this — all code is dedicated to the public domain. Free. For everyone. Periodt. 🎀

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😭 BUGS 😭

Okay so the old API is problematic and I need you to hear me on this:

• a negative len stays unchecked 💀 like it will not stop you, it will simply not look
• the output parameter has very specific alignment requirements ⚠️ so line it up correctly or perish
• and on top of all that, the order of bytes in the hash may differ across architectures 🌀 so don't go assuming it looks the same everywhere

Not me warning you about undefined-adjacent chaos in a manpage. But like. I warned you. 🙈

🐛 Reporting Bugs 🐛

Found something? Please file a bug on GitHub at github.com/kloetzl/libmurmurhash or send a mail to fabian-libmurmurhash@kloetzl.info. They wanna hear from you, bestie, don't be shy. 💌

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and that's the whole page, you ate it, you understood it, you're a Unix girlie now 💖✨🦋🌸

This was libmurmurhash, version 1, dated 2019-02-04 — the libmurmurhash manual. Byeeee, go hash something responsibly 🫶💅