effhash(9)

💅 effhash(9) — Kernel API Manual 🎀

okay bestie, welcome to effhash(9) — yes, the manual name is effhash and the manual section is 9 (that's the kernel-API section, iykyk). we're gonna get into it.

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✨ NAME ✨

effhash — a hash function made specifically for 29 bit CAN identifier reduction 🚗💨

fr fr that's the whole job. that's what she does.

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🌸 SYNOPSIS 🌸

unsigned int effhash (canid_t can_id );

like, that's it. so clean. so iconic. 🫶

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🦋 ARGUMENTS 🦋

• can_id — a 29 bit CAN identifier ⭐

that's the one and only thing you hand her.

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🧚 DESCRIPTION 🧚

okay so here's the situation, and honestly? it's giving optimization arc.

there's this one linked list of single EFF CAN frame subscriptions, right, and walking that thing linearly was lowkey a lot. so the move is: map that whole 29 bit identifier down to 10 bits. ten bits. tiny. adorable. manageable. 🎀

literally all she's doing is squishing the id down so the lookup doesn't have to trawl through the whole list like it's scrolling forever.

bestie, this bit-width situation is defined in the CAN_EFF_RCV_HASH_BITS definition — go say hi to it if you want the details 👀

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🔥 RETURN 🔥

the hash value, ranging from 0x000 – 0x3FF 💖

and ngl, that range is enforced by the CAN_EFF_RCV_HASH_BITS mask — so don't go expecting her to hand you back anything outside it, because she won't. no cap. 🙈

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🌈 SEE ALSO 🌈

• Kernel file ./net/can/af_can.c 📁
• can_send(9)
• can_rcv_list_find(9)
• can_rx_register(9)
• can_rx_unregister(9)
• can_proto_register(9)
• can_proto_unregister(9)

go read those too, they're all part of the same little friend group 💜

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and that's the whole page, bestie! this one came out of the ./net/can directory, dated October 2026, and it's registered as effhash(9). slay, go hash responsibly 💅✨