link_crc.h File Reference

CRC-16 (cyclic redundancy check): polynomial 0x1021, no reflection, no final XOR, seed passed by the caller. More...

#include <stddef.h>
#include <stdint.h>

Go to the source code of this file.

Macros
#define	LINK_CRC_INIT   0xFFFFu
	The value a fresh accumulator starts at.
#define	LINK_CRC_CHECK   0x29B1u
	The published check value: link_crc(LINK_CRC_INIT, "123456789", 9).
#define	LINK_FNV_INIT   0x811C9DC5uL
	The FNV-1a (Fowler-Noll-Vo) 32-bit offset basis, a fresh accumulator.
#define	LINK_FNV_CHECK   0xBB86B11CuL
	The published check value: link_fnv1a32(LINK_FNV_INIT, "123456789", 9).

Functions
uint16_t	link_crc (uint16_t crc, const void *data, size_t len)
	Fold len bytes into crc and return the new accumulator.
uint32_t	link_fnv1a32 (uint32_t hash, const void *data, size_t len)
	FNV-1a, 32 bits: per byte, XOR then multiply by 16777619.

Detailed Description

CRC-16 (cyclic redundancy check): polynomial 0x1021, no reflection, no final XOR, seed passed by the caller.

With the seed 0xFFFF this is CRC-16/CCITT-FALSE, whose published check value is 0x29B1 over the ASCII string "123456789". With the seed 0x0000 it is CRC-16/XMODEM, which the OpenYGE protocol uses (check value 0x31C3); protocols/openyge carries its own routine and does not call this one.

The panel link carries no CRC of its own: CAN (Controller Area Network) provides a 15-bit CRC, an acknowledge slot and retransmission in silicon.

SPDX-License-Identifier: MIT

Function Documentation

link_crc()

uint16_t link_crc	(	uint16_t	crc,
		const void *	data,
		size_t	len )

Fold len bytes into crc and return the new accumulator.

Incremental, so a receiver can check a frame as it arrives without buffering it first.

Parameters

crc	The accumulator: LINK_CRC_INIT, or the value a previous call returned.
data	The bytes to fold in.
len	Number of bytes in data.

Returns

The new accumulator.

link_fnv1a32()

uint32_t link_fnv1a32	(	uint32_t	hash,
		const void *	data,
		size_t	len )

FNV-1a, 32 bits: per byte, XOR then multiply by 16777619.

The content key of the board drawing (LINK_AW_HASH_LO/HI) next to its CRC. Not a cryptographic hash; it tells two drawings apart, it does not authenticate one. Incremental like link_crc().

Parameters

hash	The hash: LINK_FNV_INIT, or the value a previous call returned.
data	The bytes to fold in.
len	Number of bytes in data.

Returns

The new hash.