Re: [PATCHv4 5/8] lib: add rocksoft model crc64

[Keith Busch]

On Fri, Mar 04, 2022 at 07:53:44AM +0000, David Laight wrote:
> 
> That can be speeded up by using the identity:
> 	table[x ^ y] == table[x] ^ table[y]
> 
> something like:
> 	crc = poly;  /* actually crc(1) */
> 	table[0] = 0;
> 	table[1] = crc;
> 	for (i = 2; i < 8; i++) [
> 		crc = crc & 1 ? (crc >> 1) ^ poly : crc >> 1;
> 		for (j = 0; j < 1u << i; j++)
> 			table[j + (1i << i)] = table[j] ^ crc;
> 	}
> 
> I think the same code can be used for a normal MSB first crc
> provided both the polynomial and crc(1) are passed in.
> 
> OTOH initialisation speed may not matter.

I don't think speed is an issue here. This part is executed just once
for the initial kernel compile, then never again.