[PATCH RFC v3 2/9] virtio_net: Add functions for hashing

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



> +
> +static inline void virtio_net_toeplitz(struct virtio_net_toeplitz_state *state,
> +				       const __be32 *input, size_t len)
> 
> The function calculates a hash value but its name does not make it
> clear. Consider adding a 'calc'.
> 
> +{
> +	u32 key;
> +
> +	while (len) {
> +		state->key++;
> +		key = be32_to_cpu(*state->key);
> 
> You perform be32_to_cpu to support both CPU endianities.
> If you will follow with an unconditional swab32, you could run the
> following loop on a more natural 0 to 31 always referring to bit 0
> and avoiding !!(key & bit):
> 
> key = swab32(be32_to_cpu(*state->key));
> for (i = 0; i < 32; i++, key >>= 1) {
> 	if (be32_to_cpu(*input) & 1)
> 		state->hash ^= state->key_buffer;
> 	state->key_buffer = (state->key_buffer << 1) | (key & 1);
> }
> 

Fixing myself, in previous version 'input' was tested against same bit.
Advantage is less clear now, replacing !! with extra shift.
However, since little endian CPUs are more common, the combination of
swab32(be32_to_cpu(x) will actually become a nop.
Similar tactic may be applied to 'input' by assigning it to local
variable. This may produce more efficient version but not necessary
easier to understand.

key = bswap32(be32_to_cpu(*state->key));
for (u32 bit = BIT(31); bit; bit >>= 1, key >>= 1) {
	if (be32_to_cpu(*input) & bit)
		state->hash ^= state->key_buffer;
	state->key_buffer =
		(state->key_buffer << 1) | (key & 1);
}

> 
> +
> +		for (u32 bit = BIT(31); bit; bit >>= 1) {
> +			if (be32_to_cpu(*input) & bit)
> +				state->hash ^= state->key_buffer;
> +
> +			state->key_buffer =
> +				(state->key_buffer << 1) | !!(key & bit);
> +		}
> +
> +		input++;
> +		len--;
> +	}
> +}
> +




[Index of Archives]     [KVM Development]     [Libvirt Development]     [Libvirt Users]     [CentOS Virtualization]     [Netdev]     [Ethernet Bridging]     [Linux Wireless]     [Kernel Newbies]     [Security]     [Linux for Hams]     [Netfilter]     [Bugtraq]     [Yosemite Forum]     [MIPS Linux]     [ARM Linux]     [Linux RAID]     [Linux Admin]     [Samba]

  Powered by Linux