On Mon, 22 Oct 2007 12:36:19 -0700
Joe Perches <[EMAIL PROTECTED]> wrote:
> It's a bit after 2.6.1 now...
>
> Removes unnecessary if, uses 16 bit rotate left.
> Performance improves ~30%
>
> Signed-off-by: Joe Perches <[EMAIL PROTECTED]>
>
> diff --git a/net/appletalk/ddp.c b/net/appletalk/ddp.c
> index 7c0b515..1c50f4c 100644
> --- a/net/appletalk/ddp.c
> +++ b/net/appletalk/ddp.c
> @@ -925,15 +925,9 @@ static int atrtr_ioctl(unsigned int cmd, void __user
> *arg)
> static unsigned long atalk_sum_partial(const unsigned char *data,
> int len, unsigned long sum)
> {
> - /* This ought to be unwrapped neatly. I'll trust gcc for now */
> while (len--) {
> - sum += *data;
> - sum <<= 1;
> - if (sum & 0x10000) {
> - sum++;
> - sum &= 0xffff;
> - }
> - data++;
> + sum += *data++;
> + sum = ((sum & 0x8000)>>15) | ((sum & 0x7fff)<<1);
> }
> return sum;
> }
>
The end of the message you quoted was:
> Corrected fast code is:
>
> while (len--) {
> sum += *data++;
> sum <<= 1;
> sum = (((sum & 0x10000) >> 16) + sum) & 0xffff;
> }
>
> At least it is correct on the standalone random data test, and the
> new code is 30% faster for the cached memory case (13.7 clks/byte vs 18
> clks/byte).
Your code looks different...
--
Stephen Hemminger <[EMAIL PROTECTED]>
-
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to [EMAIL PROTECTED]
More majordomo info at http://vger.kernel.org/majordomo-info.html
