netdev - Re: [net-next] be2net: use shift instead of expensive divide

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Date:   Mon, 28 Aug 2017 20:44:02 -0700
From:   Joe Perches <joe@...ches.com>
To:     Zhang Shengju <zhangshengju@...s.chinamobile.com>,
        sathya.perla@...adcom.com, ajit.khaparde@...adcom.com,
        sriharsha.basavapatna@...adcom.com, netdev@...r.kernel.org
Subject: Re: [net-next] be2net: use shift instead of expensive divide

On Tue, 2017-08-29 at 11:18 +0800, Zhang Shengju wrote:
> Replace shift instead of expensive divide.

This change is mostly pointless.
Any half-way decent compiler should produce the same object.
gcc emits the same object with the old code.

The AMAP_GET_BITS macro uses the "offsetof(struct, member) / 32"
style too.

> diff --git a/drivers/net/ethernet/emulex/benet/be_main.c b/drivers/net/ethernet/emulex/benet/be_main.c
[]
> @@ -2455,7 +2455,7 @@ static struct be_rx_compl_info *be_rx_compl_get(struct be_rx_obj *rxo)
>  
>  	/* For checking the valid bit it is Ok to use either definition as the
>  	 * valid bit is at the same position in both v0 and v1 Rx compl */
> -	if (compl->dw[offsetof(struct amap_eth_rx_compl_v1, valid) / 32] == 0)
> +	if (compl->dw[offsetof(struct amap_eth_rx_compl_v1, valid) >> 5] == 0)

etc...