linux-kernel - RE: [PATCH 2/2] infiniband: Use unsigned for bit index

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Date:	Mon, 2 Feb 2015 12:03:31 +0000
From:	Selvin Xavier <Selvin.Xavier@...lex.Com>
To:	Rasmus Villemoes <linux@...musvillemoes.dk>,
	Roland Dreier <roland@...nel.org>,
	Sean Hefty <sean.hefty@...el.com>,
	Hal Rosenstock <hal.rosenstock@...il.com>
CC:	"linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 2/2] infiniband: Use unsigned for bit index

Acked-by: Selvin Xavier <selvin.xavier@...lex.com>

Thanks!

> -----Original Message-----
> From: linux-rdma-owner@...r.kernel.org [mailto:linux-rdma-
> owner@...r.kernel.org] On Behalf Of Rasmus Villemoes
> Sent: Friday, January 16, 2015 8:10 PM
> To: Roland Dreier; Sean Hefty; Hal Rosenstock
> Cc: Rasmus Villemoes; linux-rdma@...r.kernel.org; linux-
> kernel@...r.kernel.org
> Subject: [PATCH 2/2] infiniband: Use unsigned for bit index
> 
> In the expressions idx/32 and idx%32, both idx and 32 have signed type, and
> unfortunately the C standard prescribes rounding to 0, so unless gcc can
> prove that idx is non-negative, these cannot be implemented as simple shift
> respectively mask operations. Help gcc by changing the type of idx to
> unsigned - this cuts another few instructions from the generated code.
> 
> Signed-off-by: Rasmus Villemoes <linux@...musvillemoes.dk>
> ---
>  drivers/infiniband/hw/ocrdma/ocrdma_verbs.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/infiniband/hw/ocrdma/ocrdma_verbs.c
> b/drivers/infiniband/hw/ocrdma/ocrdma_verbs.c
> index eff11e6c6183..61c3047f5170 100644
> --- a/drivers/infiniband/hw/ocrdma/ocrdma_verbs.c
> +++ b/drivers/infiniband/hw/ocrdma/ocrdma_verbs.c
> @@ -1479,10 +1479,10 @@ mbx_err:
>  	return status;
>  }
> 
> -static void ocrdma_srq_toggle_bit(struct ocrdma_srq *srq, int idx)
> +static void ocrdma_srq_toggle_bit(struct ocrdma_srq *srq, unsigned int
> +idx)
>  {
> -	int i = idx / 32;
> -	unsigned int mask = (1 << (idx % 32));
> +	unsigned int i = idx / 32;
> +	u32 mask = (1U << (idx % 32));
> 
>  	srq->idx_bit_fields[i] ^= mask;
>  }
> --
> 2.1.3
> 
> --
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