[Qemu-devel] Re: [PATCH] Correct use of ! and &

[Aurelien Jarno]

On Fri, Jan 14, 2011 at 10:05:11PM +0000, Blue Swirl wrote:
> Combining bitwise AND and logical NOT is suspicious.
> 
> Fixed by this Coccinelle script:
> // From http://article.gmane.org/gmane.linux.kernel/646367
> @@ expression E1,E2; @@
> (
>   !E1 & !E2
> |
> - !E1 & E2
> + !(E1 & E2)
> )
> 
> Signed-off-by: Blue Swirl <address@hidden>
> ---
>  target-sh4/helper.c |    4 ++--
>  1 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/target-sh4/helper.c b/target-sh4/helper.c
> index 2343366..c6af959 100644
> --- a/target-sh4/helper.c
> +++ b/target-sh4/helper.c
> @@ -380,7 +380,7 @@ static int get_mmu_address(CPUState * env,
> target_ulong * physical,
>                      MMU_DTLB_VIOLATION_READ;
>              } else if ((rw == 1) && !(matching->pr & 1)) {
>                  n = MMU_DTLB_VIOLATION_WRITE;
> -            } else if ((rw == 1) & !matching->d) {
> +            } else if (!(matching->d & (rw == 1))) {

Here, we really want to do a logical comparison, so && is probably
better. Note however that matching->d is a single bit so the code is
doing what it is supposed to do.

>                  n = MMU_DTLB_INITIAL_WRITE;
>              } else {
>                  *prot = PAGE_READ;
> @@ -430,7 +430,7 @@ static int get_physical_address(CPUState * env,
> target_ulong * physical,
>      }
> 
>      /* If MMU is disabled, return the corresponding physical page */
> -    if (!env->mmucr & MMUCR_AT) {
> +    if (!(env->mmucr & MMUCR_AT)) {
>       *physical = address & 0x1FFFFFFF;
>       *prot = PAGE_READ | PAGE_WRITE | PAGE_EXEC;
>       return MMU_OK;

This one is correct.

Thanks for spotting these issues.

-- 
Aurelien Jarno                          GPG: 1024D/F1BCDB73
address@hidden                 http://www.aurel32.net