Messages in this thread Patch in this message | | | Date | Fri, 20 Mar 2015 14:28:03 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH] lib/idr.c: remove duplicated bound checking in sub_alloc |
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On Thu, 19 Mar 2015 17:57:07 +0000 Liu Sha <rednoax@qq.com> wrote:
> From: Liu Sha <rednoax@gmail.com> > > The INT_MAX bound checking in sub_alloc checks two conditions to see > whether the signed integer "id" is beyond INT_MAX: > > if ((id >= MAX_IDR_BIT) || (id < 0)) > return -ENOSPC; > > These two conditions are actually the same for "int" variable so one > of them can be removed. If the above snippet is compiled with -Os option > of gcc, only one checking will remain in disassembly code. > > --- a/lib/idr.c > +++ b/lib/idr.c > @@ -262,7 +262,7 @@ static int sub_alloc(struct idr *idp, int *starting_id, struct idr_layer **pa, > sh = IDR_BITS*l; > id = ((id >> sh) ^ n ^ m) << sh; > } > - if ((id >= MAX_IDR_BIT) || (id < 0)) > + if (id >= MAX_IDR_BIT) > return -ENOSPC; > if (l == 0) > break;
Well. This only works because MAX_IDR_BIT happens to have unsigned type, so the comparison is done with unsigned arithmetic.
The patch makes no difference to code size with my gcc and I'm inclined to leave the code as-is for reasons of safety and clarity.
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