Messages in this thread | | | Date | Tue, 9 Jul 2013 13:17:45 +0530 | From | Vineet Gupta <> | Subject | Re: [PATCH] lib: One less subtraction in binary search iterations. |
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On 07/09/2013 09:21 AM, Wedson Almeida Filho wrote: > On Sat, Jul 6, 2013 at 9:59 PM, Joe Perches <joe@perches.com> wrote: >> >> Not correct. >> >>> while (start < end) { >>> - size_t mid = start + (end - start) / 2; >>> + size_t mid = (start + end) / 2; >> >> size_t start = 0x80000000; >> size_t end = 0x80000001; > > Good point, they aren't equivalent in all cases. > > For the overflow to happen though, we need an array with at least > N/2+1 entries, where N is the address space size. The array wouldn't > fit in addressable memory if the element size is greater than 1, so > this can only really happen when the element size is 1. Even then, it > would require the kernel range to be greater than half of all > addressable memory, and allow an allocation taking that much memory. I > don't know all architectures where linux runs, but I don't think such > configuration is likely to exist. >
It does. In ARC port (arch/arc), the untranslated address space starts at 0x8000_0000 and this is where kernel is linked at. So all ARC kernel addresses (code/data) lie in that range. This means you don't need special corner case for this trip on ARC - it will break rightaway - unless I'm missing something.
P.S. Sorry for not replying earlier than ur v2.
-Vineet
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