On 09/14/2017 03:44 AM, Laszlo Ersek wrote: > On 09/13/17 23:03, Eric Blake wrote: >> When using bit-wise operations that exploit the power-of-two >> nature of the second argument of ROUND_UP(), we still need to >> ensure that the mask is as wide as the first argument (done >> by using addition of 0 to force proper arithmetic promotion). >> Unpatched, ROUND_UP(2ULL*1024*1024*1024*1024, 512) produces 0, >> instead of the intended 2TiB. >> >> Broken since its introduction in commit 292c8e50 (v1.5.0). >> >> CC: qemu-triv...@nongnu.org >> Signed-off-by: Eric Blake <ebl...@redhat.com> >>
>> +#define ROUND_UP(n, d) (((n) + (d) - 1) & -((n) - (n) + (d))) >> #endif > > Another way to widen the mask as necessary would be: > > (((n) + (d) - 1) & -(0 ? (n) : (d))) Oh, I like that even better! >> #ifndef DIV_ROUND_UP >> -#define DIV_ROUND_UP(n,d) (((n) + (d) - 1) / (d)) >> +#define DIV_ROUND_UP(n, d) (((n) + (d) - 1) / (d)) >> #endif > > This looks like an independent whitespace fix; should it be in this patch? checkpatch complained about the pre-patch spacing in ROUND_UP, and DIV_ROUND_UP had the same issue 2 lines later. But you're right that it's not strictly necessary (or that I should at least call it out in the commit message). v2 coming up. -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3266 Virtualization: qemu.org | libvirt.org
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