Re: [PATCH 1/8] lib/sort: Heapsort implementation of sort()

[Andreas Gruenbacher]

On Wed, 2005-02-02 at 11:50, Herbert Xu wrote:
> Andreas Gruenbacher <agruen@xxxxxxx> wrote:
> > 
> > static inline void swap(void *a, void *b, int size)
> > {
> >        if (size % sizeof(long)) {
> >                char t;
> >                do {
> >                        t = *(char *)a;
> >                        *(char *)a++ = *(char *)b;
> >                        *(char *)b++ = t;
> >                } while (--size > 0);
> >        } else {
> >                long t;
> >                do {
> >                        t = *(long *)a;
> >                        *(long *)a = *(long *)b;
> >                        *(long *)b = t;
> >                        size -= sizeof(long);
> >                } while (size > sizeof(long));
> >        }
> > }
> 
> What if a/b aren't aligned?

That would be the case if the entire array was unaligned, or (size %
sizeof(long)) != 0. If people sort arrays that are unaligned even though
the element size is a multiple of sizeof(long) (or sizeof(u32) as Matt
proposes), they are just begging for bad performance. Otherwise, we're
doing byte-wise swap anyway.

-- 
Andreas Gruenbacher <agruen@xxxxxxx>
SUSE Labs, SUSE LINUX GMBH

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