Re: [PATCH v3 1/3] riscv: optimized memcpy

[Matteo Croce <mcroce@linux.microsoft.com>]

On Tue, Jun 22, 2021 at 10:19 AM David Laight <David.Laight@aculab.com> wrote:
>
> From: Christoph Hellwig
> > Sent: 21 June 2021 15:27
> ...
> > > +           for (next = s.ulong[0]; count >= bytes_long + mask; count -= bytes_long) {
> >
> > Please avoid the pointlessly overlong line.  And (just as a matter of
> > personal preference) I find for loop that don't actually use a single
> > iterator rather confusing.  Wjy not simply:
> >
> >               next = s.ulong[0];
> >               while (count >= bytes_long + mask) {
> >                       ...
> >                       count -= bytes_long;
> >               }
>
> My fist attack on long 'for' statements is just to move the
> initialisation to the previous line.
> Then make sure there is nothing in the comparison that needs
> to be calculated every iteration.
> I suspect you can subtract 'mask' from 'count'.
> Giving:
>                 count -= mask;
>                 next = s.ulong[0];
>                 for (;; count > bytes_long; count -= bytes_long) {
>

This way we'll lose the remainder, as count is used at the end to copy
the leftover.
Anyway, both bytes_long and mask are constant, I doubt they get summed
at every cycle.

> Next is to shorten the variable names!
>
>         David
>

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