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From: Christoph Egger <Christoph.Egger@amd.com>
Subject: Re: [Qemu-devel] Re: [PATCH] Use ffs in favor of ffsll
Date: Thu, 2 Jul 2009 10:39:08 +0200
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To: qemu-devel@nongnu.org
Cc: Blue Swirl <blauwirbel@gmail.com>, Anthony Liguori <aliguori@us.ibm.com>, Jan Kiszka <jan.kiszka@web.de>

On Wednesday 01 July 2009 22:27:51 Blue Swirl wrote:
> On 7/1/09, Jan Kiszka <jan.kiszka@web.de> wrote:
> > Not all host platforms support the ll variant. This is not a critical
> >  path, so go the easy way.
> >
> >  -    for (i = 0; i < ARRAY_SIZE(env->interrupt_bitmap); i++) {
> >  -        bit = ffsll(env->interrupt_bitmap[i]);
> >  +    for (i = 0; i < sizeof(env->interrupt_bitmap) / sizeof(int); i++) {
> >  +        bit = ffs(((int *)env->interrupt_bitmap)[i]);
> >          if (bit) {
> >  -            pending_irq = i * 64 + bit - 1;
> >  +            pending_irq = i * 8 * sizeof(int) + bit - 1;
>
> I think this will not work on a big endian host.

A qemu_ffsll() implementation can be something like this:

int qemu_ffsll(long long mask)
{
      int bit;

      bit = ffs((int)mask);
      if (bit == 0) {
           mask >>= 32;
           bit = ffs((int)mask);
           if (bit) bit += 32;
      }
       return bit;
}

Christoph



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