linux-kernel - Re: [RFC PATCH v2 10/15] cpu-model/s390: Add cpu class initialization routines

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Date:	Fri, 20 Feb 2015 10:11:55 -0800
From:	Richard Henderson <rth@...ddle.net>
To:	Michael Mueller <mimu@...ux.vnet.ibm.com>, qemu-devel@...gnu.org,
	kvm@...r.kernel.org, linux-s390@...r.kernel.org,
	linux-kernel@...r.kernel.org
CC:	Gleb Natapov <gleb@...nel.org>, Alexander Graf <agraf@...e.de>,
	Christian Borntraeger <borntraeger@...ibm.com>,
	"Jason J. Herne" <jjherne@...ux.vnet.ibm.com>,
	Cornelia Huck <cornelia.huck@...ibm.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Andreas Faerber <afaerber@...e.de>
Subject: Re: [RFC PATCH v2 10/15] cpu-model/s390: Add cpu class initialization
 routines

On 02/17/2015 06:24 AM, Michael Mueller wrote:
> +static inline uint64_t big_endian_bit(unsigned long nr)
> +{
> +    return 1ul << (BITS_PER_LONG - (nr % BITS_PER_LONG));
> +};

This is buggy.  NR=0 should map to 63, not 64.

> +    return !!(*ptr & big_endian_bit(nr));

Personally I dislike !! as an idiom.  Given that big_endian_bit isn't used
anywhere else, can we integrate it and change this to

static inline int test_facility(unsigned long nr, uint64_t *fac_list)
{
  unsigned long word = nr / BITS_PER_LONG;
  unsigned long be_bit = 63 - (nr % BITS_PER_LONG);
  return (fac_list[word] >> be_bit) & 1;
}


r~
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