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Date: Thu, 23 Apr 2009 16:57:23 -0700 From: Andrew Morton <akpm@...ux-foundation.org> To: David Daney <ddaney@...iumnetworks.com> Cc: rpjday@...shcourse.ca, linux-kernel@...r.kernel.org Subject: Re: [PATCH] Introduce a boolean "single_bit_set" function. On Thu, 23 Apr 2009 12:57:11 -0700 David Daney <ddaney@...iumnetworks.com> wrote: > > +static inline __attribute__((const)) > > +bool single_bit_set(unsigned long n) > > +{ > > + return (n != 0 && ((n & (n - 1)) == 0)); > > +} > > + > > + > > > It would be nice to be able to override this per architecture. > > For example a more efficient implementation on CPUs that have a > population count instruction (__builtin_popcountl()) might be: > > static inline __attribute__((const)) > bool singe_bit_set(unsigned long n) > { > return __builtin_popcountl(n) == 1; > } Already done, via hweight_long(). -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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