From owner-freebsd-hackers  Sat Aug 21 10:13:35 1999
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To: Nick Hibma <hibma@skylink.it>
Cc: FreeBSD Hackers mailing list <hackers@FreeBSD.ORG>
Subject: Re: from number to power of two 
In-reply-to: Your message of "Sat, 21 Aug 1999 12:54:32 +0200."
             <Pine.BSF.4.10.9908211250310.7595-100000@heidi.plazza.it> 
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Date: Sat, 21 Aug 1999 19:11:35 +0200
From: Johan Karlsson <k@numeri.campus.luth.se>
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At Sat, 21 Aug 1999 12:54:32 +0200, Nick Hibma wrote:
>
>Does anyone know an inexpensive algorithm (O(1)) to go from an number to
>the next (lower or higher) power of two.
>
>1			-> 1
>2,3			-> 2
>4,5,6,7			-> 4
>8,9,10,11,12,13,14,15	-> 8
>etc.
>
>So %1101 should become either %10000 or %1000.
>
>The only solution I have so far is a table. That is a possibility as the
>the highest number will be 32 I think.

This small prog works at least on x86

=====
#include <sys/types.h>
#include <machine/cpufunc.h>

int 
main(int argc, char **argv){
  int i, j, k;

  sscanf(argv[1], "%d", &i);

  j = 1<<(fls(i)-1);
  k = 1<<(fls(i-1));

  printf("%d %d %d\n", j, i, k);

  return 0;

} 
=====

/Johan K



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