RE: [linux-audio-dev] next power of two - Linux-audio-dev

17 Sep 2003

Very interesting,

"in the name of all DSP programmers" - thanksalot!

Do you have any estimation how many cycles this would spend on a pentium? I
would have make a wild guess of about 16-21 cycles + call overhead (if not
inlined)..

Hannes

P.S. Maybe you have similar code for the "bitreverse" operation.. ?  just
asking.. :)

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// Hannes Guddat
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...
  -----Original Message-----
 From: linux-audio-dev-admin(a)music.columbia.edu
 [mailto:linux-audio-dev-admin@music.columbia.edu]On Behalf Of
 Maarten de
 Boer
 Sent: Mittwoch, 17. September 2003 14:22
 To: linux-audio-dev(a)music.columbia.edu
 Subject: [linux-audio-dev] next power of two

 Hi,

 A colleague of mine found this very clever algoritm to calculate the
 next power of two for a given number. It comes from the
 Prophecy SDK for
 3d game development
 http://www.twilight3d.com/modules.php?op=modload&name=Download
 s&file=index

 Since this is a kind of thing often needed in audio
 processing, I wanted
 to share it with you. I certainly can not think of a faster (or more
 elegant) way of doing it.

 Maarten

          //////
          /// Returns the closest power-of-two number greater or equal
          /// to n for the given (unsigned) integer n.
          /// Will return 0 when n = 0 and 1 when n = 1.
          //////
          inline uint32_t nextPowerOfTwo(uint32_t n)
          {
                  --n;
                  n |= n >> 16;
                  n |= n >> 8;
                  n |= n >> 4;
                  n |= n >> 2;
                  n |= n >> 1;
                  ++n;
                  return n;
          }