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util.h

/*
      dsp/util.h
      
      Copyright 2002-4 Tim Goetze <tim@quitte.de>
      
      http://quitte.de/dsp/

      common math utility functions.

*/
/*
      This program is free software; you can redistribute it and/or
      modify it under the terms of the GNU General Public License
      as published by the Free Software Foundation; either version 2
      of the License, or (at your option) any later version.

      This program is distributed in the hope that it will be useful,
      but WITHOUT ANY WARRANTY; without even the implied warranty of
      MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
      GNU General Public License for more details.

      You should have received a copy of the GNU General Public License
      along with this program; if not, write to the Free Software
      Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
      02111-1307, USA or point your web browser to http://www.gnu.org.
*/

#ifndef _DSP_UTIL_H_
#define _DSP_UTIL_H_

namespace DSP {

inline int next_power_of_2 (int n)
{
      assert (n <= 0x40000000);

      int m = 1;
      
      while (m < n)
            m <<= 1;

      return m;
}

/* courtesy of Andrew Simper (vellocet.com) */
inline float
exp2_approx (float x)
{
      long * px = (long *) (&x); // store address of float as long pointer
      const float tx = (x - .5f) + (3 << 22); // temporary value for truncation
      const long  lx = *((long *) &tx) - 0x4b400000; // integer power of 2
      const float dx = x - (float) (lx); // float remainder of power of 2
      x = 1.f + dx * (0.6960656421638072f + // cubic apporoximation of 2^x
                                    dx * (0.224494337302845f +  // for x in the range [0, 1]
                                    dx * (0.07944023841053369f)));
      *px += (lx << 23); // add integer power of 2 to exponent

      return x;
}

inline bool
isprime (int v)
{
      if (v <= 3)
            return true;
      
      if (!(v & 1))
            return false;

      for (int i = 3; i < (int) sqrt (v) + 1; i += 2)
            if ((v % i) == 0)
                  return false;

      return true;
}

inline double 
db2lin (double db)
{
      return pow (10., db * .05);
}

inline double
lin2db (double lin)
{
      return 20. * log10 (lin);
}

} /* namespace DSP */

#endif /* _DSP_UTIL_H_ */

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