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White.h

/*
  dsp/White.h

      Copyright 2004 Tim Goetze <tim@quitte.de>

      simple white noise generator, based on Jon Dattorro's 3/2002 JAES 
      paper. quite an elegant design; consumes next to no CPU     on a processor
      providing a decent binary shift operator. most of all, no random() calls.

*/
/*
      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_WHITE_H_
#define _DSP_WHITE_H_

namespace DSP {

/* after initializing, call either get() or get_31() to get a sample, don't
 * mix them. (get_31 output goes out of range if called after get()).
 */
class White
{
      public:
            uint32 b;

            White()
                  {
                        b = 0x1fff7777;
                  }

            void init (float f)
                  {
                        b = (uint32) (f * (float) 0x1fff7777);
                  }
            
            d_sample abs()
                  {
                        return fabs (get());
                  }

            /* 32-bit version */
            d_sample get()
                  {
#                       define BIT(y) ((b << (31 - y)) & 0x80000000)

                        b = ((BIT (28) ^ BIT (27) ^ BIT (1) ^ BIT (0))) | (b >> 1);
                        return (4.6566128730773926e-10 * (d_sample) b) - 1;

#                       undef BIT
                  }

            /* 31-bit version, at least 6 instructions less / sample. probably only
             * pays off on a processor not providing a decent binary shift. */
            d_sample get_31()
                  {
#                       define BIT(y) ((b << (30 - y)) & 0x40000000)

                        b = ((BIT (3) ^ BIT (0))) | (b >> 1);
                        return (9.3132257461547852e-10 * (d_sample) b) - 1;

#                       undef BIT
                  }
};

} /* namespace DSP */

#endif /* _DSP_WHITE_H_ */

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