White.h

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/*
  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);
                        }
                
                sample_t abs()
                        {
                                return fabs (get());
                        }
 
                /* 32-bit version */
                sample_t get()
                        {
#                               define BIT(y) ((b << (31 - y)) & 0x80000000)
 
                                b = ((BIT (28) ^ BIT (27) ^ BIT (1) ^ BIT (0))) | (b >> 1);
                                return (4.6566128730773926e-10 * (sample_t) 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. */
                sample_t get_31()
                        {
#                               define BIT(y) ((b << (30 - y)) & 0x40000000)
 
                                b = ((BIT (3) ^ BIT (0))) | (b >> 1);
                                return (9.3132257461547852e-10 * (sample_t) b) - 1;
 
#                               undef BIT
                        }
};
 
} /* namespace DSP */
 
#endif /* _DSP_WHITE_H_ */