ref: 3192dd937a71f737af84273806d91b306526cece
dir: /libfaad/dither.c/
/* This program is licensed under the GNU Library General Public License, version 2,
* a copy of which is included with this program (with filename LICENSE.LGPL).
*
* (c) 2002 John Edwards
* mostly lifted from work by Frank Klemm
* random functions for dithering.
*
* last modified: $Id: dither.c,v 1.1 2002/08/13 19:16:07 menno Exp $
*/
#include "dither.h"
static const unsigned char Parity [256] = { // parity
0,1,1,0,1,0,0,1,1,0,0,1,0,1,1,0,1,0,0,1,0,1,1,0,0,1,1,0,1,0,0,1,
1,0,0,1,0,1,1,0,0,1,1,0,1,0,0,1,0,1,1,0,1,0,0,1,1,0,0,1,0,1,1,0,
1,0,0,1,0,1,1,0,0,1,1,0,1,0,0,1,0,1,1,0,1,0,0,1,1,0,0,1,0,1,1,0,
0,1,1,0,1,0,0,1,1,0,0,1,0,1,1,0,1,0,0,1,0,1,1,0,0,1,1,0,1,0,0,1,
1,0,0,1,0,1,1,0,0,1,1,0,1,0,0,1,0,1,1,0,1,0,0,1,1,0,0,1,0,1,1,0,
0,1,1,0,1,0,0,1,1,0,0,1,0,1,1,0,1,0,0,1,0,1,1,0,0,1,1,0,1,0,0,1,
0,1,1,0,1,0,0,1,1,0,0,1,0,1,1,0,1,0,0,1,0,1,1,0,0,1,1,0,1,0,0,1,
1,0,0,1,0,1,1,0,0,1,1,0,1,0,0,1,0,1,1,0,1,0,0,1,1,0,0,1,0,1,1,0
};
static unsigned int __r1 = 1;
static unsigned int __r2 = 1;
/*
* This is a simple random number generator with good quality for audio purposes.
* It consists of two polycounters with opposite rotation direction and different
* periods. The periods are coprime, so the total period is the product of both.
*
* -------------------------------------------------------------------------------------------------
* +-> |31:30:29:28:27:26:25:24:23:22:21:20:19:18:17:16:15:14:13:12:11:10: 9: 8: 7: 6: 5: 4: 3: 2: 1: 0|
* | -------------------------------------------------------------------------------------------------
* | | | | | | |
* | +--+--+--+-XOR-+--------+
* | |
* +--------------------------------------------------------------------------------------+
*
* -------------------------------------------------------------------------------------------------
* |31:30:29:28:27:26:25:24:23:22:21:20:19:18:17:16:15:14:13:12:11:10: 9: 8: 7: 6: 5: 4: 3: 2: 1: 0| <-+
* ------------------------------------------------------------------------------------------------- |
* | | | | |
* +--+----XOR----+--+ |
* | |
* +----------------------------------------------------------------------------------------+
*
*
* The first has an period of 3*5*17*257*65537, the second of 7*47*73*178481,
* which gives a period of 18.410.713.077.675.721.215. The result is the
* XORed values of both generators.
*/
unsigned int
random_int ( void )
{
unsigned int t1, t2, t3, t4;
t3 = t1 = __r1; t4 = t2 = __r2; // Parity calculation is done via table lookup, this is also available
t1 &= 0xF5; t2 >>= 25; // on CPUs without parity, can be implemented in C and avoid unpredictable
t1 = Parity [t1]; t2 &= 0x63; // jumps and slow rotate through the carry flag operations.
t1 <<= 31; t2 = Parity [t2];
return (__r1 = (t3 >> 1) | t1 ) ^ (__r2 = (t4 + t4) | t2 );
}
double
Random_Equi ( double mult ) // gives a equal distributed random number
{ // between -2^31*mult and +2^31*mult
return mult * (int) random_int ();
}
double
Random_Triangular ( double mult ) // gives a triangular distributed random number
{ // between -2^32*mult and +2^32*mult
return mult * ( (double) (int) random_int () + (double) (int) random_int () );
}
double
Init_Dither(int bits)
{
static unsigned char default_dither [] = { 92, 92, 88, 84, 81, 78, 74, 67, 0, 0 };
int index;
index = bits - 11;
if (index < 0) index = 0;
if (index > 9) index = 9;
Dither.Add = 0.5 * ((1L << (32 - bits)) - 1);
Dither.Dither = (0.01*default_dither[index]) / (((__int64)1) << bits);
}