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/*
* $Id: pa_dither.c,v 1.1.2.3 2002/06/16 13:11:02 rossbencina Exp $
* Portable Audio I/O Library triangular dither generator
*
* Based on the Open Source API proposed by Ross Bencina
* Copyright (c) 1999-2002 Phil Burk, Ross Bencina
*
* Permission is hereby granted, free of charge, to any person obtaining
* a copy of this software and associated documentation files
* (the "Software"), to deal in the Software without restriction,
* including without limitation the rights to use, copy, modify, merge,
* publish, distribute, sublicense, and/or sell copies of the Software,
* and to permit persons to whom the Software is furnished to do so,
* subject to the following conditions:
*
* The above copyright notice and this permission notice shall be
* included in all copies or substantial portions of the Software.
*
* Any person wishing to distribute modifications to the Software is
* requested to send the modifications to the original developer so that
* they can be incorporated into the canonical version.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR
* ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF
* CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
* WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*/
#include "pa_dither.h"
#define PA_DITHER_BITS_ (15)
void PaUtil_InitializeTriangularDitherState( PaUtilTriangularDitherGenerator *state )
{
state->previous = 0;
state->randSeed1 = 22222;
state->randSeed2 = 5555555;
}
signed long PaUtil_Generate16BitTriangularDither( PaUtilTriangularDitherGenerator *state )
{
signed long current, highPass;
/* Generate two random numbers. */
state->randSeed1 = (state->randSeed1 * 196314165) + 907633515;
state->randSeed2 = (state->randSeed2 * 196314165) + 907633515;
/* Generate triangular distribution about 0.
* Shift before adding to prevent overflow which would skew the distribution.
* Also shift an extra bit for the high pass filter.
*/
#define DITHER_SHIFT_ ((32 - PA_DITHER_BITS_) + 1)
current = (((signed long)state->randSeed1)>>DITHER_SHIFT_) +
(((signed long)state->randSeed2)>>DITHER_SHIFT_);
/* High pass filter to reduce audibility. */
highPass = current - state->previous;
state->previous = current;
return highPass;
}
/* Multiply by PA_FLOAT_DITHER_SCALE_ to get a float between -2.0 and +1.99999 */
#define PA_FLOAT_DITHER_SCALE_ (1.0f / ((1<<PA_DITHER_BITS_)-1))
static const float const_float_dither_scale_ = PA_FLOAT_DITHER_SCALE_;
float PaUtil_GenerateFloatTriangularDither( PaUtilTriangularDitherGenerator *state )
{
signed long current, highPass;
/* Generate two random numbers. */
state->randSeed1 = (state->randSeed1 * 196314165) + 907633515;
state->randSeed2 = (state->randSeed2 * 196314165) + 907633515;
/* Generate triangular distribution about 0.
* Shift before adding to prevent overflow which would skew the distribution.
* Also shift an extra bit for the high pass filter.
*/
#define DITHER_SHIFT_ ((32 - PA_DITHER_BITS_) + 1)
current = (((signed long)state->randSeed1)>>DITHER_SHIFT_) +
(((signed long)state->randSeed2)>>DITHER_SHIFT_);
/* High pass filter to reduce audibility. */
highPass = current - state->previous;
state->previous = current;
return ((float)highPass) * const_float_dither_scale_;
}
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