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#ifndef PA_DITHER_H
#define PA_DITHER_H
/*
* $Id$
* 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.
*
* 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.
*/
/*
* The text above constitutes the entire PortAudio license; however,
* the PortAudio community also makes the following non-binding requests:
*
* 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. It is also
* requested that these non-binding requests be included along with the
* license above.
*/
/** @file
@ingroup common_src
@brief Functions for generating dither noise
*/
#include "pa_types.h"
#ifdef __cplusplus
extern "C"
{
#endif /* __cplusplus */
/* Note that the linear congruential algorithm requires 32 bit integers
* because it uses arithmetic overflow. So use PaUint32 instead of
* unsigned long so it will work on 64 bit systems.
*/
/** @brief State needed to generate a dither signal */
typedef struct PaUtilTriangularDitherGenerator{
PaUint32 previous;
PaUint32 randSeed1;
PaUint32 randSeed2;
} PaUtilTriangularDitherGenerator;
/** @brief Initialize dither state */
void PaUtil_InitializeTriangularDitherState( PaUtilTriangularDitherGenerator *ditherState );
/**
@brief Calculate 2 LSB dither signal with a triangular distribution.
Ranged for adding to a 1 bit right-shifted 32 bit integer
prior to >>15. eg:
<pre>
signed long in = *
signed long dither = PaUtil_Generate16BitTriangularDither( ditherState );
signed short out = (signed short)(((in>>1) + dither) >> 15);
</pre>
@return
A signed 32-bit integer with a range of +32767 to -32768
*/
PaInt32 PaUtil_Generate16BitTriangularDither( PaUtilTriangularDitherGenerator *ditherState );
/**
@brief Calculate 2 LSB dither signal with a triangular distribution.
Ranged for adding to a pre-scaled float.
<pre>
float in = *
float dither = PaUtil_GenerateFloatTriangularDither( ditherState );
// use smaller scaler to prevent overflow when we add the dither
signed short out = (signed short)(in*(32766.0f) + dither );
</pre>
@return
A float with a range of -2.0 to +1.99999.
*/
float PaUtil_GenerateFloatTriangularDither( PaUtilTriangularDitherGenerator *ditherState );
#ifdef __cplusplus
}
#endif /* __cplusplus */
#endif /* PA_DITHER_H */
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