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Issue #35 - implemented missing Int32_to_Int24_Dither function #798

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Issue #35 - implemented missing Int32_to_Int24_Dither function #798

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b122784
Implemented function "Int32_To_Int24_Dither".
whyismynamerudy Mar 19, 2023
806d4b9
added review comment
whyismynamerudy Mar 20, 2023
f1733cc
amended Int32_To_Int24_Dither following feedback; first attempt at im…
whyismynamerudy May 11, 2023
dea6d98
removed dither scaling
whyismynamerudy May 11, 2023
8dc7928
removed PaUtil_Generate24BitTriangularDither; implemented Phil's feed…
whyismynamerudy May 13, 2023
76c10e3
removed unnecessary "unused parameter" from Int32_To_Int24_Dither; in…
whyismynamerudy May 13, 2023
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46 changes: 33 additions & 13 deletions src/common/pa_converters.c
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Original file line number Diff line number Diff line change
Expand Up @@ -935,13 +935,30 @@ static void Int32_To_Int24_Dither(
void *sourceBuffer, signed int sourceStride,
unsigned int count, struct PaUtilTriangularDitherGenerator *ditherGenerator )
{
(void) destinationBuffer; /* unused parameters */
(void) destinationStride; /* unused parameters */
(void) sourceBuffer; /* unused parameters */
(void) sourceStride; /* unused parameters */
(void) count; /* unused parameters */
(void) ditherGenerator; /* unused parameters */
/* IMPLEMENT ME */

PaInt32 *src = (PaInt32*)sourceBuffer;
unsigned char *dest = (unsigned char*)destinationBuffer;
PaInt32 *scaledDitherResult = (PaInt32*)destinationBuffer;
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@RossBencina RossBencina May 19, 2023

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The most obvious red flag here is that you're casting a non-aligned ptr to a 32-bit aligned pointer. But also, why is the scaled dither result being stored in the destination buffer? In any case there's no reason to be storing a temporary result in the destination buffer.

Suggested change
PaInt32 *scaledDitherResult = (PaInt32*)destinationBuffer;

PaInt32 dither;
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@RossBencina RossBencina May 19, 2023

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Suggested change
PaInt32 dither;


while ( count-- )
{
/* REVIEW */
dither = PaUtil_Generate16BitTriangularDither(ditherGenerator);
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@RossBencina RossBencina May 19, 2023

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Suggested change
dither = PaUtil_Generate16BitTriangularDither(ditherGenerator);
PaInt32 dither = PaUtil_Generate16BitTriangularDither(ditherGenerator);

*scaledDitherResult = (PaInt32) ((((*src) >> 1) + dither) >> 7);
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@RossBencina RossBencina May 19, 2023

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Suggested change
*scaledDitherResult = (PaInt32) ((((*src) >> 1) + dither) >> 7);
PaInt32 scaledDitherResult = (PaInt32) ((((*src) >> 1) + dither) >> 7);


#if defined(PA_LITTLE_ENDIAN)
dest[0] = (unsigned char)(*scaledDitherResult);
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@RossBencina RossBencina May 19, 2023

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remove the * now.

dest[1] = (unsigned char)(*scaledDitherResult >> 8);
dest[2] = (unsigned char)(*scaledDitherResult >> 16);
#elif defined(PA_BIG_ENDIAN)
dest[0] = (unsigned char)(*scaledDitherResult >> 16);
dest[1] = (unsigned char)(*scaledDitherResult >> 8);
dest[2] = (unsigned char)(*scaledDitherResult);
#endif
src += sourceStride;
dest += destinationStride * 3;
}
}

/* -------------------------------------------------------------------------- */
Expand Down Expand Up @@ -1055,16 +1072,19 @@ static void Int32_To_UInt8_Dither(
void *sourceBuffer, signed int sourceStride,
unsigned int count, struct PaUtilTriangularDitherGenerator *ditherGenerator )
{
/* PaInt32 *src = (PaInt32*)sourceBuffer;
unsigned char *dest = (unsigned char*)destinationBuffer; */
(void)ditherGenerator; /* unused parameter */
PaInt32 *src = (PaInt32*)sourceBuffer;
unsigned char *dest = (unsigned char*)destinationBuffer;
PaInt32 dither;

while( count-- )
{
/* IMPLEMENT ME */
/* REVIEW */
dither = PaUtil_Generate16BitTriangularDither( ditherGenerator );
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@RossBencina RossBencina May 19, 2023

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declare variable here as in previous function.

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@philburk philburk May 19, 2023

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dither could be declared here.


/* src += sourceStride;
dest += destinationStride; */
*dest = (unsigned char)((((*src) >> 1) + dither) >> 23);
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@philburk philburk May 19, 2023

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UInt8 audio is centered around 128 and ranges from 0 to 255.
So silence would be all 128s.

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@philburk philburk Jun 30, 2023

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To clarify, you need to add an offset to convert Int32 to Uint8 format.


src += sourceStride;
dest += destinationStride;
}
}

Expand Down