ref: 6b2df7a57294c528efc25765d7069407e9bdd4e8
dir: /src/pt2_downsample2x.c/
// for finding memory leaks in debug mode with Visual Studio
#if defined _DEBUG && defined _MSC_VER
#include <crtdbg.h>
#endif
/* High-quality /2 decimator from
** https://www.musicdsp.org/en/latest/Filters/231-hiqh-quality-2-decimators.html
*/
#include <stdint.h>
#include <stdbool.h>
#include <math.h> // round()
#include "pt2_helpers.h" // ABS()
// ----------------------------------------------------------
// reserved for main audio channel mixer, PAT2SMP and MOD2WAV
// ----------------------------------------------------------
static double R1_L, R2_L, R3_L, R4_L, R5_L, R6_L, R7_L, R8_L, R9_L;
static double R1_R, R2_R, R3_R, R4_R, R5_R, R6_R, R7_R, R8_R, R9_R;
void clearMixerDownsamplerStates(void)
{
R1_L = R2_L = R3_L = R4_L = R5_L = R6_L = R7_L = R8_L = R9_L = 0.0;
R1_R = R2_R = R3_R = R4_R = R5_R = R6_R = R7_R = R8_R = R9_R = 0.0;
}
double decimate2x_L(double x0, double x1)
{
const double h0 = 8192.0 / 16384.0;
const double h1 = 5042.0 / 16384.0;
const double h3 = -1277.0 / 16384.0;
const double h5 = 429.0 / 16384.0;
const double h7 = -116.0 / 16384.0;
const double h9 = 18.0 / 16384.0;
double h9x0 = h9*x0;
double h7x0 = h7*x0;
double h5x0 = h5*x0;
double h3x0 = h3*x0;
double h1x0 = h1*x0;
double R10 = R9_L+h9x0;
R9_L = R8_L+h7x0;
R8_L = R7_L+h5x0;
R7_L = R6_L+h3x0;
R6_L = R5_L+h1x0;
R5_L = R4_L+h1x0+h0*x1;
R4_L = R3_L+h3x0;
R3_L = R2_L+h5x0;
R2_L = R1_L+h7x0;
R1_L = h9x0;
return R10;
}
double decimate2x_R(double x0, double x1)
{
const double h0 = 8192.0 / 16384.0;
const double h1 = 5042.0 / 16384.0;
const double h3 = -1277.0 / 16384.0;
const double h5 = 429.0 / 16384.0;
const double h7 = -116.0 / 16384.0;
const double h9 = 18.0 / 16384.0;
double h9x0 = h9*x0;
double h7x0 = h7*x0;
double h5x0 = h5*x0;
double h3x0 = h3*x0;
double h1x0 = h1*x0;
double R10 = R9_R+h9x0;
R9_R = R8_R+h7x0;
R8_R = R7_R+h5x0;
R7_R = R6_R+h3x0;
R6_R = R5_R+h1x0;
R5_R = R4_R+h1x0+h0*x1;
R4_R = R3_R+h3x0;
R3_R = R2_R+h5x0;
R2_R = R1_R+h7x0;
R1_R = h9x0;
return R10;
}
// ----------------------------------------------------------
// ----------------------------------------------------------
// ----------------------------------------------------------
static double R1, R2, R3, R4, R5, R6, R7, R8, R9;
static void clearDownsamplerState(void)
{
R1 = R2 = R3 = R4 = R5 = R6 = R7 = R8 = R9 = 0.0;
}
static double decimate2x(double x0, double x1)
{
const double h0 = 8192.0 / 16384.0;
const double h1 = 5042.0 / 16384.0;
const double h3 = -1277.0 / 16384.0;
const double h5 = 429.0 / 16384.0;
const double h7 = -116.0 / 16384.0;
const double h9 = 18.0 / 16384.0;
double h9x0 = h9*x0;
double h7x0 = h7*x0;
double h5x0 = h5*x0;
double h3x0 = h3*x0;
double h1x0 = h1*x0;
double R10 = R9+h9x0;
R9 = R8+h7x0;
R8 = R7+h5x0;
R7 = R6+h3x0;
R6 = R5+h1x0;
R5 = R4+h1x0+h0*x1;
R4 = R3+h3x0;
R3 = R2+h5x0;
R2 = R1+h7x0;
R1 = h9x0;
return R10;
}
// Warning: These can exceed original range because of undershoot/overshoot!
void downsample2xDouble(double *buffer, uint32_t originalLength)
{
clearDownsamplerState();
const double *input = buffer;
const uint32_t length = originalLength / 2;
for (uint32_t i = 0; i < length; i++, input += 2)
buffer[i] = decimate2x(input[0], input[1]);
}
void downsample2xFloat(float *buffer, uint32_t originalLength)
{
clearDownsamplerState();
const float *input = buffer;
const uint32_t length = originalLength / 2;
for (uint32_t i = 0; i < length; i++, input += 2)
buffer[i] = (float)decimate2x(input[0], input[1]);
}
// Warning: These are slow and use normalization to prevent clipping from undershoot/overshoot!
bool downsample2x8BitU(uint8_t *buffer, uint32_t originalLength)
{
double *dBuffer = (double *)malloc(originalLength * sizeof (double));
if (dBuffer == NULL)
return false;
for (uint32_t i = 0; i < originalLength; i++)
dBuffer[i] = (buffer[i] - 128) * (1.0 / (INT8_MAX+1.0));
const double *input = dBuffer;
double dPeak = 0.0;
clearDownsamplerState();
const uint32_t length = originalLength / 2;
for (uint32_t i = 0; i < length; i++, input += 2)
{
double dOut = decimate2x(input[0], input[1]);
dBuffer[i] = dOut;
dOut = ABS(dOut);
if (dOut > dPeak)
dPeak = dOut;
}
// normalize
double dAmp = 1.0;
if (dPeak > 0.0)
dAmp = INT8_MAX / dPeak;
for (uint32_t i = 0; i < length; i++)
{
double dSmp = dBuffer[i] * dAmp;
// faster than calling round()
if (dSmp < 0.0) dSmp -= 0.5;
else if (dSmp > 0.0) dSmp += 0.5;
buffer[i] = (uint8_t)dSmp + 128;
}
free(dBuffer);
return true;
}
bool downsample2x8Bit(int8_t *buffer, uint32_t originalLength)
{
double *dBuffer = (double *)malloc(originalLength * sizeof (double));
if (dBuffer == NULL)
return false;
for (uint32_t i = 0; i < originalLength; i++)
dBuffer[i] = buffer[i] * (1.0 / (INT8_MAX+1.0));
const double *input = dBuffer;
double dPeak = 0.0;
clearDownsamplerState();
const uint32_t length = originalLength / 2;
for (uint32_t i = 0; i < length; i++, input += 2)
{
double dOut = decimate2x(input[0], input[1]);
dBuffer[i] = dOut;
dOut = ABS(dOut);
if (dOut > dPeak)
dPeak = dOut;
}
// normalize
double dAmp = 1.0;
if (dPeak > 0.0)
dAmp = INT8_MAX / dPeak;
for (uint32_t i = 0; i < length; i++)
{
double dSmp = dBuffer[i] * dAmp;
// faster than calling round()
if (dSmp < 0.0) dSmp -= 0.5;
else if (dSmp > 0.0) dSmp += 0.5;
buffer[i] = (int8_t)dSmp;
}
free(dBuffer);
return true;
}
bool downsample2x16Bit(int16_t *buffer, uint32_t originalLength)
{
double *dBuffer = (double *)malloc(originalLength * sizeof (double));
if (dBuffer == NULL)
return false;
for (uint32_t i = 0; i < originalLength; i++)
dBuffer[i] = buffer[i] * (1.0 / (INT16_MAX+1.0));
const double *input = dBuffer;
double dPeak = 0.0;
clearDownsamplerState();
const uint32_t length = originalLength / 2;
for (uint32_t i = 0; i < length; i++, input += 2)
{
double dOut = decimate2x(input[0], input[1]);
dBuffer[i] = dOut;
dOut = ABS(dOut);
if (dOut > dPeak)
dPeak = dOut;
}
// normalize
double dAmp = 1.0;
if (dPeak > 0.0)
dAmp = INT16_MAX / dPeak;
for (uint32_t i = 0; i < length; i++)
{
double dSmp = dBuffer[i] * dAmp;
// faster than calling round()
if (dSmp < 0.0) dSmp -= 0.5;
else if (dSmp > 0.0) dSmp += 0.5;
buffer[i] = (int16_t)dSmp;
}
free(dBuffer);
return true;
}
bool downsample2x32Bit(int32_t *buffer, uint32_t originalLength)
{
double *dBuffer = (double *)malloc(originalLength * sizeof (double));
if (dBuffer == NULL)
return false;
for (uint32_t i = 0; i < originalLength; i++)
dBuffer[i] = buffer[i] * (1.0 / (INT32_MAX+1.0));
const double *input = dBuffer;
double dPeak = 0.0;
clearDownsamplerState();
const uint32_t length = originalLength / 2;
for (uint32_t i = 0; i < length; i++, input += 2)
{
double dOut = decimate2x(input[0], input[1]);
dBuffer[i] = dOut;
dOut = ABS(dOut);
if (dOut > dPeak)
dPeak = dOut;
}
// normalize
double dAmp = 1.0;
if (dPeak > 0.0)
dAmp = INT32_MAX / dPeak;
for (uint32_t i = 0; i < length; i++)
{
double dSmp = dBuffer[i] * dAmp;
// faster than calling round()
if (dSmp < 0.0) dSmp -= 0.5;
else if (dSmp > 0.0) dSmp += 0.5;
buffer[i] = (int32_t)dSmp;
}
free(dBuffer);
return true;
}