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alvinlollo
2026-09-25 10:48:51 +10:00
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libraries/Adafruit_Zero_FFT_Library/fftutil.c
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/*
* fftutil.c
*
* Created on: Jan 5, 2018
* Author: deanm
*/
#include "Adafruit_ZeroFFT.h"
/*
* @brief In-place bit reversal function.
* @param[in, out] *pSrc points to the in-place buffer of Q15 data type.
* @param[in] fftLen length of the FFT.
* @param[in] bitRevFactor bit reversal modifier that supports different
* size FFTs with the same bit reversal table
* @param[in] *pBitRevTab points to bit reversal table.
* @return none.
*/
static q15_t ALIGN4 scratchData[ZERO_FFT_MAX];
void arm_bitreversal_q15(q15_t *pSrc16, uint32_t fftLen, uint16_t bitRevFactor,
uint16_t *pBitRevTab) {
q31_t *pSrc = (q31_t *)pSrc16;
q31_t in;
uint32_t fftLenBy2, fftLenBy2p1;
uint32_t i, j;
/* Initializations */
j = 0u;
fftLenBy2 = fftLen / 2u;
fftLenBy2p1 = (fftLen / 2u) + 1u;
/* Bit Reversal Implementation */
for (i = 0u; i <= (fftLenBy2 - 2u); i += 2u) {
if (i < j) {
/* pSrc[i] <-> pSrc[j]; */
/* pSrc[i+1u] <-> pSrc[j+1u] */
in = pSrc[i];
pSrc[i] = pSrc[j];
pSrc[j] = in;
/* pSrc[i + fftLenBy2p1] <-> pSrc[j + fftLenBy2p1]; */
/* pSrc[i + fftLenBy2p1+1u] <-> pSrc[j + fftLenBy2p1+1u] */
in = pSrc[i + fftLenBy2p1];
pSrc[i + fftLenBy2p1] = pSrc[j + fftLenBy2p1];
pSrc[j + fftLenBy2p1] = in;
}
/* pSrc[i+1u] <-> pSrc[j+fftLenBy2]; */
/* pSrc[i+2] <-> pSrc[j+fftLenBy2+1u] */
in = pSrc[i + 1u];
pSrc[i + 1u] = pSrc[j + fftLenBy2];
pSrc[j + fftLenBy2] = in;
/* Reading the index for the bit reversal */
j = *pBitRevTab;
/* Updating the bit reversal index depending on the fft length */
pBitRevTab += bitRevFactor;
}
}
void arm_radix2_butterfly_q15(q15_t *pSrc, uint32_t fftLen, q15_t *pCoef,
uint16_t twidCoefModifier) {
int i, j, k, l;
int n1, n2, ia;
q15_t xt, yt, cosVal, sinVal;
// N = fftLen;
n2 = fftLen;
n1 = n2;
n2 = n2 >> 1;
ia = 0;
// loop for groups
for (j = 0; j < n2; j++) {
cosVal = pCoef[ia * 2];
sinVal = pCoef[(ia * 2) + 1];
ia = ia + twidCoefModifier;
// loop for butterfly
for (i = j; i < fftLen; i += n1) {
l = i + n2;
xt = (pSrc[2 * i] >> 2u) - (pSrc[2 * l] >> 2u);
pSrc[2 * i] = ((pSrc[2 * i] >> 2u) + (pSrc[2 * l] >> 2u)) >> 1u;
yt = (pSrc[2 * i + 1] >> 2u) - (pSrc[2 * l + 1] >> 2u);
pSrc[2 * i + 1] =
((pSrc[2 * l + 1] >> 2u) + (pSrc[2 * i + 1] >> 2u)) >> 1u;
pSrc[2u * l] = (((int16_t)(((q31_t)xt * cosVal) >> 16)) +
((int16_t)(((q31_t)yt * sinVal) >> 16)));
pSrc[2u * l + 1u] = (((int16_t)(((q31_t)yt * cosVal) >> 16)) -
((int16_t)(((q31_t)xt * sinVal) >> 16)));
} // butterfly loop end
} // groups loop end
twidCoefModifier = twidCoefModifier << 1u;
// loop for stage
for (k = fftLen / 2; k > 2; k = k >> 1) {
n1 = n2;
n2 = n2 >> 1;
ia = 0;
// loop for groups
for (j = 0; j < n2; j++) {
cosVal = pCoef[ia * 2];
sinVal = pCoef[(ia * 2) + 1];
ia = ia + twidCoefModifier;
// loop for butterfly
for (i = j; i < fftLen; i += n1) {
l = i + n2;
xt = pSrc[2 * i] - pSrc[2 * l];
pSrc[2 * i] = (pSrc[2 * i] + pSrc[2 * l]) >> 1u;
yt = pSrc[2 * i + 1] - pSrc[2 * l + 1];
pSrc[2 * i + 1] = (pSrc[2 * l + 1] + pSrc[2 * i + 1]) >> 1u;
pSrc[2u * l] = (((int16_t)(((q31_t)xt * cosVal) >> 16)) +
((int16_t)(((q31_t)yt * sinVal) >> 16)));
pSrc[2u * l + 1u] = (((int16_t)(((q31_t)yt * cosVal) >> 16)) -
((int16_t)(((q31_t)xt * sinVal) >> 16)));
} // butterfly loop end
} // groups loop end
twidCoefModifier = twidCoefModifier << 1u;
} // stages loop end
n1 = n2;
n2 = n2 >> 1;
ia = 0;
// loop for groups
for (j = 0; j < n2; j++) {
cosVal = pCoef[ia * 2];
sinVal = pCoef[(ia * 2) + 1];
ia = ia + twidCoefModifier;
// loop for butterfly
for (i = j; i < fftLen; i += n1) {
l = i + n2;
xt = pSrc[2 * i] - pSrc[2 * l];
pSrc[2 * i] = (pSrc[2 * i] + pSrc[2 * l]);
yt = pSrc[2 * i + 1] - pSrc[2 * l + 1];
pSrc[2 * i + 1] = (pSrc[2 * l + 1] + pSrc[2 * i + 1]);
pSrc[2u * l] = xt;
pSrc[2u * l + 1u] = yt;
} // butterfly loop end
} // groups loop end
twidCoefModifier = twidCoefModifier << 1u;
}
static inline void applyWindow(q15_t *src, const q15_t *window, uint16_t len) {
while (len--) {
int32_t val = *src * *window++;
*src++ = val >> 15;
}
}
int ZeroFFT(q15_t *source, uint16_t length) {
uint16_t twidCoefModifier;
uint16_t bitRevFactor;
uint16_t *pBitRevTable;
q15_t *pSrc = source;
switch (length) {
#if ZERO_FFT_MAX == 8192
case 4096u:
/* Initializations of structure parameters for 4096 point FFT */
/* Initialise the twiddle coef modifier value */
twidCoefModifier = 1u;
/* Initialise the bit reversal table modifier */
bitRevFactor = 1u;
/* Initialise the bit reversal table pointer */
pBitRevTable = (uint16_t *)armBitRevTable;
applyWindow(source, window_hanning_4096, 4096);
break;
#endif
#if ZERO_FFT_MAX >= 4096
case 2048u:
/* Initializations of structure parameters for 2048 point FFT */
/* Initialise the twiddle coef modifier value */
twidCoefModifier = 2u;
/* Initialise the bit reversal table modifier */
bitRevFactor = 2u;
/* Initialise the bit reversal table pointer */
pBitRevTable = (uint16_t *)&armBitRevTable[1];
applyWindow(source, window_hanning_2048, 2048);
break;
#endif
#if ZERO_FFT_MAX >= 2048
case 1024u:
/* Initializations of structure parameters for 1024 point FFT */
twidCoefModifier = 4u;
bitRevFactor = 4u;
pBitRevTable = (uint16_t *)&armBitRevTable[3];
applyWindow(source, window_hanning_1024, 1024);
break;
#endif
#if ZERO_FFT_MAX >= 1024
case 512u:
/* Initializations of structure parameters for 512 point FFT */
twidCoefModifier = 8u;
bitRevFactor = 8u;
pBitRevTable = (uint16_t *)&armBitRevTable[7];
applyWindow(source, window_hanning_512, 512);
break;
#endif
#if ZERO_FFT_MAX >= 512
case 256u:
/* Initializations of structure parameters for 256 point FFT */
twidCoefModifier = 16u;
bitRevFactor = 16u;
pBitRevTable = (uint16_t *)&armBitRevTable[15];
applyWindow(source, window_hanning_256, 256);
break;
#endif
case 128u:
/* Initializations of structure parameters for 128 point FFT */
twidCoefModifier = 32u;
bitRevFactor = 32u;
pBitRevTable = (uint16_t *)&armBitRevTable[31];
applyWindow(source, window_hanning_128, 128);
break;
case 64u:
/* Initializations of structure parameters for 64 point FFT */
twidCoefModifier = 64u;
bitRevFactor = 64u;
pBitRevTable = (uint16_t *)&armBitRevTable[63];
applyWindow(source, window_hanning_64, 64);
break;
case 32u:
/* Initializations of structure parameters for 32 point FFT */
twidCoefModifier = 128u;
bitRevFactor = 128u;
pBitRevTable = (uint16_t *)&armBitRevTable[127];
applyWindow(source, window_hanning_32, 32);
break;
case 16u:
/* Initializations of structure parameters for 16 point FFT */
twidCoefModifier = 256u;
bitRevFactor = 256u;
pBitRevTable = (uint16_t *)&armBitRevTable[255];
applyWindow(source, window_hanning_16, 16);
break;
default:
/* Reporting argument error if fftSize is not valid value */
return -1;
break;
}
// split the data
q15_t *pOut = scratchData;
for (int i = 0; i < length; i++) {
*pOut++ = *pSrc++; // real
*pOut++ = 0; // imaginary
}
arm_radix2_butterfly_q15(scratchData, length, (q15_t *)twiddleCoefQ15,
twidCoefModifier);
arm_bitreversal_q15(scratchData, length, bitRevFactor, pBitRevTable);
pSrc = source;
pOut = scratchData;
for (int i = 0; i < length; i++) {
q15_t val = *pOut++;
uint32_t v = abs(val);
*pSrc++ = v;
pOut++; // discard imaginary phase val
}
return 0;
}