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/* Read yd (real), xd(imag) input */
U = pSrc[i3];
/* T = packed( (yb - yd), (xb - xd)) */
T = __QSUB16(T, U);
#ifndef ARM_MATH_BIG_ENDIAN
/* writing the butterfly processed i0 + fftLen/2 sample */
/* xb' = (xa-yb-xc+yd) */
/* yb' = (ya+xb-yc-xd) */
pSrc[i2] = __SHASX(S, T);
/* writing the butterfly processed i0 + 3fftLen/4 sample */
/* xd' = (xa+yb-xc-yd) */
/* yd' = (ya-xb-yc+xd) */
pSrc[i3] = __SHSAX(S, T);
#else
/* writing the butterfly processed i0 + fftLen/2 sample */
/* xb' = (xa-yb-xc+yd) */
/* yb' = (ya+xb-yc-xd) */
pSrc[i2] = __SHSAX(S, T);
/* writing the butterfly processed i0 + 3fftLen/4 sample */
/* xd' = (xa+yb-xc-yd) */
/* yd' = (ya-xb-yc+xd) */
pSrc[i3] = __SHASX(S, T);
#endif /* #ifndef ARM_MATH_BIG_ENDIAN */
}
/* end of last stage process */
/* output is in 11.5(q5) format for the 1024 point */
/* output is in 9.7(q7) format for the 256 point */
/* output is in 7.9(q9) format for the 64 point */
/* output is in 5.11(q11) format for the 16 point */
#else
/* Run the below code for Cortex-M0 */
q15_t R0, R1, S0, S1, T0, T1, U0, U1;
q15_t Co1, Si1, Co2, Si2, Co3, Si3, out1, out2;
uint32_t n1, n2, ic, i0, i1, i2, i3, j, k;
/* Total process is divided into three stages */
/* process first stage, middle stages, & last stage */
/* Initializations for the first stage */
n2 = fftLen;
n1 = n2;
/* n2 = fftLen/4 */
n2 >>= 2u;
/* Index for twiddle coefficient */
ic = 0u;
/* Index for input read and output write */
i0 = 0u;
j = n2;
/* Input is in 1.15(q15) format */
/* Start of first stage process */
do
{
/* Butterfly implementation */
/* index calculation for the input as, */
/* pSrc16[i0 + 0], pSrc16[i0 + fftLen/4], pSrc16[i0 + fftLen/2], pSrc16[i0 + 3fftLen/4] */
i1 = i0 + n2;
i2 = i1 + n2;
i3 = i2 + n2;
/* Reading i0, i0+fftLen/2 inputs */
/* input is down scale by 4 to avoid overflow */
/* Read ya (real), xa(imag) input */
T0 = pSrc16[i0 * 2u] >> 2u;
T1 = pSrc16[(i0 * 2u) + 1u] >> 2u;
/* input is down scale by 4 to avoid overflow */
/* Read yc (real), xc(imag) input */
S0 = pSrc16[i2 * 2u] >> 2u;
S1 = pSrc16[(i2 * 2u) + 1u] >> 2u;
/* R0 = (ya + yc), R1 = (xa + xc) */
R0 = __SSAT(T0 + S0, 16u);
R1 = __SSAT(T1 + S1, 16u);
/* S0 = (ya - yc), S1 = (xa - xc) */
S0 = __SSAT(T0 - S0, 16u);
S1 = __SSAT(T1 - S1, 16u);
/* Reading i0+fftLen/4 , i0+3fftLen/4 inputs */
/* input is down scale by 4 to avoid overflow */
/* Read yb (real), xb(imag) input */
T0 = pSrc16[i1 * 2u] >> 2u;
T1 = pSrc16[(i1 * 2u) + 1u] >> 2u;
/* Read yd (real), xd(imag) input */
/* input is down scale by 4 to avoid overflow */
U0 = pSrc16[i3 * 2u] >> 2u;
U1 = pSrc16[(i3 * 2u) + 1u] >> 2u;
/* T0 = (yb + yd), T1 = (xb + xd) */
T0 = __SSAT(T0 + U0, 16u);
T1 = __SSAT(T1 + U1, 16u);
/* writing the butterfly processed i0 sample */
/* xa' = xa + xb + xc + xd */
/* ya' = ya + yb + yc + yd */
pSrc16[i0 * 2u] = (R0 >> 1u) + (T0 >> 1u);
pSrc16[(i0 * 2u) + 1u] = (R1 >> 1u) + (T1 >> 1u);
/* R0 = (ya + yc) - (yb + yd), R1 = (xa + xc)- (xb + xd) */
R0 = __SSAT(R0 - T0, 16u);
R1 = __SSAT(R1 - T1, 16u);
/* co2 & si2 are read from Coefficient pointer */
Co2 = pCoef16[2u * ic * 2u];
Si2 = pCoef16[(2u * ic * 2u) + 1u];
/* xc' = (xa-xb+xc-xd)* co2 - (ya-yb+yc-yd)* (si2) */
out1 = (short) ((Co2 * R0 - Si2 * R1) >> 16u);
/* yc' = (ya-yb+yc-yd)* co2 + (xa-xb+xc-xd)* (si2) */
out2 = (short) ((Si2 * R0 + Co2 * R1) >> 16u);
/* Reading i0+fftLen/4 */
/* input is down scale by 4 to avoid overflow */
/* T0 = yb, T1 = xb */
T0 = pSrc16[i1 * 2u] >> 2u;
T1 = pSrc16[(i1 * 2u) + 1u] >> 2u;
/* writing the butterfly processed i0 + fftLen/4 sample */
/* writing output(xc', yc') in little endian format */
pSrc16[i1 * 2u] = out1;
pSrc16[(i1 * 2u) + 1u] = out2;
/* Butterfly calculations */
/* input is down scale by 4 to avoid overflow */
/* U0 = yd, U1 = xd) */
U0 = pSrc16[i3 * 2u] >> 2u;
U1 = pSrc16[(i3 * 2u) + 1u] >> 2u;
/* T0 = yb-yd, T1 = xb-xd) */
T0 = __SSAT(T0 - U0, 16u);
T1 = __SSAT(T1 - U1, 16u);
/* R0 = (ya-yc) - (xb- xd) , R1 = (xa-xc) + (yb-yd) */
R0 = (short) __SSAT((q31_t) (S0 + T1), 16);
R1 = (short) __SSAT((q31_t) (S1 - T0), 16);
/* S = (ya-yc) + (xb- xd), S1 = (xa-xc) - (yb-yd) */
S0 = (short) __SSAT((q31_t) (S0 - T1), 16);
S1 = (short) __SSAT((q31_t) (S1 + T0), 16);
/* co1 & si1 are read from Coefficient pointer */
Co1 = pCoef16[ic * 2u];
Si1 = pCoef16[(ic * 2u) + 1u];
/* Butterfly process for the i0+fftLen/2 sample */
/* xb' = (xa-yb-xc+yd)* co1 - (ya+xb-yc-xd)* (si1) */
out1 = (short) ((Co1 * S0 - Si1 * S1) >> 16u);
/* yb' = (ya+xb-yc-xd)* co1 + (xa-yb-xc+yd)* (si1) */
out2 = (short) ((Si1 * S0 + Co1 * S1) >> 16u);
/* writing output(xb', yb') in little endian format */
pSrc16[i2 * 2u] = out1;
pSrc16[(i2 * 2u) + 1u] = out2;
/* Co3 & si3 are read from Coefficient pointer */
Co3 = pCoef16[3u * ic * 2u];
Si3 = pCoef16[(3u * ic * 2u) + 1u];
/* Butterfly process for the i0+3fftLen/4 sample */
/* xd' = (xa+yb-xc-yd)* Co3 - (ya-xb-yc+xd)* (si3) */
out1 = (short) ((Co3 * R0 - Si3 * R1) >> 16u);
/* yd' = (ya-xb-yc+xd)* Co3 + (xa+yb-xc-yd)* (si3) */
out2 = (short) ((Si3 * R0 + Co3 * R1) >> 16u);
/* writing output(xd', yd') in little endian format */
pSrc16[i3 * 2u] = out1;
pSrc16[(i3 * 2u) + 1u] = out2;
/* Twiddle coefficients index modifier */
ic = ic + twidCoefModifier;
/* Updating input index */
i0 = i0 + 1u;
} while(--j);
/* End of first stage process */
/* data is in 4.11(q11) format */
/* Start of Middle stage process */
/* Twiddle coefficients index modifier */
twidCoefModifier <<= 2u;
/* Calculation of Middle stage */
for (k = fftLen / 4u; k > 4u; k >>= 2u)
{
/* Initializations for the middle stage */
n1 = n2;
n2 >>= 2u;
ic = 0u;
for (j = 0u; j <= (n2 - 1u); j++)
{
/* index calculation for the coefficients */
Co1 = pCoef16[ic * 2u];
Si1 = pCoef16[(ic * 2u) + 1u];
Co2 = pCoef16[2u * ic * 2u];
Si2 = pCoef16[2u * ic * 2u + 1u];
Co3 = pCoef16[3u * ic * 2u];
Si3 = pCoef16[(3u * ic * 2u) + 1u];
/* Twiddle coefficients index modifier */
ic = ic + twidCoefModifier;
/* Butterfly implementation */
for (i0 = j; i0 < fftLen; i0 += n1)
{
/* index calculation for the input as, */
/* pSrc16[i0 + 0], pSrc16[i0 + fftLen/4], pSrc16[i0 + fftLen/2], pSrc16[i0 + 3fftLen/4] */
i1 = i0 + n2;
i2 = i1 + n2;
i3 = i2 + n2;
/* Reading i0, i0+fftLen/2 inputs */
/* Read ya (real), xa(imag) input */
T0 = pSrc16[i0 * 2u];
T1 = pSrc16[(i0 * 2u) + 1u];
/* Read yc (real), xc(imag) input */
S0 = pSrc16[i2 * 2u];
S1 = pSrc16[(i2 * 2u) + 1u];
/* R0 = (ya + yc), R1 = (xa + xc) */
R0 = __SSAT(T0 + S0, 16u);
R1 = __SSAT(T1 + S1, 16u);
/* S0 = (ya - yc), S1 = (xa - xc) */
S0 = __SSAT(T0 - S0, 16u);
S1 = __SSAT(T1 - S1, 16u);
/* Reading i0+fftLen/4 , i0+3fftLen/4 inputs */
/* Read yb (real), xb(imag) input */
T0 = pSrc16[i1 * 2u];
T1 = pSrc16[(i1 * 2u) + 1u];
/* Read yd (real), xd(imag) input */
U0 = pSrc16[i3 * 2u];
U1 = pSrc16[(i3 * 2u) + 1u];
/* T0 = (yb + yd), T1 = (xb + xd) */
T0 = __SSAT(T0 + U0, 16u);
T1 = __SSAT(T1 + U1, 16u);
/* writing the butterfly processed i0 sample */
/* xa' = xa + xb + xc + xd */
/* ya' = ya + yb + yc + yd */
pSrc16[i0 * 2u] = ((R0 >> 1u) + (T0 >> 1u)) >> 1u;
pSrc16[(i0 * 2u) + 1u] = ((R1 >> 1u) + (T1 >> 1u)) >> 1u;
/* R0 = (ya + yc) - (yb + yd), R1 = (xa + xc) - (xb + xd) */
R0 = (R0 >> 1u) - (T0 >> 1u);
R1 = (R1 >> 1u) - (T1 >> 1u);
/* (ya-yb+yc-yd)* (si2) - (xa-xb+xc-xd)* co2 */
out1 = (short) ((Co2 * R0 - Si2 * R1) >> 16);
/* (ya-yb+yc-yd)* co2 + (xa-xb+xc-xd)* (si2) */
out2 = (short) ((Si2 * R0 + Co2 * R1) >> 16);
/* Reading i0+3fftLen/4 */
/* Read yb (real), xb(imag) input */
T0 = pSrc16[i1 * 2u];
T1 = pSrc16[(i1 * 2u) + 1u];
/* writing the butterfly processed i0 + fftLen/4 sample */
/* xc' = (xa-xb+xc-xd)* co2 - (ya-yb+yc-yd)* (si2) */
/* yc' = (ya-yb+yc-yd)* co2 + (xa-xb+xc-xd)* (si2) */
pSrc16[i1 * 2u] = out1;
pSrc16[(i1 * 2u) + 1u] = out2;
/* Butterfly calculations */
/* Read yd (real), xd(imag) input */
U0 = pSrc16[i3 * 2u];
U1 = pSrc16[(i3 * 2u) + 1u];
/* T0 = yb-yd, T1 = xb-xd) */
T0 = __SSAT(T0 - U0, 16u);
T1 = __SSAT(T1 - U1, 16u);
/* R0 = (ya-yc) - (xb- xd) , R1 = (xa-xc) + (yb-yd) */
R0 = (S0 >> 1u) + (T1 >> 1u);
R1 = (S1 >> 1u) - (T0 >> 1u);
/* S1 = (ya-yc) + (xb- xd), S1 = (xa-xc) - (yb-yd) */
S0 = (S0 >> 1u) - (T1 >> 1u);
S1 = (S1 >> 1u) + (T0 >> 1u);
/* Butterfly process for the i0+fftLen/2 sample */
out1 = (short) ((Co1 * S0 - Si1 * S1) >> 16u);
out2 = (short) ((Si1 * S0 + Co1 * S1) >> 16u);
/* xb' = (xa-yb-xc+yd)* co1 - (ya+xb-yc-xd)* (si1) */
/* yb' = (ya+xb-yc-xd)* co1 + (xa-yb-xc+yd)* (si1) */
pSrc16[i2 * 2u] = out1;
pSrc16[(i2 * 2u) + 1u] = out2;
/* Butterfly process for the i0+3fftLen/4 sample */
out1 = (short) ((Co3 * R0 - Si3 * R1) >> 16u);
out2 = (short) ((Si3 * R0 + Co3 * R1) >> 16u);
/* xd' = (xa+yb-xc-yd)* Co3 - (ya-xb-yc+xd)* (si3) */
/* yd' = (ya-xb-yc+xd)* Co3 + (xa+yb-xc-yd)* (si3) */
pSrc16[i3 * 2u] = out1;
pSrc16[(i3 * 2u) + 1u] = out2;
}
}
/* Twiddle coefficients index modifier */
twidCoefModifier <<= 2u;
}
/* End of Middle stages process */
/* data is in 10.6(q6) format for the 1024 point */
/* data is in 8.8(q8) format for the 256 point */
/* data is in 6.10(q10) format for the 64 point */
/* data is in 4.12(q12) format for the 16 point */
/* start of last stage process */
/* Initializations for the last stage */
n1 = n2;
n2 >>= 2u;
/* Butterfly implementation */
for (i0 = 0u; i0 <= (fftLen - n1); i0 += n1)
{
/* index calculation for the input as, */
/* pSrc16[i0 + 0], pSrc16[i0 + fftLen/4], pSrc16[i0 + fftLen/2], pSrc16[i0 + 3fftLen/4] */
i1 = i0 + n2;
i2 = i1 + n2;
i3 = i2 + n2;
/* Reading i0, i0+fftLen/2 inputs */
/* Read ya (real), xa(imag) input */
T0 = pSrc16[i0 * 2u];
T1 = pSrc16[(i0 * 2u) + 1u];
/* Read yc (real), xc(imag) input */
S0 = pSrc16[i2 * 2u];
S1 = pSrc16[(i2 * 2u) + 1u];
/* R0 = (ya + yc), R1 = (xa + xc) */
R0 = __SSAT(T0 + S0, 16u);
R1 = __SSAT(T1 + S1, 16u);
/* S0 = (ya - yc), S1 = (xa - xc) */
S0 = __SSAT(T0 - S0, 16u);
S1 = __SSAT(T1 - S1, 16u);
/* Reading i0+fftLen/4 , i0+3fftLen/4 inputs */
/* Read yb (real), xb(imag) input */
T0 = pSrc16[i1 * 2u];
T1 = pSrc16[(i1 * 2u) + 1u];
/* Read yd (real), xd(imag) input */
U0 = pSrc16[i3 * 2u];
U1 = pSrc16[(i3 * 2u) + 1u];
/* T0 = (yb + yd), T1 = (xb + xd) */
T0 = __SSAT(T0 + U0, 16u);
T1 = __SSAT(T1 + U1, 16u);
/* writing the butterfly processed i0 sample */
/* xa' = xa + xb + xc + xd */
/* ya' = ya + yb + yc + yd */
pSrc16[i0 * 2u] = (R0 >> 1u) + (T0 >> 1u);
pSrc16[(i0 * 2u) + 1u] = (R1 >> 1u) + (T1 >> 1u);
/* R0 = (ya + yc) - (yb + yd), R1 = (xa + xc) - (xb + xd) */
R0 = (R0 >> 1u) - (T0 >> 1u);
R1 = (R1 >> 1u) - (T1 >> 1u);
/* Read yb (real), xb(imag) input */
T0 = pSrc16[i1 * 2u];
T1 = pSrc16[(i1 * 2u) + 1u];
/* writing the butterfly processed i0 + fftLen/4 sample */
/* xc' = (xa-xb+xc-xd) */
/* yc' = (ya-yb+yc-yd) */
pSrc16[i1 * 2u] = R0;
pSrc16[(i1 * 2u) + 1u] = R1;
/* Read yd (real), xd(imag) input */
U0 = pSrc16[i3 * 2u];
U1 = pSrc16[(i3 * 2u) + 1u];
/* T0 = (yb - yd), T1 = (xb - xd) */
T0 = __SSAT(T0 - U0, 16u);
T1 = __SSAT(T1 - U1, 16u);
/* writing the butterfly processed i0 + fftLen/2 sample */
/* xb' = (xa-yb-xc+yd) */
/* yb' = (ya+xb-yc-xd) */
pSrc16[i2 * 2u] = (S0 >> 1u) - (T1 >> 1u);
pSrc16[(i2 * 2u) + 1u] = (S1 >> 1u) + (T0 >> 1u);
/* writing the butterfly processed i0 + 3fftLen/4 sample */
/* xd' = (xa+yb-xc-yd) */
/* yd' = (ya-xb-yc+xd) */
pSrc16[i3 * 2u] = (S0 >> 1u) + (T1 >> 1u);
pSrc16[(i3 * 2u) + 1u] = (S1 >> 1u) - (T0 >> 1u);
}
/* end of last stage process */
/* output is in 11.5(q5) format for the 1024 point */
/* output is in 9.7(q7) format for the 256 point */
/* output is in 7.9(q9) format for the 64 point */
/* output is in 5.11(q11) format for the 16 point */
#endif /* #ifndef ARM_MATH_CM0 */
}
/*
* @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.
*/
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;
}
}
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