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/* ----------------------------------------------------------------------
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* Copyright (C) 2010 ARM Limited. All rights reserved.
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*
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* $Date: 15. July 2011
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* $Revision: V1.0.10
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*
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* Project: CMSIS DSP Library
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* Title: arm_biquad_cascade_df1_fast_q31.c
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*
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* Description: Processing function for the
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* Q31 Fast Biquad cascade DirectFormI(DF1) filter.
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*
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* Target Processor: Cortex-M4/Cortex-M3
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*
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* Version 1.0.10 2011/7/15
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* Big Endian support added and Merged M0 and M3/M4 Source code.
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*
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* Version 1.0.3 2010/11/29
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* Re-organized the CMSIS folders and updated documentation.
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*
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* Version 1.0.2 2010/11/11
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* Documentation updated.
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*
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* Version 1.0.1 2010/10/05
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* Production release and review comments incorporated.
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*
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* Version 1.0.0 2010/09/20
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* Production release and review comments incorporated.
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*
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* Version 0.0.9 2010/08/27
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* Initial version
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*
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* -------------------------------------------------------------------- */
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#include "arm_math.h"
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/**
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* @ingroup groupFilters
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*/
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/**
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* @addtogroup BiquadCascadeDF1
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* @{
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*/
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/**
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* @details
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*
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* @param[in] *S points to an instance of the Q31 Biquad cascade structure.
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* @param[in] *pSrc points to the block of input data.
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* @param[out] *pDst points to the block of output data.
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* @param[in] blockSize number of samples to process per call.
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* @return none.
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*
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* <b>Scaling and Overflow Behavior:</b>
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* \par
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* This function is optimized for speed at the expense of fixed-point precision and overflow protection.
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* The result of each 1.31 x 1.31 multiplication is truncated to 2.30 format.
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* These intermediate results are added to a 2.30 accumulator.
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* Finally, the accumulator is saturated and converted to a 1.31 result.
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* The fast version has the same overflow behavior as the standard version and provides less precision since it discards the low 32 bits of each multiplication result.
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* In order to avoid overflows completely the input signal must be scaled down by two bits and lie in the range [-0.25 +0.25). Use the intialization function
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* arm_biquad_cascade_df1_init_q31() to initialize filter structure.
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*
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* \par
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* Refer to the function <code>arm_biquad_cascade_df1_q31()</code> for a slower implementation of this function which uses 64-bit accumulation to provide higher precision. Both the slow and the fast versions use the same instance structure.
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* Use the function <code>arm_biquad_cascade_df1_init_q31()</code> to initialize the filter structure.
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*/
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void arm_biquad_cascade_df1_fast_q31(
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const arm_biquad_casd_df1_inst_q31 * S,
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q31_t * pSrc,
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q31_t * pDst,
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uint32_t blockSize)
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{
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q31_t *pIn = pSrc; /* input pointer initialization */
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q31_t *pOut = pDst; /* output pointer initialization */
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q31_t *pState = S->pState; /* pState pointer initialization */
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q31_t *pCoeffs = S->pCoeffs; /* coeff pointer initialization */
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q31_t acc; /* accumulator */
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q31_t Xn1, Xn2, Yn1, Yn2; /* Filter state variables */
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q31_t b0, b1, b2, a1, a2; /* Filter coefficients */
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q31_t Xn; /* temporary input */
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int32_t shift = (int32_t) S->postShift + 1; /* Shift to be applied to the output */
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uint32_t sample, stage = S->numStages; /* loop counters */
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do
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{
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/* Reading the coefficients */
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b0 = *pCoeffs++;
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b1 = *pCoeffs++;
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b2 = *pCoeffs++;
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a1 = *pCoeffs++;
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a2 = *pCoeffs++;
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/* Reading the state values */
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Xn1 = pState[0];
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Xn2 = pState[1];
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Yn1 = pState[2];
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Yn2 = pState[3];
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/* Apply loop unrolling and compute 4 output values simultaneously. */
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/* The variables acc ... acc3 hold output values that are being computed:
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*
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* acc = b0 * x[n] + b1 * x[n-1] + b2 * x[n-2] + a1 * y[n-1] + a2 * y[n-2]
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*/
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sample = blockSize >> 2u;
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/* First part of the processing with loop unrolling. Compute 4 outputs at a time.
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** a second loop below computes the remaining 1 to 3 samples. */
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while(sample > 0u)
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{
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/* Read the input */
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Xn = *pIn++;
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/* acc = b0 * x[n] + b1 * x[n-1] + b2 * x[n-2] + a1 * y[n-1] + a2 * y[n-2] */
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/* acc = b0 * x[n] */
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acc = (q31_t) (((q63_t) b0 * Xn) >> 32);
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/* acc += b1 * x[n-1] */
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acc = (q31_t) ((((q63_t) acc << 32) + ((q63_t) b1 * (Xn1))) >> 32);
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/* acc += b[2] * x[n-2] */
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acc = (q31_t) ((((q63_t) acc << 32) + ((q63_t) b2 * (Xn2))) >> 32);
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/* acc += a1 * y[n-1] */
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acc = (q31_t) ((((q63_t) acc << 32) + ((q63_t) a1 * (Yn1))) >> 32);
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/* acc += a2 * y[n-2] */
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acc = (q31_t) ((((q63_t) acc << 32) + ((q63_t) a2 * (Yn2))) >> 32);
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/* The result is converted to 1.31 , Yn2 variable is reused */
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Yn2 = acc << shift;
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/* Store the output in the destination buffer. */
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*pOut++ = Yn2;
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/* Read the second input */
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Xn2 = *pIn++;
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/* acc = b0 * x[n] + b1 * x[n-1] + b2 * x[n-2] + a1 * y[n-1] + a2 * y[n-2] */
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/* acc = b0 * x[n] */
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acc = (q31_t) (((q63_t) b0 * (Xn2)) >> 32);
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/* acc += b1 * x[n-1] */
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acc = (q31_t) ((((q63_t) acc << 32) + ((q63_t) b1 * (Xn))) >> 32);
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/* acc += b[2] * x[n-2] */
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acc = (q31_t) ((((q63_t) acc << 32) + ((q63_t) b2 * (Xn1))) >> 32);
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/* acc += a1 * y[n-1] */
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acc = (q31_t) ((((q63_t) acc << 32) + ((q63_t) a1 * (Yn2))) >> 32);
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/* acc += a2 * y[n-2] */
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acc = (q31_t) ((((q63_t) acc << 32) + ((q63_t) a2 * (Yn1))) >> 32);
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/* The result is converted to 1.31, Yn1 variable is reused */
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Yn1 = acc << shift;
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/* Store the output in the destination buffer. */
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*pOut++ = Yn1;
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/* Read the third input */
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Xn1 = *pIn++;
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/* acc = b0 * x[n] + b1 * x[n-1] + b2 * x[n-2] + a1 * y[n-1] + a2 * y[n-2] */
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/* acc = b0 * x[n] */
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acc = (q31_t) (((q63_t) b0 * (Xn1)) >> 32);
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/* acc += b1 * x[n-1] */
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acc = (q31_t) ((((q63_t) acc << 32) + ((q63_t) b1 * (Xn2))) >> 32);
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/* acc += b[2] * x[n-2] */
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acc = (q31_t) ((((q63_t) acc << 32) + ((q63_t) b2 * (Xn))) >> 32);
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/* acc += a1 * y[n-1] */
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acc = (q31_t) ((((q63_t) acc << 32) + ((q63_t) a1 * (Yn1))) >> 32);
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/* acc += a2 * y[n-2] */
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acc = (q31_t) ((((q63_t) acc << 32) + ((q63_t) a2 * (Yn2))) >> 32);
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/* The result is converted to 1.31, Yn2 variable is reused */
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Yn2 = acc << shift;
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/* Store the output in the destination buffer. */
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*pOut++ = Yn2;
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/* Read the forth input */
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Xn = *pIn++;
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/* acc = b0 * x[n] + b1 * x[n-1] + b2 * x[n-2] + a1 * y[n-1] + a2 * y[n-2] */
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/* acc = b0 * x[n] */
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acc = (q31_t) (((q63_t) b0 * (Xn)) >> 32);
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/* acc += b1 * x[n-1] */
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acc = (q31_t) ((((q63_t) acc << 32) + ((q63_t) b1 * (Xn1))) >> 32);
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/* acc += b[2] * x[n-2] */
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acc = (q31_t) ((((q63_t) acc << 32) + ((q63_t) b2 * (Xn2))) >> 32);
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/* acc += a1 * y[n-1] */
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acc = (q31_t) ((((q63_t) acc << 32) + ((q63_t) a1 * (Yn2))) >> 32);
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/* acc += a2 * y[n-2] */
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acc = (q31_t) ((((q63_t) acc << 32) + ((q63_t) a2 * (Yn1))) >> 32);
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/* The result is converted to 1.31, Yn1 variable is reused */
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Yn1 = acc << shift;
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/* Every time after the output is computed state should be updated. */
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/* The states should be updated as: */
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/* Xn2 = Xn1 */
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/* Xn1 = Xn */
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/* Yn2 = Yn1 */
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/* Yn1 = acc */
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Xn2 = Xn1;
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Xn1 = Xn;
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/* Store the output in the destination buffer. */
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*pOut++ = Yn1;
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/* decrement the loop counter */
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sample--;
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}
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/* If the blockSize is not a multiple of 4, compute any remaining output samples here.
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** No loop unrolling is used. */
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sample = (blockSize & 0x3u);
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while(sample > 0u)
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{
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/* Read the input */
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Xn = *pIn++;
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/* acc = b0 * x[n] + b1 * x[n-1] + b2 * x[n-2] + a1 * y[n-1] + a2 * y[n-2] */
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/* acc = b0 * x[n] */
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acc = (q31_t) (((q63_t) b0 * (Xn)) >> 32);
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/* acc += b1 * x[n-1] */
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acc = (q31_t) ((((q63_t) acc << 32) + ((q63_t) b1 * (Xn1))) >> 32);
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/* acc += b[2] * x[n-2] */
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acc = (q31_t) ((((q63_t) acc << 32) + ((q63_t) b2 * (Xn2))) >> 32);
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/* acc += a1 * y[n-1] */
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acc = (q31_t) ((((q63_t) acc << 32) + ((q63_t) a1 * (Yn1))) >> 32);
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/* acc += a2 * y[n-2] */
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acc = (q31_t) ((((q63_t) acc << 32) + ((q63_t) a2 * (Yn2))) >> 32);
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/* The result is converted to 1.31 */
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acc = acc << shift;
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/* Every time after the output is computed state should be updated. */
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/* The states should be updated as: */
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/* Xn2 = Xn1 */
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/* Xn1 = Xn */
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/* Yn2 = Yn1 */
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/* Yn1 = acc */
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Xn2 = Xn1;
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Xn1 = Xn;
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Yn2 = Yn1;
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Yn1 = acc;
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/* Store the output in the destination buffer. */
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*pOut++ = acc;
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/* decrement the loop counter */
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sample--;
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}
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/* The first stage goes from the input buffer to the output buffer. */
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/* Subsequent stages occur in-place in the output buffer */
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pIn = pDst;
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/* Reset to destination pointer */
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pOut = pDst;
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/* Store the updated state variables back into the pState array */
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*pState++ = Xn1;
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*pState++ = Xn2;
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*pState++ = Yn1;
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*pState++ = Yn2;
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} while(--stage);
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}
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/**
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* @} end of BiquadCascadeDF1 group
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*/
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