251 lines
9.1 KiB
C
251 lines
9.1 KiB
C
/* ----------------------------------------------------------------------
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* Project: CMSIS DSP Library
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* Title: arm_biquad_cascade_df1_fast_q15.c
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* Description: Fast processing function for the Q15 Biquad cascade filter
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*
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* $Date: 18. March 2019
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* $Revision: V1.6.0
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*
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* Target Processor: Cortex-M cores
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* -------------------------------------------------------------------- */
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/*
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* Copyright (C) 2010-2019 ARM Limited or its affiliates. All rights reserved.
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*
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* SPDX-License-Identifier: Apache-2.0
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*
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* Licensed under the Apache License, Version 2.0 (the License); you may
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* not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an AS IS BASIS, WITHOUT
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* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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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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@brief Processing function for the Q15 Biquad cascade filter (fast variant).
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@param[in] S points to an instance of the Q15 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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@par Scaling and Overflow Behavior
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This fast version uses a 32-bit accumulator with 2.30 format.
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The accumulator maintains full precision of the intermediate multiplication results but provides only a single guard bit.
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Thus, if the accumulator result overflows it wraps around and distorts the 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).
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The 2.30 accumulator is then shifted by <code>postShift</code> bits and the result truncated to 1.15 format by discarding the low 16 bits.
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@remark
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Refer to \ref arm_biquad_cascade_df1_q15() for a slower implementation of this function
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which uses 64-bit accumulation to avoid wrap around distortion. Both the slow and the fast versions use the same instance structure.
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Use the function \ref arm_biquad_cascade_df1_init_q15() to initialize the filter structure.
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*/
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void arm_biquad_cascade_df1_fast_q15(
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const arm_biquad_casd_df1_inst_q15 * S,
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const q15_t * pSrc,
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q15_t * pDst,
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uint32_t blockSize)
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{
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const q15_t *pIn = pSrc; /* Source pointer */
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q15_t *pOut = pDst; /* Destination pointer */
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q15_t *pState = S->pState; /* State pointer */
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const q15_t *pCoeffs = S->pCoeffs; /* Coefficient pointer */
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q31_t acc; /* Accumulator */
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q31_t in; /* Temporary variable to hold input value */
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q31_t out; /* Temporary variable to hold output value */
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q31_t b0; /* Temporary variable to hold bo value */
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q31_t b1, a1; /* Filter coefficients */
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q31_t state_in, state_out; /* Filter state variables */
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int32_t shift = (int32_t) (15 - S->postShift); /* Post shift */
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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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/* Read the b0 and 0 coefficients using SIMD */
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b0 = read_q15x2_ia ((q15_t **) &pCoeffs);
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/* Read the b1 and b2 coefficients using SIMD */
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b1 = read_q15x2_ia ((q15_t **) &pCoeffs);
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/* Read the a1 and a2 coefficients using SIMD */
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a1 = read_q15x2_ia ((q15_t **) &pCoeffs);
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/* Read the input state values from the state buffer: x[n-1], x[n-2] */
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state_in = read_q15x2_ia (&pState);
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/* Read the output state values from the state buffer: y[n-1], y[n-2] */
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state_out = read_q15x2_da (&pState);
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#if defined (ARM_MATH_LOOPUNROLL)
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/* Apply loop unrolling and compute 2 output values simultaneously. */
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/* Variable acc 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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* 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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/* Loop unrolling: Compute 2 outputs at a time */
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sample = blockSize >> 1U;
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while (sample > 0U)
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{
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/* Read the input */
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in = read_q15x2_ia ((q15_t **) &pIn);
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/* out = b0 * x[n] + 0 * 0 */
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out = __SMUAD(b0, in);
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/* acc = b1 * x[n-1] + acc += b2 * x[n-2] + out */
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acc = __SMLAD(b1, state_in, out);
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/* acc += a1 * y[n-1] + acc += a2 * y[n-2] */
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acc = __SMLAD(a1, state_out, acc);
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/* The result is converted from 3.29 to 1.31 and then saturation is applied */
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out = __SSAT((acc >> shift), 16);
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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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/* x[n-N], x[n-N-1] are packed together to make state_in of type q31 */
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/* y[n-N], y[n-N-1] are packed together to make state_out of type q31 */
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#ifndef ARM_MATH_BIG_ENDIAN
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state_in = __PKHBT(in, state_in, 16);
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state_out = __PKHBT(out, state_out, 16);
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#else
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state_in = __PKHBT(state_in >> 16, (in >> 16), 16);
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state_out = __PKHBT(state_out >> 16, (out), 16);
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#endif /* #ifndef ARM_MATH_BIG_ENDIAN */
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/* out = b0 * x[n] + 0 * 0 */
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out = __SMUADX(b0, in);
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/* acc0 = b1 * x[n-1] , acc0 += b2 * x[n-2] + out */
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acc = __SMLAD(b1, state_in, out);
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/* acc += a1 * y[n-1] + acc += a2 * y[n-2] */
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acc = __SMLAD(a1, state_out, acc);
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/* The result is converted from 3.29 to 1.31 and then saturation is applied */
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out = __SSAT((acc >> shift), 16);
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/* Store the output in the destination buffer. */
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#ifndef ARM_MATH_BIG_ENDIAN
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write_q15x2_ia (&pOut, __PKHBT(state_out, out, 16));
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#else
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write_q15x2_ia (&pOut, __PKHBT(out, state_out >> 16, 16));
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#endif /* #ifndef ARM_MATH_BIG_ENDIAN */
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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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/* x[n-N], x[n-N-1] are packed together to make state_in of type q31 */
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/* y[n-N], y[n-N-1] are packed together to make state_out of type q31 */
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#ifndef ARM_MATH_BIG_ENDIAN
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state_in = __PKHBT(in >> 16, state_in, 16);
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state_out = __PKHBT(out, state_out, 16);
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#else
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state_in = __PKHBT(state_in >> 16, in, 16);
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state_out = __PKHBT(state_out >> 16, out, 16);
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#endif /* #ifndef ARM_MATH_BIG_ENDIAN */
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/* Decrement loop counter */
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sample--;
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}
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/* Loop unrolling: Compute remaining outputs */
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sample = (blockSize & 0x1U);
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#else
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/* Initialize blkCnt with number of samples */
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sample = blockSize;
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#endif /* #if defined (ARM_MATH_LOOPUNROLL) */
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while (sample > 0U)
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{
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/* Read the input */
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in = *pIn++;
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/* out = b0 * x[n] + 0 * 0 */
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#ifndef ARM_MATH_BIG_ENDIAN
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out = __SMUAD(b0, in);
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#else
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out = __SMUADX(b0, in);
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#endif /* #ifndef ARM_MATH_BIG_ENDIAN */
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/* acc = b1 * x[n-1], acc += b2 * x[n-2] + out */
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acc = __SMLAD(b1, state_in, out);
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/* acc += a1 * y[n-1] + acc += a2 * y[n-2] */
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acc = __SMLAD(a1, state_out, acc);
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/* The result is converted from 3.29 to 1.31 and then saturation is applied */
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out = __SSAT((acc >> shift), 16);
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/* Store the output in the destination buffer. */
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*pOut++ = (q15_t) out;
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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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/* x[n-N], x[n-N-1] are packed together to make state_in of type q31 */
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/* y[n-N], y[n-N-1] are packed together to make state_out of type q31 */
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#ifndef ARM_MATH_BIG_ENDIAN
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state_in = __PKHBT(in, state_in, 16);
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state_out = __PKHBT(out, state_out, 16);
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#else
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state_in = __PKHBT(state_in >> 16, in, 16);
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state_out = __PKHBT(state_out >> 16, out, 16);
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#endif /* #ifndef ARM_MATH_BIG_ENDIAN */
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/* decrement 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 (numStages - 1) occur in-place in the output buffer */
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pIn = pDst;
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/* Reset the output pointer */
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pOut = pDst;
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/* Store the updated state variables back into the state array */
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write_q15x2_ia(&pState, state_in);
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write_q15x2_ia(&pState, state_out);
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/* Decrement loop counter */
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stage--;
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} while (stage > 0U);
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}
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/**
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@} end of BiquadCascadeDF1 group
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*/
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