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/* ----------------------------------------------------------------------
* Project: CMSIS DSP Library
* Title: arm_biquad_cascade_df1_init_q31.c
* Description: Q31 Biquad cascade DirectFormI(DF1) filter initialization function
*
* $Date: 18. March 2019
* $Revision: V1.6.0
*
* Target Processor: Cortex-M cores
* -------------------------------------------------------------------- */
/*
* Copyright (C) 2010-2019 ARM Limited or its affiliates. All rights reserved.
*
* SPDX-License-Identifier: Apache-2.0
*
* Licensed under the Apache License, Version 2.0 (the License); you may
* not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an AS IS BASIS, WITHOUT
* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#include "arm_math.h"
/**
@ingroup groupFilters
*/
/**
@addtogroup BiquadCascadeDF1
@{
*/
/**
@brief Initialization function for the Q31 Biquad cascade filter.
@param[in,out] S points to an instance of the Q31 Biquad cascade structure.
@param[in] numStages number of 2nd order stages in the filter.
@param[in] pCoeffs points to the filter coefficients.
@param[in] pState points to the state buffer.
@param[in] postShift Shift to be applied after the accumulator. Varies according to the coefficients format
@return none
@par Coefficient and State Ordering
The coefficients are stored in the array <code>pCoeffs</code> in the following order:
<pre>
{b10, b11, b12, a11, a12, b20, b21, b22, a21, a22, ...}
</pre>
@par
where <code>b1x</code> and <code>a1x</code> are the coefficients for the first stage,
<code>b2x</code> and <code>a2x</code> are the coefficients for the second stage,
and so on. The <code>pCoeffs</code> array contains a total of <code>5*numStages</code> values.
@par
The <code>pState</code> points to state variables array.
Each Biquad stage has 4 state variables <code>x[n-1], x[n-2], y[n-1],</code> and <code>y[n-2]</code>.
The state variables are arranged in the <code>pState</code> array as:
<pre>
{x[n-1], x[n-2], y[n-1], y[n-2]}
</pre>
The 4 state variables for stage 1 are first, then the 4 state variables for stage 2, and so on.
The state array has a total length of <code>4*numStages</code> values.
The state variables are updated after each block of data is processed; the coefficients are untouched.
*/
void arm_biquad_cascade_df1_init_q31(
arm_biquad_casd_df1_inst_q31 * S,
uint8_t numStages,
const q31_t * pCoeffs,
q31_t * pState,
int8_t postShift)
{
/* Assign filter stages */
S->numStages = numStages;
/* Assign postShift to be applied to the output */
S->postShift = postShift;
/* Assign coefficient pointer */
S->pCoeffs = pCoeffs;
/* Clear state buffer and size is always 4 * numStages */
memset(pState, 0, (4U * (uint32_t) numStages) * sizeof(q31_t));
/* Assign state pointer */
S->pState = pState;
}
/**
@} end of BiquadCascadeDF1 group
*/
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