/*-----------------------------------------------------------------------------
* Copyright (C) 2010-2014 ARM Limited. All rights reserved.
*
* $Date: 16/10/14 6:01p $Revision:  V.1.4.5
*
* Project:      CMSIS DSP Library
* Title:        arm_biquad_cascade_df1_init_q15.c
*
* Description:  Q15 Biquad cascade DirectFormI(DF1) filter initialization function.
*
* Target Processor: Cortex-M4/Cortex-M3/Cortex-M0
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*   - Redistributions of source code must retain the above copyright
*     notice, this list of conditions and the following disclaimer.
*   - Redistributions in binary form must reproduce the above copyright
*     notice, this list of conditions and the following disclaimer in
*     the documentation and/or other materials provided with the
*     distribution.
*   - Neither the name of ARM LIMITED nor the names of its contributors
*     may be used to endorse or promote products derived from this
*     software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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* ---------------------------------------------------------------------------*/

#include "arm_math.h"

/**
 * @ingroup groupFilters
 */

/**
 * @addtogroup BiquadCascadeDF1
 * @{
 */

/**
 * @details
 *
 * @param[in,out] *S           points to an instance of the Q15 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 to the accumulator result. Varies according to the coefficients format
 * @return        none
 *
 * <b>Coefficient and State Ordering:</b>
 *
 * \par
 * The coefficients are stored in the array <code>pCoeffs</code> in the following order:
 * <pre>
 *     {b10, 0, b11, b12, a11, a12, b20, 0, b21, b22, a21, a22, ...}
 * </pre>
 * 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>6*numStages</code> values.
 * The zero coefficient between <code>b1</code> and <code>b2</code> facilities  use of 16-bit SIMD instructions on the Cortex-M4.
 *
 * \par
 * The state variables are stored in the array <code>pState</code>.
 * 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_q15(
    arm_biquad_casd_df1_inst_q15 * S,
    uint8_t numStages,
    q15_t * pCoeffs,
    q15_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(q15_t));

    /* Assign state pointer */
    S->pState = pState;
}

/**
 * @} end of BiquadCascadeDF1 group
 */
