

#include "arm_math.h"

/**    
 * @ingroup groupFilters    
 */

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

/**    
 * @details    
 *    
 * @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 buffer.    
 * @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    
 *    
 * <b>Coefficient and State Ordering:</b>    
 *    
 * \par    
 * 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>    
 * 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,
  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    
 */
