/* ----------------------------------------------------------------------  
* Copyright (C) 2010 ARM Limited. All rights reserved.  
*  
* $Date:        29. November 2010  
* $Revision: 	V1.0.3  
*  
* Project: 	    CMSIS DSP Library  
* Title:	    arm_iir_lattice_f32.c  
*  
* Description:	Floating-point IIR Lattice filter processing function.  
*  
* Target Processor: Cortex-M4/Cortex-M3
*  
* Version 1.0.3 2010/11/29 
*    Re-organized the CMSIS folders and updated documentation.  
*   
* Version 1.0.2 2010/11/11  
*    Documentation updated.   
*  
* Version 1.0.1 2010/10/05   
*    Production release and review comments incorporated.  
*  
* Version 1.0.0 2010/09/20   
*    Production release and review comments incorporated  
*  
* Version 0.0.7  2010/06/10   
*    Misra-C changes done  
* -------------------------------------------------------------------- */ 
 
#include "arm_math.h" 
 
/**  
 * @ingroup groupFilters  
 */ 
 
/**  
 * @defgroup IIR_Lattice Infinite Impulse Response (IIR) Lattice Filters  
 *  
 * This set of functions implements lattice filters  
 * for Q15, Q31 and floating-point data types.  Lattice filters are used in a   
 * variety of adaptive filter applications.  The filter structure has feedforward and  
 * feedback components and the net impulse response is infinite length.  
 * The functions operate on blocks  
 * of input and output data and each call to the function processes  
 * <code>blockSize</code> samples through the filter.  <code>pSrc</code> and  
 * <code>pDst</code> point to input and output arrays containing <code>blockSize</code> values.  
  
 * \par Algorithm:  
 * \image html IIRLattice.gif "Infinite Impulse Response Lattice filter"  
 * <pre>  
 *    fN(n)   =  x(n)  
 *    fm-1(n) = fm(n) - km * gm-1(n-1)   for m = N, N-1, ...1  
 *    gm(n)   = km * fm-1(n) + gm-1(n-1) for m = N, N-1, ...1  
 *    y(n)    = vN * gN(n) + vN-1 * gN-1(n) + ...+ v0 * g0(n)  
 * </pre>  
 * \par  
 * <code>pkCoeffs</code> points to array of reflection coefficients of size <code>numStages</code>.   
 * Reflection coefficients are stored in time-reversed order.  
 * \par  
 * <pre>  
 *    {kN, kN-1, ....k1}  
 * </pre>  
 * <code>pvCoeffs</code> points to the array of ladder coefficients of size <code>(numStages+1)</code>.   
 * Ladder coefficients are stored in time-reversed order.  
 * \par  
 * <pre>  
 *    {vN, vN-1, ...v0}  
 * </pre>  
 * <code>pState</code> points to a state array of size <code>numStages + blockSize</code>.  
 * The state variables shown in the figure above (the g values) are stored in the <code>pState</code> array.  
 * The state variables are updated after each block of data is processed; the coefficients are untouched.  
 * \par Instance Structure  
 * The coefficients and state variables for a filter are stored together in an instance data structure.  
 * A separate instance structure must be defined for each filter.  
 * Coefficient arrays may be shared among several instances while state variable arrays cannot be shared.  
 * There are separate instance structure declarations for each of the 3 supported data types.  
  *  
 * \par Initialization Functions  
 * There is also an associated initialization function for each data type.  
 * The initialization function performs the following operations:  
 * - Sets the values of the internal structure fields.  
 * - Zeros out the values in the state buffer.  
 *  
 * \par  
 * Use of the initialization function is optional.  
 * However, if the initialization function is used, then the instance structure cannot be placed into a const data section.  
 * To place an instance structure into a const data section, the instance structure must be manually initialized.  
 * Set the values in the state buffer to zeros and then manually initialize the instance structure as follows:  
 * <pre>  
 *arm_iir_lattice_instance_f32 S = {numStages, pState, pkCoeffs, pvCoeffs};  
 *arm_iir_lattice_instance_q31 S = {numStages, pState, pkCoeffs, pvCoeffs};  
 *arm_iir_lattice_instance_q15 S = {numStages, pState, pkCoeffs, pvCoeffs};  
 * </pre>  
 * \par  
 * where <code>numStages</code> is the number of stages in the filter; <code>pState</code> points to the state buffer array;  
 * <code>pkCoeffs</code> points to array of the reflection coefficients; <code>pvCoeffs</code> points to the array of ladder coefficients.  
 * \par Fixed-Point Behavior  
 * Care must be taken when using the fixed-point versions of the IIR lattice filter functions.  
 * In particular, the overflow and saturation behavior of the accumulator used in each function must be considered.  
 * Refer to the function specific documentation below for usage guidelines.  
 */ 
 
/**  
 * @addtogroup IIR_Lattice  
 * @{  
 */ 
 
/**  
 * @brief Processing function for the floating-point IIR lattice filter.  
 * @param[in] *S points to an instance of the floating-point IIR lattice structure.  
 * @param[in] *pSrc points to the block of input data.  
 * @param[out] *pDst points to the block of output data.  
 * @param[in] blockSize number of samples to process.  
 * @return none.  
 */ 
 
void arm_iir_lattice_f32( 
  const arm_iir_lattice_instance_f32 * S, 
  float32_t * pSrc, 
  float32_t * pDst, 
  uint32_t blockSize) 
{ 
  float32_t fcurr, fnext, gcurr, gnext;          /* Temporary variables for lattice stages */ 
  float32_t acc;                                 /* Accumlator */ 
  uint32_t blkCnt, tapCnt;                       /* temporary variables for counts */ 
  float32_t *px1, *px2, *pk, *pv;                /* temporary pointers for state and coef */ 
  uint32_t numStages = S->numStages;             /* number of stages */ 
  float32_t *pState;                             /* State pointer */ 
  float32_t *pStateCurnt;                        /* State current pointer */ 
 
  gcurr = 0.0f; 
  blkCnt = blockSize; 
 
  pState = &S->pState[0]; 
 
  /* Sample processing */ 
  while(blkCnt > 0u) 
  { 
    /* Read Sample from input buffer */ 
    /* fN(n) = x(n) */ 
    fcurr = *pSrc++; 
 
    /* Initialize state read pointer */ 
    px1 = pState; 
    /* Initialize state write pointer */ 
    px2 = pState; 
    /* Set accumulator to zero */ 
    acc = 0.0f; 
    /* Initialize Ladder coeff pointer */ 
    pv = &S->pvCoeffs[0]; 
    /* Initialize Reflection coeff pointer */ 
    pk = &S->pkCoeffs[0]; 
 
 
    /* Process sample for first tap */ 
    gcurr = *px1++; 
    /* fN-1(n) = fN(n) - kN * gN-1(n-1) */ 
    fnext = fcurr - ((*pk) * gcurr); 
    /* gN(n) = kN * fN-1(n) + gN-1(n-1) */ 
    gnext = (fnext * (*pk++)) + gcurr; 
    /* write gN(n) into state for next sample processing */ 
    *px2++ = gnext; 
    /* y(n) += gN(n) * vN  */ 
    acc += (gnext * (*pv++)); 
 
    /* Update f values for next coefficient processing */ 
    fcurr = fnext; 
 
    /* Loop unrolling.  Process 4 taps at a time. */ 
    tapCnt = (numStages - 1u) >> 2; 
 
    while(tapCnt > 0u) 
    { 
      /* Process sample for 2nd, 6th ...taps */ 
      /* Read gN-2(n-1) from state buffer */ 
      gcurr = *px1++; 
      /* Process sample for 2nd, 6th .. taps */ 
      /* fN-2(n) = fN-1(n) - kN-1 * gN-2(n-1) */ 
      fnext = fcurr - ((*pk) * gcurr); 
      /* gN-1(n) = kN-1 * fN-2(n) + gN-2(n-1) */ 
      gnext = (fnext * (*pk++)) + gcurr; 
      /* y(n) += gN-1(n) * vN-1  */ 
      /* process for gN-5(n) * vN-5, gN-9(n) * vN-9 ... */ 
      acc += (gnext * (*pv++)); 
      /* write gN-1(n) into state for next sample processing */ 
      *px2++ = gnext; 
 
 
      /* Process sample for 3nd, 7th ...taps */ 
      /* Read gN-3(n-1) from state buffer */ 
      gcurr = *px1++; 
      /* Process sample for 3rd, 7th .. taps */ 
      /* fN-3(n) = fN-2(n) - kN-2 * gN-3(n-1) */ 
      fcurr = fnext - ((*pk) * gcurr); 
      /* gN-2(n) = kN-2 * fN-3(n) + gN-3(n-1) */ 
      gnext = (fcurr * (*pk++)) + gcurr; 
      /* y(n) += gN-2(n) * vN-2  */ 
      /* process for gN-6(n) * vN-6, gN-10(n) * vN-10 ... */ 
      acc += (gnext * (*pv++)); 
      /* write gN-2(n) into state for next sample processing */ 
      *px2++ = gnext; 
 
 
      /* Process sample for 4th, 8th ...taps */ 
      /* Read gN-4(n-1) from state buffer */ 
      gcurr = *px1++; 
      /* Process sample for 4th, 8th .. taps */ 
      /* fN-4(n) = fN-3(n) - kN-3 * gN-4(n-1) */ 
      fnext = fcurr - ((*pk) * gcurr); 
      /* gN-3(n) = kN-3 * fN-4(n) + gN-4(n-1) */ 
      gnext = (fnext * (*pk++)) + gcurr; 
      /* y(n) += gN-3(n) * vN-3  */ 
      /* process for gN-7(n) * vN-7, gN-11(n) * vN-11 ... */ 
      acc += (gnext * (*pv++)); 
      /* write gN-3(n) into state for next sample processing */ 
      *px2++ = gnext; 
 
 
      /* Process sample for 5th, 9th ...taps */ 
      /* Read gN-5(n-1) from state buffer */ 
      gcurr = *px1++; 
      /* Process sample for 5th, 9th .. taps */ 
      /* fN-5(n) = fN-4(n) - kN-4 * gN-1(n-1) */ 
      fcurr = fnext - ((*pk) * gcurr); 
      /* gN-4(n) = kN-4 * fN-5(n) + gN-5(n-1) */ 
      gnext = (fcurr * (*pk++)) + gcurr; 
      /* y(n) += gN-4(n) * vN-4  */ 
      /* process for gN-8(n) * vN-8, gN-12(n) * vN-12 ... */ 
      acc += (gnext * (*pv++)); 
      /* write gN-4(n) into state for next sample processing */ 
      *px2++ = gnext; 
 
      tapCnt--; 
 
    } 
 
    fnext = fcurr; 
 
    /* If the filter length is not a multiple of 4, compute the remaining filter taps */ 
    tapCnt = (numStages - 1u) % 0x4u; 
 
    while(tapCnt > 0u) 
    { 
      gcurr = *px1++; 
      /* Process sample for last taps */ 
      fnext = fcurr - ((*pk) * gcurr); 
      gnext = (fnext * (*pk++)) + gcurr; 
      /* Output samples for last taps */ 
      acc += (gnext * (*pv++)); 
      *px2++ = gnext; 
      fcurr = fnext; 
 
      tapCnt--; 
 
    } 
 
 
    /* y(n) += g0(n) * v0 */ 
    acc += (fnext * (*pv)); 
 
    *px2++ = fnext; 
 
    /* write out into pDst */ 
    *pDst++ = acc; 
 
    /* Advance the state pointer by 4 to process the next group of 4 samples */ 
    pState = pState + 1u; 
    blkCnt--; 
 
  } 
 
  /* Processing is complete. Now copy last S->numStages samples to start of the buffer  
     for the preperation of next frame process */ 
 
  /* Points to the start of the state buffer */ 
  pStateCurnt = &S->pState[0]; 
  pState = &S->pState[blockSize]; 
 
  tapCnt = numStages >> 2u; 
 
  /* copy data */ 
  while(tapCnt > 0u) 
  { 
    *pStateCurnt++ = *pState++; 
    *pStateCurnt++ = *pState++; 
    *pStateCurnt++ = *pState++; 
    *pStateCurnt++ = *pState++; 
 
    /* Decrement the loop counter */ 
    tapCnt--; 
 
  } 
 
  /* Calculate remaining number of copies */ 
  tapCnt = (numStages) % 0x4u; 
 
  /* Copy the remaining q31_t data */ 
  while(tapCnt > 0u) 
  { 
    *pStateCurnt++ = *pState++; 
 
    /* Decrement the loop counter */ 
    tapCnt--; 
  } 
 
} 
 
 
 
 
/**  
 * @} end of IIR_Lattice group  
 */ 
