/* ----------------------------------------------------------------------  
* Copyright (C) 2010 ARM Limited. All rights reserved.  
*  
* $Date:        29. November 2010  
* $Revision: 	V1.0.3  
*  
* Project: 	    CMSIS DSP Library  
* Title:	    arm_fir_f32.c  
*  
* Description:	Floating-point FIR 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 0.0.5  2010/04/26   
* 	 incorporated review comments and updated with latest CMSIS layer  
*  
* Version 0.0.3  2010/03/10   
*    Initial version  
* -------------------------------------------------------------------- */ 
 
#include "arm_math.h" 
 
/**  
 * @ingroup groupFilters  
 */ 
 
/**  
 * @defgroup FIR Finite Impulse Response (FIR) Filters  
 *  
 * This set of functions implements Finite Impulse Response (FIR) filters  
 * for Q7, Q15, Q31, and floating-point data types.  Fast versions of Q15 and Q31 are also provided.  
 * 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> points to input and output arrays containing <code>blockSize</code> values.  
 *  
 * \par Algorithm:  
 * The FIR filter algorithm is based upon a sequence of multiply-accumulate (MAC) operations.  
 * Each filter coefficient <code>b[n]</code> is multiplied by a state variable which equals a previous input sample <code>x[n]</code>.  
 * <pre>  
 *    y[n] = b[0] * x[n] + b[1] * x[n-1] + b[2] * x[n-2] + ...+ b[numTaps-1] * x[n-numTaps+1]  
 * </pre>  
 * \par  
 * \image html FIR.gif "Finite Impulse Response filter"  
 * \par  
 * <code>pCoeffs</code> points to a coefficient array of size <code>numTaps</code>.  
 * Coefficients are stored in time reversed order.  
 * \par  
 * <pre>  
 *    {b[numTaps-1], b[numTaps-2], b[N-2], ..., b[1], b[0]}  
 * </pre>  
 * \par  
 * <code>pState</code> points to a state array of size <code>numTaps + blockSize - 1</code>.  
 * Samples in the state buffer are stored in the following order.  
 * \par  
 * <pre>  
 *    {x[n-numTaps+1], x[n-numTaps], x[n-numTaps-1], x[n-numTaps-2]....x[0], x[1], ..., x[blockSize-1]}  
 * </pre>  
 * \par  
 * Note that the length of the state buffer exceeds the length of the coefficient array by <code>blockSize-1</code>.  
 * The increased state buffer length allows circular addressing, which is traditionally used in the FIR filters,  
 * to be avoided and yields a significant speed improvement.  
 * 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 4 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 before static initialization.  
 * The code below statically initializes each of the 4 different data type filter instance structures  
 * <pre>  
 *arm_fir_instance_f32 S = {numTaps, pState, pCoeffs};  
 *arm_fir_instance_q31 S = {numTaps, pState, pCoeffs};  
 *arm_fir_instance_q15 S = {numTaps, pState, pCoeffs};  
 *arm_fir_instance_q7 S =  {numTaps, pState, pCoeffs};  
 * </pre>  
 *  
 * where <code>numTaps</code> is the number of filter coefficients in the filter; <code>pState</code> is the address of the state buffer;  
 * <code>pCoeffs</code> is the address of the coefficient buffer.  
 *  
 * \par Fixed-Point Behavior  
 * Care must be taken when using the fixed-point versions of the FIR 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 FIR  
 * @{  
 */ 
 
/**  
 *  
 * @param[in]  *S points to an instance of the floating-point FIR filter 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 per call.  
 * @return     none.  
 *  
 */ 
 
void arm_fir_f32( 
  const arm_fir_instance_f32 * S, 
  float32_t * pSrc, 
  float32_t * pDst, 
  uint32_t blockSize) 
{ 
  float32_t *pState = S->pState;                 /* State pointer */ 
  float32_t *pCoeffs = S->pCoeffs;               /* Coefficient pointer */ 
  float32_t *pStateCurnt;                        /* Points to the current sample of the state */ 
  float32_t *px, *pb;                            /* Temporary pointers for state and coefficient buffers */ 
  float32_t acc0, acc1, acc2, acc3;              /* Accumulators */ 
  float32_t x0, x1, x2, x3, c0;                  /* Temporary variables to hold state and coefficient values */ 
  uint32_t numTaps = S->numTaps;                 /* Number of filter coefficients in the filter */ 
  uint32_t i, tapCnt, blkCnt;                    /* Loop counters */ 
 
  /* S->pState points to state array which contains previous frame (numTaps - 1) samples */ 
  /* pStateCurnt points to the location where the new input data should be written */ 
  pStateCurnt = &(S->pState[(numTaps - 1u)]); 
 
  /* Apply loop unrolling and compute 4 output values simultaneously.  
   * The variables acc0 ... acc3 hold output values that are being computed:  
   *  
   *    acc0 =  b[numTaps-1] * x[n-numTaps-1] + b[numTaps-2] * x[n-numTaps-2] + b[numTaps-3] * x[n-numTaps-3] +...+ b[0] * x[0]  
   *    acc1 =  b[numTaps-1] * x[n-numTaps] +   b[numTaps-2] * x[n-numTaps-1] + b[numTaps-3] * x[n-numTaps-2] +...+ b[0] * x[1]  
   *    acc2 =  b[numTaps-1] * x[n-numTaps+1] + b[numTaps-2] * x[n-numTaps] +   b[numTaps-3] * x[n-numTaps-1] +...+ b[0] * x[2]  
   *    acc3 =  b[numTaps-1] * x[n-numTaps+2] + b[numTaps-2] * x[n-numTaps+1] + b[numTaps-3] * x[n-numTaps]   +...+ b[0] * x[3]  
   */ 
  blkCnt = blockSize >> 2; 
 
  /* First part of the processing with loop unrolling.  Compute 4 outputs at a time.  
   ** a second loop below computes the remaining 1 to 3 samples. */ 
  while(blkCnt > 0u) 
  { 
    /* Copy four new input samples into the state buffer */ 
    *pStateCurnt++ = *pSrc++; 
    *pStateCurnt++ = *pSrc++; 
    *pStateCurnt++ = *pSrc++; 
    *pStateCurnt++ = *pSrc++; 
 
    /* Set all accumulators to zero */ 
    acc0 = 0.0f; 
    acc1 = 0.0f; 
    acc2 = 0.0f; 
    acc3 = 0.0f; 
 
    /* Initialize state pointer */ 
    px = pState; 
 
    /* Initialize coeff pointer */ 
    pb = (pCoeffs); 
 
    /* Read the first three samples from the state buffer:  x[n-numTaps], x[n-numTaps-1], x[n-numTaps-2] */ 
    x0 = *px++; 
    x1 = *px++; 
    x2 = *px++; 
 
    /* Loop unrolling.  Process 4 taps at a time. */ 
    tapCnt = numTaps >> 2u; 
 
    /* Loop over the number of taps.  Unroll by a factor of 4.  
     ** Repeat until we've computed numTaps-4 coefficients. */ 
    while(tapCnt > 0u) 
    { 
      /* Read the b[numTaps-1] coefficient */ 
      c0 = *(pb++); 
 
      /* Read x[n-numTaps-3] sample */ 
      x3 = *(px++); 
 
      /* acc0 +=  b[numTaps-1] * x[n-numTaps] */ 
      acc0 += x0 * c0; 
 
      /* acc1 +=  b[numTaps-1] * x[n-numTaps-1] */ 
      acc1 += x1 * c0; 
 
      /* acc2 +=  b[numTaps-1] * x[n-numTaps-2] */ 
      acc2 += x2 * c0; 
 
      /* acc3 +=  b[numTaps-1] * x[n-numTaps-3] */ 
      acc3 += x3 * c0; 
 
      /* Read the b[numTaps-2] coefficient */ 
      c0 = *(pb++); 
 
      /* Read x[n-numTaps-4] sample */ 
      x0 = *(px++); 
 
      /* Perform the multiply-accumulate */ 
      acc0 += x1 * c0; 
      acc1 += x2 * c0; 
      acc2 += x3 * c0; 
      acc3 += x0 * c0; 
 
      /* Read the b[numTaps-3] coefficient */ 
      c0 = *(pb++); 
 
      /* Read x[n-numTaps-5] sample */ 
      x1 = *(px++); 
 
      /* Perform the multiply-accumulates */ 
      acc0 += x2 * c0; 
      acc1 += x3 * c0; 
      acc2 += x0 * c0; 
      acc3 += x1 * c0; 
 
      /* Read the b[numTaps-4] coefficient */ 
      c0 = *(pb++); 
 
      /* Read x[n-numTaps-6] sample */ 
      x2 = *(px++); 
 
      /* Perform the multiply-accumulates */ 
      acc0 += x3 * c0; 
      acc1 += x0 * c0; 
      acc2 += x1 * c0; 
      acc3 += x2 * c0; 
 
      tapCnt--; 
    } 
 
    /* If the filter length is not a multiple of 4, compute the remaining filter taps */ 
    tapCnt = numTaps % 0x4u; 
 
    while(tapCnt > 0u) 
    { 
      /* Read coefficients */ 
      c0 = *(pb++); 
 
      /* Fetch 1 state variable */ 
      x3 = *(px++); 
 
      /* Perform the multiply-accumulates */ 
      acc0 += x0 * c0; 
      acc1 += x1 * c0; 
      acc2 += x2 * c0; 
      acc3 += x3 * c0; 
 
      /* Reuse the present sample states for next sample */ 
      x0 = x1; 
      x1 = x2; 
      x2 = x3; 
 
      /* Decrement the loop counter */ 
      tapCnt--; 
    } 
 
    /* Advance the state pointer by 4 to process the next group of 4 samples */ 
    pState = pState + 4; 
 
    /* The results in the 4 accumulators, store in the destination buffer. */ 
    *pDst++ = acc0; 
    *pDst++ = acc1; 
    *pDst++ = acc2; 
    *pDst++ = acc3; 
 
    blkCnt--; 
  } 
 
  /* If the blockSize is not a multiple of 4, compute any remaining output samples here.  
   ** No loop unrolling is used. */ 
  blkCnt = blockSize % 0x4u; 
 
  while(blkCnt > 0u) 
  { 
    /* Copy one sample at a time into state buffer */ 
    *pStateCurnt++ = *pSrc++; 
 
    /* Set the accumulator to zero */ 
    acc0 = 0.0f; 
 
    /* Initialize state pointer */ 
    px = pState; 
 
    /* Initialize Coefficient pointer */ 
    pb = (pCoeffs); 
 
    i = numTaps; 
 
    /* Perform the multiply-accumulates */ 
    do 
    { 
      acc0 += *px++ * *pb++; 
      i--; 
 
    } while(i > 0u); 
 
    /* The result is store in the destination buffer. */ 
    *pDst++ = acc0; 
 
    /* Advance state pointer by 1 for the next sample */ 
    pState = pState + 1; 
 
    blkCnt--; 
  } 
 
  /* Processing is complete.  
   ** Now copy the last numTaps - 1 samples to the satrt of the state buffer.  
   ** This prepares the state buffer for the next function call. */ 
 
  /* Points to the start of the state buffer */ 
  pStateCurnt = S->pState; 
 
  tapCnt = (numTaps - 1u) >> 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 = (numTaps - 1u) % 0x4u; 
 
  /* Copy the remaining q31_t data */ 
  while(tapCnt > 0u) 
  { 
    *pStateCurnt++ = *pState++; 
 
    /* Decrement the loop counter */ 
    tapCnt--; 
  } 
} 
 
/**  
 * @} end of FIR group  
 */ 
