/* ----------------------------------------------------------------------  
* Copyright (C) 2010 ARM Limited. All rights reserved.  
*  
* $Date:        29. November 2010  
* $Revision: 	V1.0.3  
*  
* Project: 	    CMSIS DSP Library  
* Title:	    arm_fir_decimate_f32.c  
*  
* Description:	FIR decimation for floating-point sequences.  
*  
* 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 FIR_decimate Finite Impulse Response (FIR) Decimator  
 *  
 * These functions combine an FIR filter together with a decimator.  
 * They are used in multirate systems for reducing the sample rate of a signal without introducing aliasing distortion.  
 * Conceptually, the functions are equivalent to the block diagram below:  
 * \image html FIRDecimator.gif "Components included in the FIR Decimator functions"  
 * When decimating by a factor of <code>M</code>, the signal should be prefiltered by a lowpass filter with a normalized  
 * cutoff frequency of <code>1/M</code> in order to prevent aliasing distortion.  
 * The user of the function is responsible for providing the filter coefficients.  
 *  
 * The FIR decimator functions provided in the CMSIS DSP Library combine the FIR filter and the decimator in an efficient manner.  
 * Instead of calculating all of the FIR filter outputs and discarding <code>M-1</code> out of every <code>M</code>, only the  
 * samples output by the decimator are computed.  
 * The functions operate on blocks of input and output data.  
 * <code>pSrc</code> points to an array of <code>blockSize</code> input values and  
 * <code>pDst</code> points to an array of <code>blockSize/M</code> output values.  
 * In order to have an integer number of output samples <code>blockSize</code>  
 * must always be a multiple of the decimation factor <code>M</code>.  
 *  
 * The library provides separate functions for Q15, Q31 and floating-point data types.  
 *  
 * \par Algorithm:  
 * The FIR portion of the algorithm uses the standard form filter:  
 * <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>  
 * where, <code>b[n]</code> are the filter coefficients.  
 * \par 
 * The <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 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>  
 * 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 array should be allocated separately.  
 * 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.  
 * - Checks to make sure that the size of the input is a multiple of the decimation factor.  
 *  
 * \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.  
 * The code below statically initializes each of the 3 different data type filter instance structures  
 * <pre>  
 *arm_fir_decimate_instance_f32 S = {M, numTaps, pCoeffs, pState};  
 *arm_fir_decimate_instance_q31 S = {M, numTaps, pCoeffs, pState};  
 *arm_fir_decimate_instance_q15 S = {M, numTaps, pCoeffs, pState};  
 * </pre>  
 * where <code>M</code> is the decimation factor; <code>numTaps</code> is the number of filter coefficients in the filter;  
 * <code>pCoeffs</code> is the address of the coefficient buffer;  
 * <code>pState</code> is the address of the state buffer.  
 * Be sure to set the values in the state buffer to zeros when doing static initialization.  
 *  
 * \par Fixed-Point Behavior  
 * Care must be taken when using the fixed-point versions of the FIR decimate 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_decimate  
 * @{  
 */ 
 
  /**  
   * @brief Processing function for the floating-point FIR decimator.  
   * @param[in] *S        points to an instance of the floating-point FIR decimator 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 input samples to process per call.  
   * @return none.  
   */ 
 
void arm_fir_decimate_f32( 
  const arm_fir_decimate_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 sum0;                                /* Accumulator */ 
  float32_t x0, 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, outBlockSize = blockSize / S->M;  /* Loop counters */ 
 
  /* S->pState buffer contains previous frame (numTaps - 1) samples */ 
  /* pStateCurnt points to the location where the new input data should be written */ 
  pStateCurnt = S->pState + (numTaps - 1u); 
 
  /* Total number of output samples to be computed */ 
  blkCnt = outBlockSize; 
 
  while(blkCnt > 0u) 
  { 
    /* Copy decimation factor number of new input samples into the state buffer */ 
    i = S->M; 
 
    do 
    { 
      *pStateCurnt++ = *pSrc++; 
 
    } while(--i); 
 
    /* Set accumulator to zero */ 
    sum0 = 0.0f; 
 
    /* Initialize state pointer */ 
    px = pState; 
 
    /* Initialize coeff pointer */ 
    pb = pCoeffs; 
 
    /* Loop unrolling.  Process 4 taps at a time. */ 
    tapCnt = numTaps >> 2; 
 
    /* 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-1] sample */ 
      x0 = *(px++); 
 
      /* Perform the multiply-accumulate */ 
      sum0 += x0 * c0; 
 
      /* Read the b[numTaps-2] coefficient */ 
      c0 = *(pb++); 
 
      /* Read x[n-numTaps-2] sample */ 
      x0 = *(px++); 
 
      /* Perform the multiply-accumulate */ 
      sum0 += x0 * c0; 
 
      /* Read the b[numTaps-3] coefficient */ 
      c0 = *(pb++); 
 
      /* Read x[n-numTaps-3] sample */ 
      x0 = *(px++); 
 
      /* Perform the multiply-accumulate */ 
      sum0 += x0 * c0; 
 
      /* Read the b[numTaps-4] coefficient */ 
      c0 = *(pb++); 
 
      /* Read x[n-numTaps-4] sample */ 
      x0 = *(px++); 
 
      /* Perform the multiply-accumulate */ 
      sum0 += x0 * c0; 
 
      /* Decrement the loop counter */ 
      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 */ 
      x0 = *(px++); 
 
      /* Perform the multiply-accumulate */ 
      sum0 += x0 * c0; 
 
      /* Decrement the loop counter */ 
      tapCnt--; 
    } 
 
    /* Advance the state pointer by the decimation factor  
     * to process the next group of decimation factor number samples */ 
    pState = pState + S->M; 
 
    /* The result is in the accumulator, store in the destination buffer. */ 
    *pDst++ = sum0; 
 
    /* Decrement the loop counter */ 
    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; 
 
  i = (numTaps - 1u) >> 2; 
 
  /* copy data */ 
  while(i > 0u) 
  { 
    *pStateCurnt++ = *pState++; 
    *pStateCurnt++ = *pState++; 
    *pStateCurnt++ = *pState++; 
    *pStateCurnt++ = *pState++; 
 
    /* Decrement the loop counter */ 
    i--; 
  } 
 
  i = (numTaps - 1u) % 0x04u; 
 
  /* copy data */ 
  while(i > 0u) 
  { 
    *pStateCurnt++ = *pState++; 
 
    /* Decrement the loop counter */ 
    i--; 
  } 
} 
 
/**  
 * @} end of FIR_decimate group  
 */ 
