/* ----------------------------------------------------------------------  
* Copyright (C) 2010 ARM Limited. All rights reserved.  
*  
* $Date:        29. November 2010  
* $Revision: 	V1.0.3  
*  
* Project: 	    CMSIS DSP Library  
* Title:	    arm_fir_interpolate_f32.c  
*  
* Description:	FIR interpolation 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" 
 
/**  
 * @defgroup FIR_Interpolate Finite Impulse Response (FIR) Interpolator  
 *  
 * These functions combine an upsampler (zero stuffer) and an FIR filter.  
 * They are used in multirate systems for increasing the sample rate of a signal without introducing high frequency images.  
 * Conceptually, the functions are equivalent to the block diagram below:  
 * \image html FIRInterpolator.gif "Components included in the FIR Interpolator functions"  
 * After upsampling by a factor of <code>L</code>, the signal should be filtered by a lowpass filter with a normalized  
 * cutoff frequency of <code>1/L</code> in order to eliminate high frequency copies of the spectrum.  
 * The user of the function is responsible for providing the filter coefficients.  
 *  
 * The FIR interpolator functions provided in the CMSIS DSP Library combine the upsampler and FIR filter in an efficient manner.  
 * The upsampler inserts <code>L-1</code> zeros between each sample.  
 * Instead of multiplying by these zero values, the FIR filter is designed to skip them.  
 * This leads to an efficient implementation without any wasted effort.  
 * 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*L</code> output values.  
 *  
 * The library provides separate functions for Q15, Q31, and floating-point data types.  
 *  
 * \par Algorithm:  
 * The functions use a polyphase filter structure:  
 * <pre>  
 *    y[n] = b[0] * x[n] + b[L]   * x[n-1] + ... + b[L*(phaseLength-1)] * x[n-phaseLength+1]  
 *    y[n+1] = b[1] * x[n] + b[L+1] * x[n-1] + ... + b[L*(phaseLength-1)+1] * x[n-phaseLength+1]  
 *    ...  
 *    y[n+(L-1)] = b[L-1] * x[n] + b[2*L-1] * x[n-1] + ....+ b[L*(phaseLength-1)+(L-1)] * x[n-phaseLength+1]  
 * </pre>  
 * This approach is more efficient than straightforward upsample-then-filter algorithms.  
 * With this method the computation is reduced by a factor of <code>1/L</code> when compared to using a standard FIR filter.  
 * \par  
 * <code>pCoeffs</code> points to a coefficient array of size <code>numTaps</code>.  
 * <code>numTaps</code> must be a multiple of the interpolation factor <code>L</code> and this is checked by the  
 * initialization functions.  
 * Internally, the function divides the FIR filter's impulse response into shorter filters of length  
 * <code>phaseLength=numTaps/L</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>blockSize + phaseLength - 1</code>.  
 * Samples in the state buffer are stored in the order:  
 * \par  
 * <pre>  
 *    {x[n-phaseLength+1], x[n-phaseLength], x[n-phaseLength-1], x[n-phaseLength-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 length of the filter is a multiple of the interpolation 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_interpolate_instance_f32 S = {L, phaseLength, pCoeffs, pState};  
 * arm_fir_interpolate_instance_q31 S = {L, phaseLength, pCoeffs, pState};  
 * arm_fir_interpolate_instance_q15 S = {L, phaseLength, pCoeffs, pState};  
 * </pre>  
 * where <code>L</code> is the interpolation factor; <code>phaseLength=numTaps/L</code> is the  
 * length of each of the shorter FIR filters used internally,  
 * <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 interpolate 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_Interpolate  
 * @{  
 */ 
 
/**  
 * @brief Processing function for the floating-point FIR interpolator.  
 * @param[in] *S        points to an instance of the floating-point FIR interpolator 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_interpolate_f32( 
  const arm_fir_interpolate_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 *ptr1, *ptr2;                        /* Temporary pointers for state and coefficient buffers */ 
  float32_t sum0;                                /* Accumulators */ 
  float32_t x0, c0;                              /* Temporary variables to hold state and coefficient values */ 
  uint32_t i, blkCnt, j;                         /* Loop counters */ 
  uint16_t phaseLen = S->phaseLength, tapCnt;    /* Length of each polyphase filter component */ 
 
 
  /* S->pState buffer contains previous frame (phaseLen - 1) samples */ 
  /* pStateCurnt points to the location where the new input data should be written */ 
  pStateCurnt = S->pState + (phaseLen - 1u); 
 
  /* Total number of intput samples */ 
  blkCnt = blockSize; 
 
  /* Loop over the blockSize. */ 
  while(blkCnt > 0u) 
  { 
    /* Copy new input sample into the state buffer */ 
    *pStateCurnt++ = *pSrc++; 
 
    /* Address modifier index of coefficient buffer */ 
    j = 1u; 
 
    /* Loop over the Interpolation factor. */ 
    i = S->L; 
    while(i > 0u) 
    { 
      /* Set accumulator to zero */ 
      sum0 = 0.0f; 
 
      /* Initialize state pointer */ 
      ptr1 = pState; 
 
      /* Initialize coefficient pointer */ 
      ptr2 = pCoeffs + (S->L - j); 
 
      /* Loop over the polyPhase length. Unroll by a factor of 4.  
       ** Repeat until we've computed numTaps-(4*S->L) coefficients. */ 
      tapCnt = phaseLen >> 2u; 
      while(tapCnt > 0u) 
      { 
 
        /* Read the coefficient */ 
        c0 = *(ptr2); 
 
        /* Upsampling is done by stuffing L-1 zeros between each sample.  
         * So instead of multiplying zeros with coefficients,  
         * Increment the coefficient pointer by interpolation factor times. */ 
        ptr2 += S->L; 
 
        /* Read the input sample */ 
        x0 = *(ptr1++); 
 
        /* Perform the multiply-accumulate */ 
        sum0 += x0 * c0; 
 
        /* Read the coefficient */ 
        c0 = *(ptr2); 
 
        /* Increment the coefficient pointer by interpolation factor times. */ 
        ptr2 += S->L; 
 
        /* Read the input sample */ 
        x0 = *(ptr1++); 
 
        /* Perform the multiply-accumulate */ 
        sum0 += x0 * c0; 
 
        /* Read the coefficient */ 
        c0 = *(ptr2); 
 
        /* Increment the coefficient pointer by interpolation factor times. */ 
        ptr2 += S->L; 
 
        /* Read the input sample */ 
        x0 = *(ptr1++); 
 
        /* Perform the multiply-accumulate */ 
        sum0 += x0 * c0; 
 
        /* Read the coefficient */ 
        c0 = *(ptr2); 
 
        /* Increment the coefficient pointer by interpolation factor times. */ 
        ptr2 += S->L; 
 
        /* Read the input sample */ 
        x0 = *(ptr1++); 
 
        /* Perform the multiply-accumulate */ 
        sum0 += x0 * c0; 
 
        /* Decrement the loop counter */ 
        tapCnt--; 
      } 
 
      /* If the polyPhase length is not a multiple of 4, compute the remaining filter taps */ 
      tapCnt = phaseLen % 0x4u; 
 
      while(tapCnt > 0u) 
      { 
        /* Perform the multiply-accumulate */ 
        sum0 += *(ptr1++) * (*ptr2); 
 
        /* Increment the coefficient pointer by interpolation factor times. */ 
        ptr2 += S->L; 
 
        /* Decrement the loop counter */ 
        tapCnt--; 
      } 
 
      /* The result is in the accumulator, store in the destination buffer. */ 
      *pDst++ = sum0; 
 
      /* Increment the address modifier index of coefficient buffer */ 
      j++; 
 
      /* Decrement the loop counter */ 
      i--; 
    } 
 
    /* Advance the state pointer by 1  
     * to process the next group of interpolation factor number samples */ 
    pState = pState + 1; 
 
    /* Decrement the loop counter */ 
    blkCnt--; 
  } 
 
  /* Processing is complete.  
   ** Now copy the last phaseLen - 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 = (phaseLen - 1u) >> 2u; 
 
  /* copy data */ 
  while(tapCnt > 0u) 
  { 
    *pStateCurnt++ = *pState++; 
    *pStateCurnt++ = *pState++; 
    *pStateCurnt++ = *pState++; 
    *pStateCurnt++ = *pState++; 
 
    /* Decrement the loop counter */ 
    tapCnt--; 
  } 
 
  tapCnt = (phaseLen - 1u) % 0x04u; 
 
  while(tapCnt > 0u) 
  { 
    *pStateCurnt++ = *pState++; 
 
    /* Decrement the loop counter */ 
    tapCnt--; 
  } 
} 
 
 /**  
  * @} end of FIR_Interpolate group  
  */ 
