hardware/arduino/sam/system/CMSIS/CMSIS/DSP_Lib/Source/FilteringFunctions/arm_fir_interpolate_q15.c

/*-----------------------------------------------------------------------------   
* Copyright (C) 2010 ARM Limited. All rights reserved.   
*   
* $Date:        15. July 2011  
* $Revision: 	V1.0.10  
*   
* Project: 	    CMSIS DSP Library   
* Title:		arm_fir_interpolate_q15.c   
*   
* Description:	Q15 FIR interpolation.   
*   
* Target Processor: Cortex-M4/Cortex-M3/Cortex-M0
*  
* Version 1.0.10 2011/7/15 
*    Big Endian support added and Merged M0 and M3/M4 Source code.  
*   
* 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   
 */

/**   
 * @addtogroup FIR_Interpolate   
 * @{   
 */

/**   
 * @brief Processing function for the Q15 FIR interpolator.   
 * @param[in] *S        points to an instance of the Q15 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.   
 *   
 * <b>Scaling and Overflow Behavior:</b>   
 * \par   
 * The function is implemented using a 64-bit internal accumulator.   
 * Both coefficients and state variables are represented in 1.15 format and multiplications yield a 2.30 result.   
 * The 2.30 intermediate results are accumulated in a 64-bit accumulator in 34.30 format.   
 * There is no risk of internal overflow with this approach and the full precision of intermediate multiplications is preserved.   
 * After all additions have been performed, the accumulator is truncated to 34.15 format by discarding low 15 bits.   
 * Lastly, the accumulator is saturated to yield a result in 1.15 format.   
 */

void arm_fir_interpolate_q15(
  const arm_fir_interpolate_instance_q15 * S,
  q15_t * pSrc,
  q15_t * pDst,
  uint32_t blockSize)
{
  q15_t *pState = S->pState;                     /* State pointer                                            */
  q15_t *pCoeffs = S->pCoeffs;                   /* Coefficient pointer                                      */
  q15_t *pStateCurnt;                            /* Points to the current sample of the state                */
  q15_t *ptr1, *ptr2;                            /* Temporary pointers for state and coefficient buffers     */


#ifndef ARM_MATH_CM0

  /* Run the below code for Cortex-M4 and Cortex-M3 */

  q63_t sum0;                                    /* Accumulators                                             */
  q15_t x0, c0, c1;                              /* Temporary variables to hold state and coefficient values */
  q31_t c, x;
  uint32_t i, blkCnt, j, tapCnt;                 /* Loop counters                                            */
  uint16_t phaseLen = S->phaseLength;            /* 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;

      /* 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 = (uint32_t) 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 coefficient */
        c1 = *(ptr2);

        /* Increment the coefficient pointer by interpolation factor times. */
        ptr2 += S->L;

        /* Pack the coefficients */
#ifndef  ARM_MATH_BIG_ENDIAN

        c = __PKHBT(c0, c1, 16);

#else

        c = __PKHBT(c1, c0, 16);

#endif /*      #ifndef  ARM_MATH_BIG_ENDIAN    */

        /* Read twp consecutive input samples */
        x = *__SIMD32(ptr1)++;

        /* Perform the multiply-accumulate */
        sum0 = __SMLALD(x, c, sum0);

        /* Read the coefficient */
        c0 = *(ptr2);

        /* Upsampling is done by stuffing L-1 zeros between each sample.   
         * So insted of multiplying zeros with coefficients,   
         * Increment the coefficient pointer by interpolation factor times. */
        ptr2 += S->L;

        /* Read the coefficient */
        c1 = *(ptr2);

        /* Increment the coefficient pointer by interpolation factor times. */
        ptr2 += S->L;

        /* Pack the coefficients */
#ifndef  ARM_MATH_BIG_ENDIAN

        c = __PKHBT(c0, c1, 16);

#else

        c = __PKHBT(c1, c0, 16);

#endif /*      #ifndef  ARM_MATH_BIG_ENDIAN            */

        /* Read twp consecutive input samples */
        x = *__SIMD32(ptr1)++;

        /* Perform the multiply-accumulate */
        sum0 = __SMLALD(x, c, sum0);

        /* Decrement the loop counter */
        tapCnt--;
      }

      /* If the polyPhase length is not a multiple of 4, compute the remaining filter taps */
      tapCnt = (uint32_t) phaseLen & 0x3u;

      while(tapCnt > 0u)
      {
        /* 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 = __SMLALD(x0, c0, sum0);

        /* Decrement the loop counter */
        tapCnt--;
      }

      /* The result is in the accumulator, store in the destination buffer. */
      *pDst++ = (q15_t) (__SSAT((sum0 >> 15), 16));

      /* 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;

  i = ((uint32_t) phaseLen - 1u) >> 2u;

  /* copy data */
  while(i > 0u)
  {
    *__SIMD32(pStateCurnt)++ = *__SIMD32(pState)++;
    *__SIMD32(pStateCurnt)++ = *__SIMD32(pState)++;

    /* Decrement the loop counter */
    i--;
  }

  i = ((uint32_t) phaseLen - 1u) % 0x04u;

  while(i > 0u)
  {
    *pStateCurnt++ = *pState++;

    /* Decrement the loop counter */
    i--;
  }

#else

  /* Run the below code for Cortex-M0 */

  q63_t sum;                                     /* Accumulator */
  q15_t x0, c0;                                  /* Temporary variables to hold state and coefficient values */
  uint32_t i, blkCnt, tapCnt;                    /* Loop counters                                            */
  uint16_t phaseLen = S->phaseLength;            /* 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++;

    /* Loop over the Interpolation factor. */
    i = S->L;

    while(i > 0u)
    {
      /* Set accumulator to zero */
      sum = 0;

      /* Initialize state pointer */
      ptr1 = pState;

      /* Initialize coefficient pointer */
      ptr2 = pCoeffs + (i - 1u);

      /* Loop over the polyPhase length */
      tapCnt = (uint32_t) phaseLen;

      while(tapCnt > 0u)
      {
        /* 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 */
        sum += ((q31_t) x0 * c0);

        /* Decrement the loop counter */
        tapCnt--;
      }

      /* Store the result after converting to 1.15 format in the destination buffer */
      *pDst++ = (q15_t) (__SSAT((sum >> 15), 16));

      /* 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 start 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 = (uint32_t) phaseLen - 1u;

  while(i > 0u)
  {
    *pStateCurnt++ = *pState++;

    /* Decrement the loop counter */
    i--;
  }

#endif /*   #ifndef ARM_MATH_CM0 */

}

 /**   
  * @} end of FIR_Interpolate group   
  */