text: /* ----------------------------------------------------------------------
   * Project:      CMSIS DSP Library
   * Title:        arm_fir_interpolate_f32.c
   * Description:  Floating-point FIR interpolation sequences
   *
   * $Date:        27. January 2017
   * $Revision:    V.1.5.1
   *
   * Target Processor: Cortex-M cores
   * -------------------------------------------------------------------- */
  /*
   * Copyright (C) 2010-2017 ARM Limited or its affiliates. All rights reserved.
   *
   * SPDX-License-Identifier: Apache-2.0
   *
   * Licensed under the Apache License, Version 2.0 (the License); you may
   * not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   * www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an AS IS BASIS, WITHOUT
   * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  #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.
   * To do this manually without calling the init function, assign the follow subfields of the instance structure:
   * L (interpolation factor), pCoeffs, phaseLength (numTaps / L), pState. Also set all of the values in pState to zero.
   *
   * \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.
   */
  #if defined (ARM_MATH_DSP)
  
    /* Run the below code for Cortex-M4 and Cortex-M3 */
  
  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 */
    float32_t acc0, acc1, acc2, acc3;
    float32_t x1, x2, x3;
    uint32_t blkCntN4;
    float32_t c1, c2, c3;
  
    /* 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);
  
    /* Initialise  blkCnt */
    blkCnt = blockSize / 4;
    blkCntN4 = blockSize - (4 * blkCnt);
  
    /* Samples loop unrolled by 4 */
    while (blkCnt > 0U)
    {
      /* Copy new input sample into the state buffer */
      *pStateCurnt++ = *pSrc++;
      *pStateCurnt++ = *pSrc++;
      *pStateCurnt++ = *pSrc++;
      *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 */
        acc0 = 0.0f;
        acc1 = 0.0f;
        acc2 = 0.0f;
        acc3 = 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;
  
        x0 = *(ptr1++);
        x1 = *(ptr1++);
        x2 = *(ptr1++);
  
        while (tapCnt > 0U)
        {
  
          /* Read the input sample */
          x3 = *(ptr1++);
  
          /* Read the coefficient */
          c0 = *(ptr2);
  
          /* Perform the multiply-accumulate */
          acc0 += x0 * c0;
          acc1 += x1 * c0;
          acc2 += x2 * c0;
          acc3 += x3 * c0;
  
          /* Read the coefficient */
          c1 = *(ptr2 + S->L);
  
          /* Read the input sample */
          x0 = *(ptr1++);
  
          /* Perform the multiply-accumulate */
          acc0 += x1 * c1;
          acc1 += x2 * c1;
          acc2 += x3 * c1;
          acc3 += x0 * c1;
  
          /* Read the coefficient */
          c2 = *(ptr2 + S->L * 2);
  
          /* Read the input sample */
          x1 = *(ptr1++);
  
          /* Perform the multiply-accumulate */
          acc0 += x2 * c2;
          acc1 += x3 * c2;
          acc2 += x0 * c2;
          acc3 += x1 * c2;
  
          /* Read the coefficient */
          c3 = *(ptr2 + S->L * 3);
  
          /* Read the input sample */
          x2 = *(ptr1++);
  
          /* Perform the multiply-accumulate */
          acc0 += x3 * c3;
          acc1 += x0 * c3;
          acc2 += x1 * c3;
          acc3 += x2 * c3;
  
  
          /* 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 += 4 * S->L;
  
          /* 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)
        {
  
          /* Read the input sample */
          x3 = *(ptr1++);
  
          /* Read the coefficient */
          c0 = *(ptr2);
  
          /* Perform the multiply-accumulate */
          acc0 += x0 * c0;
          acc1 += x1 * c0;
          acc2 += x2 * c0;
          acc3 += x3 * c0;
  
          /* Increment the coefficient pointer by interpolation factor times. */
          ptr2 += S->L;
  
          /* update states for next sample processing */
          x0 = x1;
          x1 = x2;
          x2 = x3;
  
          /* Decrement the loop counter */
          tapCnt--;
        }
  
        /* The result is in the accumulator, store in the destination buffer. */
        *pDst = acc0;
        *(pDst + S->L) = acc1;
        *(pDst + 2 * S->L) = acc2;
        *(pDst + 3 * S->L) = acc3;
  
        pDst++;
  
        /* 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 + 4;
  
      pDst += S->L * 3;
  
      /* Decrement the loop counter */
      blkCnt--;
    }
  
    /* If the blockSize is not a multiple of 4, compute any remaining output samples here.
     ** No loop unrolling is used. */
  
    while (blkCntN4 > 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 */
      blkCntN4--;
    }
  
    /* 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;
  
    /* copy data */
    while (tapCnt > 0U)
    {
      *pStateCurnt++ = *pState++;
  
      /* Decrement the loop counter */
      tapCnt--;
    }
  }
  
  #else
  
    /* Run the below code for Cortex-M0 */
  
  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 sum;                                 /* Accumulator */
    uint32_t i, blkCnt;                            /* 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++;
  
      /* Loop over the Interpolation factor. */
      i = S->L;
  
      while (i > 0U)
      {
        /* Set accumulator to zero */
        sum = 0.0f;
  
        /* Initialize state pointer */
        ptr1 = pState;
  
        /* Initialize coefficient pointer */
        ptr2 = pCoeffs + (i - 1U);
  
        /* Loop over the polyPhase length */
        tapCnt = phaseLen;
  
        while (tapCnt > 0U)
        {
          /* Perform the multiply-accumulate */
          sum += *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++ = sum;
  
        /* 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;
  
    tapCnt = phaseLen - 1U;
  
    while (tapCnt > 0U)
    {
      *pStateCurnt++ = *pState++;
  
      /* Decrement the loop counter */
      tapCnt--;
    }
  
  }
  
  #endif /*   #if defined (ARM_MATH_DSP) */
  
  
  
   /**
    * @} end of FIR_Interpolate group
    */
  