CMSIS_5/CMSIS/DSP/Source/TransformFunctions/arm_rfft_f32.c

/* ----------------------------------------------------------------------
 * Project:      CMSIS DSP Library
 * Title:        arm_rfft_f32.c
 * Description:  RFFT & RIFFT Floating point process function
 *
 * $Date:        18. March 2019
 * $Revision:    V1.6.0
 *
 * Target Processor: Cortex-M cores
 * -------------------------------------------------------------------- */
/*
 * Copyright (C) 2010-2019 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"

/* ----------------------------------------------------------------------
 * Internal functions prototypes
 * -------------------------------------------------------------------- */

extern void arm_radix4_butterfly_f32(
        float32_t * pSrc,
        uint16_t fftLen,
  const float32_t * pCoef,
        uint16_t twidCoefModifier);

extern void arm_radix4_butterfly_inverse_f32(
        float32_t * pSrc,
        uint16_t fftLen,
  const float32_t * pCoef,
        uint16_t twidCoefModifier,
        float32_t onebyfftLen);

extern void arm_bitreversal_f32(
        float32_t * pSrc,
        uint16_t fftSize,
        uint16_t bitRevFactor,
  const uint16_t * pBitRevTab);

void arm_split_rfft_f32(
        float32_t * pSrc,
        uint32_t fftLen,
  const float32_t * pATable,
  const float32_t * pBTable,
        float32_t * pDst,
        uint32_t modifier);

void arm_split_rifft_f32(
        float32_t * pSrc,
        uint32_t fftLen,
  const float32_t * pATable,
  const float32_t * pBTable,
        float32_t * pDst,
        uint32_t modifier);

/**
  @ingroup groupTransforms
 */

/**
  @addtogroup RealFFT
  @{
 */

/**
  @brief         Processing function for the floating-point RFFT/RIFFT.
                 Source buffer is modified by this function.
                 
  @deprecated    Do not use this function.  It has been superceded by \ref arm_rfft_fast_f32 and will be removed in the future.
  @param[in]     S    points to an instance of the floating-point RFFT/RIFFT structure
  @param[in]     pSrc points to the input buffer
  @param[out]    pDst points to the output buffer
  @return        none
 */

void arm_rfft_f32(
  const arm_rfft_instance_f32 * S,
        float32_t * pSrc,
        float32_t * pDst)
{
  const arm_cfft_radix4_instance_f32 *S_CFFT = S->pCfft;

  /* Calculation of Real IFFT of input */
  if (S->ifftFlagR == 1U)
  {
     /*  Real IFFT core process */
     arm_split_rifft_f32 (pSrc, S->fftLenBy2, S->pTwiddleAReal, S->pTwiddleBReal, pDst, S->twidCoefRModifier);


     /* Complex radix-4 IFFT process */
     arm_radix4_butterfly_inverse_f32 (pDst, S_CFFT->fftLen, S_CFFT->pTwiddle, S_CFFT->twidCoefModifier, S_CFFT->onebyfftLen);

    /* Bit reversal process */
    if (S->bitReverseFlagR == 1U)
    {
      arm_bitreversal_f32 (pDst, S_CFFT->fftLen, S_CFFT->bitRevFactor, S_CFFT->pBitRevTable);
    }
  }
  else
  {
    /* Calculation of RFFT of input */

    /* Complex radix-4 FFT process */
    arm_radix4_butterfly_f32 (pSrc, S_CFFT->fftLen, S_CFFT->pTwiddle, S_CFFT->twidCoefModifier);

    /* Bit reversal process */
    if (S->bitReverseFlagR == 1U)
    {
      arm_bitreversal_f32 (pSrc, S_CFFT->fftLen, S_CFFT->bitRevFactor, S_CFFT->pBitRevTable);
    }

    /*  Real FFT core process */
    arm_split_rfft_f32 (pSrc, S->fftLenBy2, S->pTwiddleAReal, S->pTwiddleBReal, pDst, S->twidCoefRModifier);
  }

}

/**
  @} end of RealFFT group
 */

/**
  @brief         Core Real FFT process
  @param[in]     pSrc      points to input buffer
  @param[in]     fftLen    length of FFT
  @param[in]     pATable   points to twiddle Coef A buffer
  @param[in]     pBTable   points to twiddle Coef B buffer
  @param[out]    pDst      points to output buffer
  @param[in]     modifier  twiddle coefficient modifier that supports different size FFTs with the same twiddle factor table
  @return        none
 */

void arm_split_rfft_f32(
        float32_t * pSrc,
        uint32_t fftLen,
  const float32_t * pATable,
  const float32_t * pBTable,
        float32_t * pDst,
        uint32_t modifier)
{
        uint32_t i;                                    /* Loop Counter */
        float32_t outR, outI;                          /* Temporary variables for output */
  const float32_t *pCoefA, *pCoefB;                    /* Temporary pointers for twiddle factors */
        float32_t CoefA1, CoefA2, CoefB1;              /* Temporary variables for twiddle coefficients */
        float32_t *pDst1 = &pDst[2], *pDst2 = &pDst[(4U * fftLen) - 1U];      /* temp pointers for output buffer */
        float32_t *pSrc1 = &pSrc[2], *pSrc2 = &pSrc[(2U * fftLen) - 1U];      /* temp pointers for input buffer */

  /* Init coefficient pointers */
  pCoefA = &pATable[modifier * 2];
  pCoefB = &pBTable[modifier * 2];

  i = fftLen - 1U;

  while (i > 0U)
  {
     /*
       outR = (  pSrc[2 * i]             * pATable[2 * i]
               - pSrc[2 * i + 1]         * pATable[2 * i + 1]
               + pSrc[2 * n - 2 * i]     * pBTable[2 * i]
               + pSrc[2 * n - 2 * i + 1] * pBTable[2 * i + 1]);

       outI = (  pIn[2 * i + 1]         * pATable[2 * i]
               + pIn[2 * i]             * pATable[2 * i + 1]
               + pIn[2 * n - 2 * i]     * pBTable[2 * i + 1]
               - pIn[2 * n - 2 * i + 1] * pBTable[2 * i]);
      */

    /* read pATable[2 * i] */
    CoefA1 = *pCoefA++;
    /* pATable[2 * i + 1] */
    CoefA2 = *pCoefA;

    /* pSrc[2 * i] * pATable[2 * i] */
    outR = *pSrc1 * CoefA1;
    /* pSrc[2 * i] * CoefA2 */
    outI = *pSrc1++ * CoefA2;

    /* (pSrc[2 * i + 1] + pSrc[2 * fftLen - 2 * i + 1]) * CoefA2 */
    outR -= (*pSrc1 + *pSrc2) * CoefA2;
    /* pSrc[2 * i + 1] * CoefA1 */
    outI += *pSrc1++ * CoefA1;

    CoefB1 = *pCoefB;

    /* pSrc[2 * fftLen - 2 * i + 1] * CoefB1 */
    outI -= *pSrc2-- * CoefB1;
    /* pSrc[2 * fftLen - 2 * i] * CoefA2 */
    outI -= *pSrc2 * CoefA2;

    /* pSrc[2 * fftLen - 2 * i] * CoefB1 */
    outR += *pSrc2-- * CoefB1;

    /* write output */
    *pDst1++ = outR;
    *pDst1++ = outI;

    /* write complex conjugate output */
    *pDst2-- = -outI;
    *pDst2-- = outR;

    /* update coefficient pointer */
    pCoefB = pCoefB + (modifier * 2U);
    pCoefA = pCoefA + ((modifier * 2U) - 1U);

    i--;

  }

  pDst[2U * fftLen] = pSrc[0] - pSrc[1];
  pDst[(2U * fftLen) + 1U] = 0.0f;

  pDst[0] = pSrc[0] + pSrc[1];
  pDst[1] = 0.0f;

}


/**
  @brief         Core Real IFFT process
  @param[in]     pSrc      points to input buffer
  @param[in]     fftLen    length of FFT
  @param[in]     pATable   points to twiddle Coef A buffer
  @param[in]     pBTable   points to twiddle Coef B buffer
  @param[out]    pDst      points to output buffer
  @param[in]     modifier  twiddle coefficient modifier that supports different size FFTs with the same twiddle factor table
  @return        none
 */

void arm_split_rifft_f32(
        float32_t * pSrc,
        uint32_t fftLen,
  const float32_t * pATable,
  const float32_t * pBTable,
        float32_t * pDst,
        uint32_t modifier)
{
        float32_t outR, outI;                          /* Temporary variables for output */
  const float32_t *pCoefA, *pCoefB;                    /* Temporary pointers for twiddle factors */
        float32_t CoefA1, CoefA2, CoefB1;              /* Temporary variables for twiddle coefficients */
        float32_t *pSrc1 = &pSrc[0], *pSrc2 = &pSrc[(2U * fftLen) + 1U];

  pCoefA = &pATable[0];
  pCoefB = &pBTable[0];

  while (fftLen > 0U)
  {
     /*
       outR = (  pIn[2 * i]             * pATable[2 * i]
               + pIn[2 * i + 1]         * pATable[2 * i + 1]
               + pIn[2 * n - 2 * i]     * pBTable[2 * i]
               - pIn[2 * n - 2 * i + 1] * pBTable[2 * i + 1]);

       outI = (  pIn[2 * i + 1]         * pATable[2 * i]
               - pIn[2 * i]             * pATable[2 * i + 1]
               - pIn[2 * n - 2 * i]     * pBTable[2 * i + 1]
               - pIn[2 * n - 2 * i + 1] * pBTable[2 * i]);
      */

     CoefA1 = *pCoefA++;
     CoefA2 = *pCoefA;

     /* outR = (pSrc[2 * i] * CoefA1 */
     outR = *pSrc1 * CoefA1;

     /* - pSrc[2 * i] * CoefA2 */
     outI = -(*pSrc1++) * CoefA2;

     /* (pSrc[2 * i + 1] + pSrc[2 * fftLen - 2 * i + 1]) * CoefA2 */
     outR += (*pSrc1 + *pSrc2) * CoefA2;

     /* pSrc[2 * i + 1] * CoefA1 */
     outI += (*pSrc1++) * CoefA1;

     CoefB1 = *pCoefB;

     /* - pSrc[2 * fftLen - 2 * i + 1] * CoefB1 */
     outI -= *pSrc2-- * CoefB1;

     /* pSrc[2 * fftLen - 2 * i] * CoefB1 */
     outR += *pSrc2 * CoefB1;

     /* pSrc[2 * fftLen - 2 * i] * CoefA2 */
     outI += *pSrc2-- * CoefA2;

     /* write output */
     *pDst++ = outR;
     *pDst++ = outI;

     /* update coefficient pointer */
     pCoefB = pCoefB + (modifier * 2);
     pCoefA = pCoefA + (modifier * 2 - 1);

     /* Decrement loop count */
     fftLen--;
  }

}