/* ----------------------------------------------------------------------
 * Project:      CMSIS DSP Library
 * Title:        arm_cfft_f32.c
 * Description:  Combined Radix Decimation in Frequency CFFT Floating point processing function
 *
 * $Date:        23 April 2021
 * $Revision:    V1.9.0
 *
 * Target Processor: Cortex-M and Cortex-A cores
 * -------------------------------------------------------------------- */
/*
 * Copyright (C) 2010-2021 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 "dsp/transform_functions.h"
#include "arm_common_tables.h"

#if defined(ARM_MATH_MVEF) && !defined(ARM_MATH_AUTOVECTORIZE)

#include "arm_helium_utils.h"
#include "arm_vec_fft.h"
#include "arm_mve_tables.h"


static float32_t arm_inverse_fft_length_f32(uint16_t fftLen)
{
  float32_t retValue=1.0;

  switch (fftLen)
  {

  case 4096U:
    retValue = 0.000244140625;
    break;

  case 2048U:
    retValue = 0.00048828125;
    break;

  case 1024U:
    retValue = 0.0009765625f;
    break;

  case 512U:
    retValue = 0.001953125;
    break;

  case 256U:
    retValue = 0.00390625f;
    break;

  case 128U:
    retValue = 0.0078125;
    break;

  case 64U:
    retValue = 0.015625f;
    break;

  case 32U:
    retValue = 0.03125;
    break;

  case 16U:
    retValue = 0.0625f;
    break;


  default:
    break;
  }
  return(retValue);
}




static void _arm_radix4_butterfly_f32_mve(const arm_cfft_instance_f32 * S,float32_t * pSrc, uint32_t fftLen)
{
    f32x4_t     vecTmp0, vecTmp1;
    f32x4_t     vecSum0, vecDiff0, vecSum1, vecDiff1;
    f32x4_t     vecA, vecB, vecC, vecD;
    uint32_t    blkCnt;
    uint32_t    n1, n2;
    uint32_t    stage = 0;
    int32_t     iter = 1;
    static const int32_t strides[4] = {
        (0 - 16) * (int32_t)sizeof(q31_t *),
        (1 - 16) * (int32_t)sizeof(q31_t *),
        (8 - 16) * (int32_t)sizeof(q31_t *),
        (9 - 16) * (int32_t)sizeof(q31_t *)
    };

    n2 = fftLen;
    n1 = n2;
    n2 >>= 2u;
    for (int k = fftLen / 4u; k > 1; k >>= 2)
    {
        float32_t const     *p_rearranged_twiddle_tab_stride1 =
                            &S->rearranged_twiddle_stride1[
                            S->rearranged_twiddle_tab_stride1_arr[stage]];
        float32_t const     *p_rearranged_twiddle_tab_stride2 =
                            &S->rearranged_twiddle_stride2[
                            S->rearranged_twiddle_tab_stride2_arr[stage]];
        float32_t const     *p_rearranged_twiddle_tab_stride3 =
                            &S->rearranged_twiddle_stride3[
                            S->rearranged_twiddle_tab_stride3_arr[stage]];

        float32_t * pBase = pSrc;
        for (int i = 0; i < iter; i++)
        {
            float32_t    *inA = pBase;
            float32_t    *inB = inA + n2 * CMPLX_DIM;
            float32_t    *inC = inB + n2 * CMPLX_DIM;
            float32_t    *inD = inC + n2 * CMPLX_DIM;
            float32_t const *pW1 = p_rearranged_twiddle_tab_stride1;
            float32_t const *pW2 = p_rearranged_twiddle_tab_stride2;
            float32_t const *pW3 = p_rearranged_twiddle_tab_stride3;
            f32x4_t            vecW;

            blkCnt = n2 / 2;
            /*
             * load 2 f32 complex pair
             */
            vecA = vldrwq_f32(inA);
            vecC = vldrwq_f32(inC);
            while (blkCnt > 0U)
            {
                vecB = vldrwq_f32(inB);
                vecD = vldrwq_f32(inD);

                vecSum0 = vecA + vecC;  /* vecSum0 = vaddq(vecA, vecC) */
                vecDiff0 = vecA - vecC; /* vecSum0 = vsubq(vecA, vecC) */

                vecSum1 = vecB + vecD;
                vecDiff1 = vecB - vecD;
                /*
                 * [ 1 1 1 1 ] * [ A B C D ]' .* 1
                 */
                vecTmp0 = vecSum0 + vecSum1;
                vst1q(inA, vecTmp0);
                inA += 4;

                /*
                 * [ 1 -1 1 -1 ] * [ A B C D ]'
                 */
                vecTmp0 = vecSum0 - vecSum1;
                /*
                 * [ 1 -1 1 -1 ] * [ A B C D ]'.* W2
                 */
                vecW = vld1q(pW2);
                pW2 += 4;
                vecTmp1 = MVE_CMPLX_MULT_FLT_Conj_AxB(vecW, vecTmp0);
                vst1q(inB, vecTmp1);
                inB += 4;

                /*
                 * [ 1 -i -1 +i ] * [ A B C D ]'
                 */
                vecTmp0 = MVE_CMPLX_SUB_A_ixB(vecDiff0, vecDiff1);
                /*
                 * [ 1 -i -1 +i ] * [ A B C D ]'.* W1
                 */
                vecW = vld1q(pW1);
                pW1 +=4;
                vecTmp1 = MVE_CMPLX_MULT_FLT_Conj_AxB(vecW, vecTmp0);
                vst1q(inC, vecTmp1);
                inC += 4;

                /*
                 * [ 1 +i -1 -i ] * [ A B C D ]'
                 */
                vecTmp0 = MVE_CMPLX_ADD_A_ixB(vecDiff0, vecDiff1);
                /*
                 * [ 1 +i -1 -i ] * [ A B C D ]'.* W3
                 */
                vecW = vld1q(pW3);
                pW3 += 4;
                vecTmp1 = MVE_CMPLX_MULT_FLT_Conj_AxB(vecW, vecTmp0);
                vst1q(inD, vecTmp1);
                inD += 4;

                vecA = vldrwq_f32(inA);
                vecC = vldrwq_f32(inC);

                blkCnt--;
            }
            pBase +=  CMPLX_DIM * n1;
        }
        n1 = n2;
        n2 >>= 2u;
        iter = iter << 2;
        stage++;
    }

    /*
     * start of Last stage process
     */
    uint32x4_t vecScGathAddr = vld1q_u32((uint32_t*)strides);
    vecScGathAddr = vecScGathAddr + (uint32_t) pSrc;

    /* load scheduling */
    vecA = vldrwq_gather_base_wb_f32(&vecScGathAddr, 64);
    vecC = vldrwq_gather_base_f32(vecScGathAddr, 16);

    blkCnt = (fftLen >> 3);
    while (blkCnt > 0U)
    {
        vecSum0 = vecA + vecC;  /* vecSum0 = vaddq(vecA, vecC) */
        vecDiff0 = vecA - vecC; /* vecSum0 = vsubq(vecA, vecC) */

        vecB = vldrwq_gather_base_f32(vecScGathAddr, 8);
        vecD = vldrwq_gather_base_f32(vecScGathAddr, 24);

        vecSum1 = vecB + vecD;
        vecDiff1 = vecB - vecD;

        /* pre-load for next iteration */
        vecA = vldrwq_gather_base_wb_f32(&vecScGathAddr, 64);
        vecC = vldrwq_gather_base_f32(vecScGathAddr, 16);

        vecTmp0 = vecSum0 + vecSum1;
        vstrwq_scatter_base_f32(vecScGathAddr, -64, vecTmp0);

        vecTmp0 = vecSum0 - vecSum1;
        vstrwq_scatter_base_f32(vecScGathAddr, -64 + 8, vecTmp0);

        vecTmp0 = MVE_CMPLX_SUB_A_ixB(vecDiff0, vecDiff1);
        vstrwq_scatter_base_f32(vecScGathAddr, -64 + 16, vecTmp0);

        vecTmp0 = MVE_CMPLX_ADD_A_ixB(vecDiff0, vecDiff1);
        vstrwq_scatter_base_f32(vecScGathAddr, -64 + 24, vecTmp0);

        blkCnt--;
    }

    /*
     * End of last stage process
     */
}

static void arm_cfft_radix4by2_f32_mve(const arm_cfft_instance_f32 * S, float32_t *pSrc, uint32_t fftLen)
{
    float32_t const *pCoefVec;
    float32_t const  *pCoef = S->pTwiddle;
    float32_t        *pIn0, *pIn1;
    uint32_t          n2;
    uint32_t          blkCnt;
    f32x4_t         vecIn0, vecIn1, vecSum, vecDiff;
    f32x4_t         vecCmplxTmp, vecTw;


    n2 = fftLen >> 1;
    pIn0 = pSrc;
    pIn1 = pSrc + fftLen;
    pCoefVec = pCoef;

    blkCnt = n2 / 2;
    while (blkCnt > 0U)
    {
        vecIn0 = *(f32x4_t *) pIn0;
        vecIn1 = *(f32x4_t *) pIn1;
        vecTw = vld1q(pCoefVec);
        pCoefVec += 4;

        vecSum = vecIn0 + vecIn1;
        vecDiff = vecIn0 - vecIn1;

        vecCmplxTmp = MVE_CMPLX_MULT_FLT_Conj_AxB(vecTw, vecDiff);

        vst1q(pIn0, vecSum);
        pIn0 += 4;
        vst1q(pIn1, vecCmplxTmp);
        pIn1 += 4;

        blkCnt--;
    }

    _arm_radix4_butterfly_f32_mve(S, pSrc, n2);

    _arm_radix4_butterfly_f32_mve(S, pSrc + fftLen, n2);

    pIn0 = pSrc;
}

static void _arm_radix4_butterfly_inverse_f32_mve(const arm_cfft_instance_f32 * S,float32_t * pSrc, uint32_t fftLen, float32_t onebyfftLen)
{
    f32x4_t vecTmp0, vecTmp1;
    f32x4_t vecSum0, vecDiff0, vecSum1, vecDiff1;
    f32x4_t vecA, vecB, vecC, vecD;
    uint32_t  blkCnt;
    uint32_t  n1, n2;
    uint32_t  stage = 0;
    int32_t  iter = 1;
    static const int32_t strides[4] = {
        (0 - 16) * (int32_t)sizeof(q31_t *),
        (1 - 16) * (int32_t)sizeof(q31_t *),
        (8 - 16) * (int32_t)sizeof(q31_t *),
        (9 - 16) * (int32_t)sizeof(q31_t *)
    };

    n2 = fftLen;
    n1 = n2;
    n2 >>= 2u;
    for (int k = fftLen / 4; k > 1; k >>= 2)
    {
        float32_t const *p_rearranged_twiddle_tab_stride1 =
                &S->rearranged_twiddle_stride1[
                S->rearranged_twiddle_tab_stride1_arr[stage]];
        float32_t const *p_rearranged_twiddle_tab_stride2 =
                &S->rearranged_twiddle_stride2[
                S->rearranged_twiddle_tab_stride2_arr[stage]];
        float32_t const *p_rearranged_twiddle_tab_stride3 =
                &S->rearranged_twiddle_stride3[
                S->rearranged_twiddle_tab_stride3_arr[stage]];

        float32_t * pBase = pSrc;
        for (int i = 0; i < iter; i++)
        {
            float32_t    *inA = pBase;
            float32_t    *inB = inA + n2 * CMPLX_DIM;
            float32_t    *inC = inB + n2 * CMPLX_DIM;
            float32_t    *inD = inC + n2 * CMPLX_DIM;
            float32_t const *pW1 = p_rearranged_twiddle_tab_stride1;
            float32_t const *pW2 = p_rearranged_twiddle_tab_stride2;
            float32_t const *pW3 = p_rearranged_twiddle_tab_stride3;
            f32x4_t       vecW;

            blkCnt = n2 / 2;
            /*
             * load 2 f32 complex pair
             */
            vecA = vldrwq_f32(inA);
            vecC = vldrwq_f32(inC);
            while (blkCnt > 0U)
            {
                vecB = vldrwq_f32(inB);
                vecD = vldrwq_f32(inD);

                vecSum0 = vecA + vecC;  /* vecSum0 = vaddq(vecA, vecC) */
                vecDiff0 = vecA - vecC; /* vecSum0 = vsubq(vecA, vecC) */

                vecSum1 = vecB + vecD;
                vecDiff1 = vecB - vecD;
                /*
                 * [ 1 1 1 1 ] * [ A B C D ]' .* 1
                 */
                vecTmp0 = vecSum0 + vecSum1;
                vst1q(inA, vecTmp0);
                inA += 4;
                /*
                 * [ 1 -1 1 -1 ] * [ A B C D ]'
                 */
                vecTmp0 = vecSum0 - vecSum1;
                /*
                 * [ 1 -1 1 -1 ] * [ A B C D ]'.* W1
                 */
                vecW = vld1q(pW2);
                pW2 += 4;
                vecTmp1 = MVE_CMPLX_MULT_FLT_AxB(vecW, vecTmp0);
                vst1q(inB, vecTmp1);
                inB += 4;

                /*
                 * [ 1 -i -1 +i ] * [ A B C D ]'
                 */
                vecTmp0 = MVE_CMPLX_ADD_A_ixB(vecDiff0, vecDiff1);
                /*
                 * [ 1 -i -1 +i ] * [ A B C D ]'.* W2
                 */
                vecW = vld1q(pW1);
                pW1 += 4;
                vecTmp1 = MVE_CMPLX_MULT_FLT_AxB(vecW, vecTmp0);
                vst1q(inC, vecTmp1);
                inC += 4;

                /*
                 * [ 1 +i -1 -i ] * [ A B C D ]'
                 */
                vecTmp0 = MVE_CMPLX_SUB_A_ixB(vecDiff0, vecDiff1);
                /*
                 * [ 1 +i -1 -i ] * [ A B C D ]'.* W3
                 */
                vecW = vld1q(pW3);
                pW3 += 4;
                vecTmp1 = MVE_CMPLX_MULT_FLT_AxB(vecW, vecTmp0);
                vst1q(inD, vecTmp1);
                inD += 4;

                vecA = vldrwq_f32(inA);
                vecC = vldrwq_f32(inC);

                blkCnt--;
            }
            pBase +=  CMPLX_DIM * n1;
        }
        n1 = n2;
        n2 >>= 2u;
        iter = iter << 2;
        stage++;
    }

    /*
     * start of Last stage process
     */
    uint32x4_t vecScGathAddr = vld1q_u32 ((uint32_t*)strides);
    vecScGathAddr = vecScGathAddr + (uint32_t) pSrc;

    /*
     * load scheduling
     */
    vecA = vldrwq_gather_base_wb_f32(&vecScGathAddr, 64);
    vecC = vldrwq_gather_base_f32(vecScGathAddr, 16);

    blkCnt = (fftLen >> 3);
    while (blkCnt > 0U)
    {
        vecSum0 = vecA + vecC;  /* vecSum0 = vaddq(vecA, vecC) */
        vecDiff0 = vecA - vecC; /* vecSum0 = vsubq(vecA, vecC) */

        vecB = vldrwq_gather_base_f32(vecScGathAddr, 8);
        vecD = vldrwq_gather_base_f32(vecScGathAddr, 24);

        vecSum1 = vecB + vecD;
        vecDiff1 = vecB - vecD;

        vecA = vldrwq_gather_base_wb_f32(&vecScGathAddr, 64);
        vecC = vldrwq_gather_base_f32(vecScGathAddr, 16);

        vecTmp0 = vecSum0 + vecSum1;
        vecTmp0 = vecTmp0 * onebyfftLen;
        vstrwq_scatter_base_f32(vecScGathAddr, -64, vecTmp0);

        vecTmp0 = vecSum0 - vecSum1;
        vecTmp0 = vecTmp0 * onebyfftLen;
        vstrwq_scatter_base_f32(vecScGathAddr, -64 + 8, vecTmp0);

        vecTmp0 = MVE_CMPLX_ADD_A_ixB(vecDiff0, vecDiff1);
        vecTmp0 = vecTmp0 * onebyfftLen;
        vstrwq_scatter_base_f32(vecScGathAddr, -64 + 16, vecTmp0);

        vecTmp0 = MVE_CMPLX_SUB_A_ixB(vecDiff0, vecDiff1);
        vecTmp0 = vecTmp0 * onebyfftLen;
        vstrwq_scatter_base_f32(vecScGathAddr, -64 + 24, vecTmp0);

        blkCnt--;
    }

    /*
     * End of last stage process
     */
}

static void arm_cfft_radix4by2_inverse_f32_mve(const arm_cfft_instance_f32 * S,float32_t *pSrc, uint32_t fftLen)
{
    float32_t const *pCoefVec;
    float32_t const  *pCoef = S->pTwiddle;
    float32_t        *pIn0, *pIn1;
    uint32_t          n2;
    float32_t         onebyfftLen = arm_inverse_fft_length_f32(fftLen);
    uint32_t          blkCnt;
    f32x4_t         vecIn0, vecIn1, vecSum, vecDiff;
    f32x4_t         vecCmplxTmp, vecTw;


    n2 = fftLen >> 1;
    pIn0 = pSrc;
    pIn1 = pSrc + fftLen;
    pCoefVec = pCoef;

    blkCnt = n2 / 2;
    while (blkCnt > 0U)
    {
        vecIn0 = *(f32x4_t *) pIn0;
        vecIn1 = *(f32x4_t *) pIn1;
        vecTw = vld1q(pCoefVec);
        pCoefVec += 4;

        vecSum = vecIn0 + vecIn1;
        vecDiff = vecIn0 - vecIn1;

        vecCmplxTmp = MVE_CMPLX_MULT_FLT_AxB(vecTw, vecDiff);

        vst1q(pIn0, vecSum);
        pIn0 += 4;
        vst1q(pIn1, vecCmplxTmp);
        pIn1 += 4;

        blkCnt--;
    }

    _arm_radix4_butterfly_inverse_f32_mve(S, pSrc, n2, onebyfftLen);

    _arm_radix4_butterfly_inverse_f32_mve(S, pSrc + fftLen, n2, onebyfftLen);
}


/**
  @addtogroup ComplexFFT
  @{
 */

/**
  @brief         Processing function for the floating-point complex FFT.
  @param[in]     S              points to an instance of the floating-point CFFT structure
  @param[in,out] p1             points to the complex data buffer of size <code>2*fftLen</code>. Processing occurs in-place
  @param[in]     ifftFlag       flag that selects transform direction
                   - value = 0: forward transform
                   - value = 1: inverse transform
  @param[in]     bitReverseFlag flag that enables / disables bit reversal of output
                   - value = 0: disables bit reversal of output
                   - value = 1: enables bit reversal of output
  @return        none
 */


void arm_cfft_f32(
  const arm_cfft_instance_f32 * S,
        float32_t * pSrc,
        uint8_t ifftFlag,
        uint8_t bitReverseFlag)
{
        uint32_t fftLen = S->fftLen;

        if (ifftFlag == 1U) {

            switch (fftLen) {
            case 16:
            case 64:
            case 256:
            case 1024:
            case 4096:
                _arm_radix4_butterfly_inverse_f32_mve(S, pSrc, fftLen, arm_inverse_fft_length_f32(S->fftLen));
                break;

            case 32:
            case 128:
            case 512:
            case 2048:
                arm_cfft_radix4by2_inverse_f32_mve(S, pSrc, fftLen);
                break;
            }
        } else {
            switch (fftLen) {
            case 16:
            case 64:
            case 256:
            case 1024:
            case 4096:
                _arm_radix4_butterfly_f32_mve(S, pSrc, fftLen);
                break;

            case 32:
            case 128:
            case 512:
            case 2048:
                arm_cfft_radix4by2_f32_mve(S, pSrc, fftLen);
                break;
            }
        }


        if (bitReverseFlag)
        {

            arm_bitreversal_32_inpl_mve((uint32_t*)pSrc, S->bitRevLength, S->pBitRevTable);

        }
}


#else
extern void arm_radix8_butterfly_f32(
        float32_t * pSrc,
        uint16_t fftLen,
  const float32_t * pCoef,
        uint16_t twidCoefModifier);

extern void arm_bitreversal_32(
        uint32_t * pSrc,
  const uint16_t bitRevLen,
  const uint16_t * pBitRevTable);

/**
  @ingroup groupTransforms
 */

/**
  @defgroup ComplexFFT Complex FFT Functions

  @par
                   The Fast Fourier Transform (FFT) is an efficient algorithm for computing the
                   Discrete Fourier Transform (DFT).  The FFT can be orders of magnitude faster
                   than the DFT, especially for long lengths.
                   The algorithms described in this section
                   operate on complex data.  A separate set of functions is devoted to handling
                   of real sequences.
  @par
                   There are separate algorithms for handling floating-point, Q15, and Q31 data
                   types.  The algorithms available for each data type are described next.
  @par
                   The FFT functions operate in-place.  That is, the array holding the input data
                   will also be used to hold the corresponding result.  The input data is complex
                   and contains <code>2*fftLen</code> interleaved values as shown below.
                   <pre>{real[0], imag[0], real[1], imag[1], ...} </pre>
                   The FFT result will be contained in the same array and the frequency domain
                   values will have the same interleaving.

  @par Floating-point
                   The floating-point complex FFT uses a mixed-radix algorithm.  Multiple radix-8
                   stages are performed along with a single radix-2 or radix-4 stage, as needed.
                   The algorithm supports lengths of [16, 32, 64, ..., 4096] and each length uses
                   a different twiddle factor table.
  @par
                   The function uses the standard FFT definition and output values may grow by a
                   factor of <code>fftLen</code> when computing the forward transform.  The
                   inverse transform includes a scale of <code>1/fftLen</code> as part of the
                   calculation and this matches the textbook definition of the inverse FFT.
  @par
                   For the MVE version, the new arm_cfft_init_f32 initialization function is
                   <b>mandatory</b>. <b>Compilation flags are available to include only the required tables for the
                   needed FFTs.</b> Other FFT versions can continue to be initialized as
                   explained below.
  @par
                   For not MVE versions, pre-initialized data structures containing twiddle factors
                   and bit reversal tables are provided and defined in <code>arm_const_structs.h</code>.  Include
                   this header in your function and then pass one of the constant structures as
                   an argument to arm_cfft_f32.  For example:
  @par
                   <code>arm_cfft_f32(arm_cfft_sR_f32_len64, pSrc, 1, 1)</code>
  @par
                   computes a 64-point inverse complex FFT including bit reversal.
                   The data structures are treated as constant data and not modified during the
                   calculation.  The same data structure can be reused for multiple transforms
                   including mixing forward and inverse transforms.
  @par
                   Earlier releases of the library provided separate radix-2 and radix-4
                   algorithms that operated on floating-point data.  These functions are still
                   provided but are deprecated.  The older functions are slower and less general
                   than the new functions.
  @par
                   An example of initialization of the constants for the arm_cfft_f32 function follows:
  @code
                   const static arm_cfft_instance_f32 *S;
                   ...
                     switch (length) {
                       case 16:
                         S = &arm_cfft_sR_f32_len16;
                         break;
                       case 32:
                         S = &arm_cfft_sR_f32_len32;
                         break;
                       case 64:
                         S = &arm_cfft_sR_f32_len64;
                         break;
                       case 128:
                         S = &arm_cfft_sR_f32_len128;
                         break;
                       case 256:
                         S = &arm_cfft_sR_f32_len256;
                         break;
                       case 512:
                         S = &arm_cfft_sR_f32_len512;
                         break;
                       case 1024:
                         S = &arm_cfft_sR_f32_len1024;
                         break;
                       case 2048:
                         S = &arm_cfft_sR_f32_len2048;
                         break;
                       case 4096:
                         S = &arm_cfft_sR_f32_len4096;
                         break;
                     }
  @endcode
  @par
                   The new arm_cfft_init_f32 can also be used.
  @par Q15 and Q31
                   The floating-point complex FFT uses a mixed-radix algorithm.  Multiple radix-4
                   stages are performed along with a single radix-2 stage, as needed.
                   The algorithm supports lengths of [16, 32, 64, ..., 4096] and each length uses
                   a different twiddle factor table.
  @par
                   The function uses the standard FFT definition and output values may grow by a
                   factor of <code>fftLen</code> when computing the forward transform.  The
                   inverse transform includes a scale of <code>1/fftLen</code> as part of the
                   calculation and this matches the textbook definition of the inverse FFT.
  @par
                   Pre-initialized data structures containing twiddle factors and bit reversal
                   tables are provided and defined in <code>arm_const_structs.h</code>.  Include
                   this header in your function and then pass one of the constant structures as
                   an argument to arm_cfft_q31. For example:
  @par
                   <code>arm_cfft_q31(arm_cfft_sR_q31_len64, pSrc, 1, 1)</code>
  @par
                   computes a 64-point inverse complex FFT including bit reversal.
                   The data structures are treated as constant data and not modified during the
                   calculation.  The same data structure can be reused for multiple transforms
                   including mixing forward and inverse transforms.
  @par
                   Earlier releases of the library provided separate radix-2 and radix-4
                   algorithms that operated on floating-point data.  These functions are still
                   provided but are deprecated.  The older functions are slower and less general
                   than the new functions.
  @par
                   An example of initialization of the constants for the arm_cfft_q31 function follows:
  @code
                   const static arm_cfft_instance_q31 *S;
                   ...
                     switch (length) {
                       case 16:
                         S = &arm_cfft_sR_q31_len16;
                         break;
                       case 32:
                         S = &arm_cfft_sR_q31_len32;
                         break;
                       case 64:
                         S = &arm_cfft_sR_q31_len64;
                         break;
                       case 128:
                         S = &arm_cfft_sR_q31_len128;
                         break;
                       case 256:
                         S = &arm_cfft_sR_q31_len256;
                         break;
                       case 512:
                         S = &arm_cfft_sR_q31_len512;
                         break;
                       case 1024:
                         S = &arm_cfft_sR_q31_len1024;
                         break;
                       case 2048:
                         S = &arm_cfft_sR_q31_len2048;
                         break;
                       case 4096:
                         S = &arm_cfft_sR_q31_len4096;
                         break;
                     }
  @endcode

 */

void arm_cfft_radix8by2_f32 (arm_cfft_instance_f32 * S, float32_t * p1)
{
  uint32_t    L  = S->fftLen;
  float32_t * pCol1, * pCol2, * pMid1, * pMid2;
  float32_t * p2 = p1 + L;
  const float32_t * tw = (float32_t *) S->pTwiddle;
  float32_t t1[4], t2[4], t3[4], t4[4], twR, twI;
  float32_t m0, m1, m2, m3;
  uint32_t l;

  pCol1 = p1;
  pCol2 = p2;

  /* Define new length */
  L >>= 1;

  /* Initialize mid pointers */
  pMid1 = p1 + L;
  pMid2 = p2 + L;

  /* do two dot Fourier transform */
  for (l = L >> 2; l > 0; l-- )
  {
    t1[0] = p1[0];
    t1[1] = p1[1];
    t1[2] = p1[2];
    t1[3] = p1[3];

    t2[0] = p2[0];
    t2[1] = p2[1];
    t2[2] = p2[2];
    t2[3] = p2[3];

    t3[0] = pMid1[0];
    t3[1] = pMid1[1];
    t3[2] = pMid1[2];
    t3[3] = pMid1[3];

    t4[0] = pMid2[0];
    t4[1] = pMid2[1];
    t4[2] = pMid2[2];
    t4[3] = pMid2[3];

    *p1++ = t1[0] + t2[0];
    *p1++ = t1[1] + t2[1];
    *p1++ = t1[2] + t2[2];
    *p1++ = t1[3] + t2[3];    /* col 1 */

    t2[0] = t1[0] - t2[0];
    t2[1] = t1[1] - t2[1];
    t2[2] = t1[2] - t2[2];
    t2[3] = t1[3] - t2[3];    /* for col 2 */

    *pMid1++ = t3[0] + t4[0];
    *pMid1++ = t3[1] + t4[1];
    *pMid1++ = t3[2] + t4[2];
    *pMid1++ = t3[3] + t4[3]; /* col 1 */

    t4[0] = t4[0] - t3[0];
    t4[1] = t4[1] - t3[1];
    t4[2] = t4[2] - t3[2];
    t4[3] = t4[3] - t3[3];    /* for col 2 */

    twR = *tw++;
    twI = *tw++;

    /* multiply by twiddle factors */
    m0 = t2[0] * twR;
    m1 = t2[1] * twI;
    m2 = t2[1] * twR;
    m3 = t2[0] * twI;

    /* R  =  R  *  Tr - I * Ti */
    *p2++ = m0 + m1;
    /* I  =  I  *  Tr + R * Ti */
    *p2++ = m2 - m3;

    /* use vertical symmetry */
    /*  0.9988 - 0.0491i <==> -0.0491 - 0.9988i */
    m0 = t4[0] * twI;
    m1 = t4[1] * twR;
    m2 = t4[1] * twI;
    m3 = t4[0] * twR;

    *pMid2++ = m0 - m1;
    *pMid2++ = m2 + m3;

    twR = *tw++;
    twI = *tw++;

    m0 = t2[2] * twR;
    m1 = t2[3] * twI;
    m2 = t2[3] * twR;
    m3 = t2[2] * twI;

    *p2++ = m0 + m1;
    *p2++ = m2 - m3;

    m0 = t4[2] * twI;
    m1 = t4[3] * twR;
    m2 = t4[3] * twI;
    m3 = t4[2] * twR;

    *pMid2++ = m0 - m1;
    *pMid2++ = m2 + m3;
  }

  /* first col */
  arm_radix8_butterfly_f32 (pCol1, L, (float32_t *) S->pTwiddle, 2U);

  /* second col */
  arm_radix8_butterfly_f32 (pCol2, L, (float32_t *) S->pTwiddle, 2U);
}

void arm_cfft_radix8by4_f32 (arm_cfft_instance_f32 * S, float32_t * p1)
{
    uint32_t    L  = S->fftLen >> 1;
    float32_t * pCol1, *pCol2, *pCol3, *pCol4, *pEnd1, *pEnd2, *pEnd3, *pEnd4;
    const float32_t *tw2, *tw3, *tw4;
    float32_t * p2 = p1 + L;
    float32_t * p3 = p2 + L;
    float32_t * p4 = p3 + L;
    float32_t t2[4], t3[4], t4[4], twR, twI;
    float32_t p1ap3_0, p1sp3_0, p1ap3_1, p1sp3_1;
    float32_t m0, m1, m2, m3;
    uint32_t l, twMod2, twMod3, twMod4;

    pCol1 = p1;         /* points to real values by default */
    pCol2 = p2;
    pCol3 = p3;
    pCol4 = p4;
    pEnd1 = p2 - 1;     /* points to imaginary values by default */
    pEnd2 = p3 - 1;
    pEnd3 = p4 - 1;
    pEnd4 = pEnd3 + L;

    tw2 = tw3 = tw4 = (float32_t *) S->pTwiddle;

    L >>= 1;

    /* do four dot Fourier transform */

    twMod2 = 2;
    twMod3 = 4;
    twMod4 = 6;

    /* TOP */
    p1ap3_0 = p1[0] + p3[0];
    p1sp3_0 = p1[0] - p3[0];
    p1ap3_1 = p1[1] + p3[1];
    p1sp3_1 = p1[1] - p3[1];

    /* col 2 */
    t2[0] = p1sp3_0 + p2[1] - p4[1];
    t2[1] = p1sp3_1 - p2[0] + p4[0];
    /* col 3 */
    t3[0] = p1ap3_0 - p2[0] - p4[0];
    t3[1] = p1ap3_1 - p2[1] - p4[1];
    /* col 4 */
    t4[0] = p1sp3_0 - p2[1] + p4[1];
    t4[1] = p1sp3_1 + p2[0] - p4[0];
    /* col 1 */
    *p1++ = p1ap3_0 + p2[0] + p4[0];
    *p1++ = p1ap3_1 + p2[1] + p4[1];

    /* Twiddle factors are ones */
    *p2++ = t2[0];
    *p2++ = t2[1];
    *p3++ = t3[0];
    *p3++ = t3[1];
    *p4++ = t4[0];
    *p4++ = t4[1];

    tw2 += twMod2;
    tw3 += twMod3;
    tw4 += twMod4;

    for (l = (L - 2) >> 1; l > 0; l-- )
    {
      /* TOP */
      p1ap3_0 = p1[0] + p3[0];
      p1sp3_0 = p1[0] - p3[0];
      p1ap3_1 = p1[1] + p3[1];
      p1sp3_1 = p1[1] - p3[1];
      /* col 2 */
      t2[0] = p1sp3_0 + p2[1] - p4[1];
      t2[1] = p1sp3_1 - p2[0] + p4[0];
      /* col 3 */
      t3[0] = p1ap3_0 - p2[0] - p4[0];
      t3[1] = p1ap3_1 - p2[1] - p4[1];
      /* col 4 */
      t4[0] = p1sp3_0 - p2[1] + p4[1];
      t4[1] = p1sp3_1 + p2[0] - p4[0];
      /* col 1 - top */
      *p1++ = p1ap3_0 + p2[0] + p4[0];
      *p1++ = p1ap3_1 + p2[1] + p4[1];

      /* BOTTOM */
      p1ap3_1 = pEnd1[-1] + pEnd3[-1];
      p1sp3_1 = pEnd1[-1] - pEnd3[-1];
      p1ap3_0 = pEnd1[ 0] + pEnd3[0];
      p1sp3_0 = pEnd1[ 0] - pEnd3[0];
      /* col 2 */
      t2[2] = pEnd2[0] - pEnd4[0] + p1sp3_1;
      t2[3] = pEnd1[0] - pEnd3[0] - pEnd2[-1] + pEnd4[-1];
      /* col 3 */
      t3[2] = p1ap3_1 - pEnd2[-1] - pEnd4[-1];
      t3[3] = p1ap3_0 - pEnd2[ 0] - pEnd4[ 0];
      /* col 4 */
      t4[2] = pEnd2[ 0] - pEnd4[ 0] - p1sp3_1;
      t4[3] = pEnd4[-1] - pEnd2[-1] - p1sp3_0;
      /* col 1 - Bottom */
      *pEnd1-- = p1ap3_0 + pEnd2[ 0] + pEnd4[ 0];
      *pEnd1-- = p1ap3_1 + pEnd2[-1] + pEnd4[-1];

      /* COL 2 */
      /* read twiddle factors */
      twR = *tw2++;
      twI = *tw2++;
      /* multiply by twiddle factors */
      /*  let    Z1 = a + i(b),   Z2 = c + i(d) */
      /*   =>  Z1 * Z2  =  (a*c - b*d) + i(b*c + a*d) */

      /* Top */
      m0 = t2[0] * twR;
      m1 = t2[1] * twI;
      m2 = t2[1] * twR;
      m3 = t2[0] * twI;

      *p2++ = m0 + m1;
      *p2++ = m2 - m3;
      /* use vertical symmetry col 2 */
      /* 0.9997 - 0.0245i  <==>  0.0245 - 0.9997i */
      /* Bottom */
      m0 = t2[3] * twI;
      m1 = t2[2] * twR;
      m2 = t2[2] * twI;
      m3 = t2[3] * twR;

      *pEnd2-- = m0 - m1;
      *pEnd2-- = m2 + m3;

      /* COL 3 */
      twR = tw3[0];
      twI = tw3[1];
      tw3 += twMod3;
      /* Top */
      m0 = t3[0] * twR;
      m1 = t3[1] * twI;
      m2 = t3[1] * twR;
      m3 = t3[0] * twI;

      *p3++ = m0 + m1;
      *p3++ = m2 - m3;
      /* use vertical symmetry col 3 */
      /* 0.9988 - 0.0491i  <==>  -0.9988 - 0.0491i */
      /* Bottom */
      m0 = -t3[3] * twR;
      m1 =  t3[2] * twI;
      m2 =  t3[2] * twR;
      m3 =  t3[3] * twI;

      *pEnd3-- = m0 - m1;
      *pEnd3-- = m3 - m2;

      /* COL 4 */
      twR = tw4[0];
      twI = tw4[1];
      tw4 += twMod4;
      /* Top */
      m0 = t4[0] * twR;
      m1 = t4[1] * twI;
      m2 = t4[1] * twR;
      m3 = t4[0] * twI;

      *p4++ = m0 + m1;
      *p4++ = m2 - m3;
      /* use vertical symmetry col 4 */
      /* 0.9973 - 0.0736i  <==>  -0.0736 + 0.9973i */
      /* Bottom */
      m0 = t4[3] * twI;
      m1 = t4[2] * twR;
      m2 = t4[2] * twI;
      m3 = t4[3] * twR;

      *pEnd4-- = m0 - m1;
      *pEnd4-- = m2 + m3;
    }

    /* MIDDLE */
    /* Twiddle factors are */
    /*  1.0000  0.7071-0.7071i  -1.0000i  -0.7071-0.7071i */
    p1ap3_0 = p1[0] + p3[0];
    p1sp3_0 = p1[0] - p3[0];
    p1ap3_1 = p1[1] + p3[1];
    p1sp3_1 = p1[1] - p3[1];

    /* col 2 */
    t2[0] = p1sp3_0 + p2[1] - p4[1];
    t2[1] = p1sp3_1 - p2[0] + p4[0];
    /* col 3 */
    t3[0] = p1ap3_0 - p2[0] - p4[0];
    t3[1] = p1ap3_1 - p2[1] - p4[1];
    /* col 4 */
    t4[0] = p1sp3_0 - p2[1] + p4[1];
    t4[1] = p1sp3_1 + p2[0] - p4[0];
    /* col 1 - Top */
    *p1++ = p1ap3_0 + p2[0] + p4[0];
    *p1++ = p1ap3_1 + p2[1] + p4[1];

    /* COL 2 */
    twR = tw2[0];
    twI = tw2[1];

    m0 = t2[0] * twR;
    m1 = t2[1] * twI;
    m2 = t2[1] * twR;
    m3 = t2[0] * twI;

    *p2++ = m0 + m1;
    *p2++ = m2 - m3;
    /* COL 3 */
    twR = tw3[0];
    twI = tw3[1];

    m0 = t3[0] * twR;
    m1 = t3[1] * twI;
    m2 = t3[1] * twR;
    m3 = t3[0] * twI;

    *p3++ = m0 + m1;
    *p3++ = m2 - m3;
    /* COL 4 */
    twR = tw4[0];
    twI = tw4[1];

    m0 = t4[0] * twR;
    m1 = t4[1] * twI;
    m2 = t4[1] * twR;
    m3 = t4[0] * twI;

    *p4++ = m0 + m1;
    *p4++ = m2 - m3;

    /* first col */
    arm_radix8_butterfly_f32 (pCol1, L, (float32_t *) S->pTwiddle, 4U);

    /* second col */
    arm_radix8_butterfly_f32 (pCol2, L, (float32_t *) S->pTwiddle, 4U);

    /* third col */
    arm_radix8_butterfly_f32 (pCol3, L, (float32_t *) S->pTwiddle, 4U);

    /* fourth col */
    arm_radix8_butterfly_f32 (pCol4, L, (float32_t *) S->pTwiddle, 4U);
}

/**
  @addtogroup ComplexFFT
  @{
 */

/**
  @brief         Processing function for the floating-point complex FFT.
  @param[in]     S              points to an instance of the floating-point CFFT structure
  @param[in,out] p1             points to the complex data buffer of size <code>2*fftLen</code>. Processing occurs in-place
  @param[in]     ifftFlag       flag that selects transform direction
                   - value = 0: forward transform
                   - value = 1: inverse transform
  @param[in]     bitReverseFlag flag that enables / disables bit reversal of output
                   - value = 0: disables bit reversal of output
                   - value = 1: enables bit reversal of output
  @return        none
 */

void arm_cfft_f32(
  const arm_cfft_instance_f32 * S,
        float32_t * p1,
        uint8_t ifftFlag,
        uint8_t bitReverseFlag)
{
  uint32_t  L = S->fftLen, l;
  float32_t invL, * pSrc;

  if (ifftFlag == 1U)
  {
    /* Conjugate input data */
    pSrc = p1 + 1;
    for (l = 0; l < L; l++)
    {
      *pSrc = -*pSrc;
      pSrc += 2;
    }
  }

  switch (L)
  {
  case 16:
  case 128:
  case 1024:
    arm_cfft_radix8by2_f32 ( (arm_cfft_instance_f32 *) S, p1);
    break;
  case 32:
  case 256:
  case 2048:
    arm_cfft_radix8by4_f32 ( (arm_cfft_instance_f32 *) S, p1);
    break;
  case 64:
  case 512:
  case 4096:
    arm_radix8_butterfly_f32 ( p1, L, (float32_t *) S->pTwiddle, 1);
    break;
  }

  if ( bitReverseFlag )
    arm_bitreversal_32 ((uint32_t*) p1, S->bitRevLength, S->pBitRevTable);

  if (ifftFlag == 1U)
  {
    invL = 1.0f / (float32_t)L;

    /* Conjugate and scale output data */
    pSrc = p1;
    for (l= 0; l < L; l++)
    {
      *pSrc++ *=   invL ;
      *pSrc    = -(*pSrc) * invL;
      pSrc++;
    }
  }
}
#endif /* defined(ARM_MATH_MVEF) && !defined(ARM_MATH_AUTOVECTORIZE) */

/**
  @} end of ComplexFFT group
 */
