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/* ----------------------------------------------------------------------

 * Project:      CMSIS DSP Library

 * Title:        arm_rfft_q31.c

 * Description:  FFT & RIFFT Q31 process function

 *

 * $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"

/* ----------------------------------------------------------------------

 * Internal functions prototypes

 * -------------------------------------------------------------------- */

void arm_split_rfft_q31(

    q31_t * pSrc,

    uint32_t fftLen,

    q31_t * pATable,

    q31_t * pBTable,

    q31_t * pDst,

    uint32_t modifier);

void arm_split_rifft_q31(

    q31_t * pSrc,

    uint32_t fftLen,

    q31_t * pATable,

    q31_t * pBTable,

    q31_t * pDst,

    uint32_t modifier);

/**

* @addtogroup RealFFT

* @{

*/

/**

* @brief Processing function for the Q31 RFFT/RIFFT.

* @param[in]  *S    points to an instance of the Q31 RFFT/RIFFT structure.

* @param[in]  *pSrc points to the input buffer.

* @param[out] *pDst points to the output buffer.

* @return none.

*

* \par Input an output formats:

* \par

* Internally input is downscaled by 2 for every stage to avoid saturations inside CFFT/CIFFT process.

* Hence the output format is different for different RFFT sizes.

* The input and output formats for different RFFT sizes and number of bits to upscale are mentioned in the tables below for RFFT and RIFFT:

* \par

* \image html RFFTQ31.gif "Input and Output Formats for Q31 RFFT"

*

* \par

* \image html RIFFTQ31.gif "Input and Output Formats for Q31 RIFFT"

*/

void arm_rfft_q31(

    const arm_rfft_instance_q31 * S,

    q31_t * pSrc,

    q31_t * pDst)

{

    const arm_cfft_instance_q31 *S_CFFT = S->pCfft;

    uint32_t i;

    uint32_t L2 = S->fftLenReal >> 1;

    /* Calculation of RIFFT of input */

    if (S->ifftFlagR == 1U)

    {

        /*  Real IFFT core process */

        arm_split_rifft_q31(pSrc, L2, S->pTwiddleAReal,

                            S->pTwiddleBReal, pDst, S->twidCoefRModifier);

        /* Complex IFFT process */

        arm_cfft_q31(S_CFFT, pDst, S->ifftFlagR, S->bitReverseFlagR);

        for(i=0;i<S->fftLenReal;i++)

        {

            pDst[i] = pDst[i] << 1;

        }

    }

    else

    {

        /* Calculation of RFFT of input */

        /* Complex FFT process */

        arm_cfft_q31(S_CFFT, pSrc, S->ifftFlagR, S->bitReverseFlagR);

        /*  Real FFT core process */

        arm_split_rfft_q31(pSrc, L2, S->pTwiddleAReal,

                            S->pTwiddleBReal, pDst, S->twidCoefRModifier);

    }

}

/**

* @} end of RealFFT group

*/

/**

* @brief  Core Real FFT process

* @param[in]   *pSrc                            points to the input buffer.

* @param[in]   fftLen                       length of FFT.

* @param[in]   *pATable                         points to the twiddle Coef A buffer.

* @param[in]   *pBTable                         points to the twiddle Coef B buffer.

* @param[out]  *pDst                            points to the 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_q31(

    q31_t * pSrc,

    uint32_t fftLen,

    q31_t * pATable,

    q31_t * pBTable,

    q31_t * pDst,

    uint32_t modifier)

{

    uint32_t i;                                    /* Loop Counter */

    q31_t outR, outI;                              /* Temporary variables for output */

    q31_t *pCoefA, *pCoefB;                        /* Temporary pointers for twiddle factors */

    q31_t CoefA1, CoefA2, CoefB1;                  /* Temporary variables for twiddle coefficients */

    q31_t *pOut1 = &pDst[2], *pOut2 = &pDst[(4U * fftLen) - 1U];

    q31_t *pIn1 = &pSrc[2], *pIn2 = &pSrc[(2U * fftLen) - 1U];

    /* Init coefficient pointers */

    pCoefA = &pATable[modifier * 2U];

    pCoefB = &pBTable[modifier * 2U];

    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]); */

        CoefA1 = *pCoefA++;

        CoefA2 = *pCoefA;

        /* outR = (pSrc[2 * i] * pATable[2 * i] */

        mult_32x32_keep32_R(outR, *pIn1, CoefA1);

        /* outI = pIn[2 * i] * pATable[2 * i + 1] */

        mult_32x32_keep32_R(outI, *pIn1++, CoefA2);

        /* - pSrc[2 * i + 1] * pATable[2 * i + 1] */

        multSub_32x32_keep32_R(outR, *pIn1, CoefA2);

        /* (pIn[2 * i + 1] * pATable[2 * i] */

        multAcc_32x32_keep32_R(outI, *pIn1++, CoefA1);

        /* pSrc[2 * n - 2 * i] * pBTable[2 * i]  */

        multSub_32x32_keep32_R(outR, *pIn2, CoefA2);

        CoefB1 = *pCoefB;

        /* pIn[2 * n - 2 * i] * pBTable[2 * i + 1] */

        multSub_32x32_keep32_R(outI, *pIn2--, CoefB1);

        /* pSrc[2 * n - 2 * i + 1] * pBTable[2 * i + 1] */

        multAcc_32x32_keep32_R(outR, *pIn2, CoefB1);

        /* pIn[2 * n - 2 * i + 1] * pBTable[2 * i] */

        multSub_32x32_keep32_R(outI, *pIn2--, CoefA2);

        /* write output */

        *pOut1++ = outR;

        *pOut1++ = outI;

        /* write complex conjugate output */

        *pOut2-- = -outI;

        *pOut2-- = outR;

        /* update coefficient pointer */

        pCoefB = pCoefB + (modifier * 2U);

        pCoefA = pCoefA + ((modifier * 2U) - 1U);

        i--;

    }

    pDst[2U * fftLen] = (pSrc[0] - pSrc[1]) >> 1;

    pDst[(2U * fftLen) + 1U] = 0;

    pDst[0] = (pSrc[0] + pSrc[1]) >> 1;

    pDst[1] = 0;

}

/**

* @brief  Core Real IFFT process

* @param[in]   *pSrc                            points to the input buffer.

* @param[in]   fftLen                       length of FFT.

* @param[in]   *pATable                         points to the twiddle Coef A buffer.

* @param[in]   *pBTable                         points to the twiddle Coef B buffer.

* @param[out]  *pDst                            points to the 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_q31(

    q31_t * pSrc,

    uint32_t fftLen,

    q31_t * pATable,

    q31_t * pBTable,

    q31_t * pDst,

    uint32_t modifier)

{

    q31_t outR, outI;                              /* Temporary variables for output */

    q31_t *pCoefA, *pCoefB;                        /* Temporary pointers for twiddle factors */

    q31_t CoefA1, CoefA2, CoefB1;                  /* Temporary variables for twiddle coefficients */

    q31_t *pIn1 = &pSrc[0], *pIn2 = &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 = (pIn[2 * i] * pATable[2 * i] */

        mult_32x32_keep32_R(outR, *pIn1, CoefA1);

        /* - pIn[2 * i] * pATable[2 * i + 1] */

        mult_32x32_keep32_R(outI, *pIn1++, -CoefA2);

        /* pIn[2 * i + 1] * pATable[2 * i + 1] */

        multAcc_32x32_keep32_R(outR, *pIn1, CoefA2);

        /* pIn[2 * i + 1] * pATable[2 * i] */

        multAcc_32x32_keep32_R(outI, *pIn1++, CoefA1);

        /* pIn[2 * n - 2 * i] * pBTable[2 * i] */

        multAcc_32x32_keep32_R(outR, *pIn2, CoefA2);

        CoefB1 = *pCoefB;

        /* pIn[2 * n - 2 * i] * pBTable[2 * i + 1] */

        multSub_32x32_keep32_R(outI, *pIn2--, CoefB1);

        /* pIn[2 * n - 2 * i + 1] * pBTable[2 * i + 1] */

        multAcc_32x32_keep32_R(outR, *pIn2, CoefB1);

        /* pIn[2 * n - 2 * i + 1] * pBTable[2 * i] */

        multAcc_32x32_keep32_R(outI, *pIn2--, CoefA2);

        /* write output */

        *pDst++ = outR;

        *pDst++ = outI;

        /* update coefficient pointer */

        pCoefB = pCoefB + (modifier * 2U);

        pCoefA = pCoefA + ((modifier * 2U) - 1U);

        /* Decrement loop count */

        fftLen--;

    }

}