DSP/Source/TransformFunctions/arm_rfft_q31.c

/* ----------------------------------------------------------------------
 * 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--;
    }
}