File content as of revision 1:fdd22bb7aa52:

/* ----------------------------------------------------------------------    
* Copyright (C) 2010 ARM Limited. All rights reserved.    
*    
* $Date:        15. February 2012  
* $Revision:     V1.1.0  
*    
* Project:         CMSIS DSP Library    
* Title:        arm_rfft_q31.c    
*    
* Description:    RFFT & RIFFT Q31 process function    
*    
*    
* Target Processor: Cortex-M4/Cortex-M3/Cortex-M0
*  
* Version 1.1.0 2012/02/15 
*    Updated with more optimizations, bug fixes and minor API changes.  
*   
* Version 1.0.10 2011/7/15  
*    Big Endian support added and Merged M0 and M3/M4 Source code.   
*    
* Version 1.0.3 2010/11/29   
*    Re-organized the CMSIS folders and updated documentation.    
*     
* Version 1.0.2 2010/11/11    
*    Documentation updated.     
*    
* Version 1.0.1 2010/10/05     
*    Production release and review comments incorporated.    
*    
* Version 1.0.0 2010/09/20     
*    Production release and review comments incorporated.    
*    
* Version 0.0.7  2010/06/10     
*    Misra-C changes done    
* -------------------------------------------------------------------- */

#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 RFFT_RIFFT    
 * @{    
 */

/**    
 * @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_radix4_instance_q31 *S_CFFT = S->pCfft;

  /* Calculation of RIFFT of input */
  if(S->ifftFlagR == 1u)
  {
    /*  Real IFFT core process */
    arm_split_rifft_q31(pSrc, S->fftLenBy2, S->pTwiddleAReal,
                        S->pTwiddleBReal, pDst, S->twidCoefRModifier);

    /* Complex readix-4 IFFT process */
    arm_radix4_butterfly_inverse_q31(pDst, S_CFFT->fftLen,
                                     S_CFFT->pTwiddle,
                                     S_CFFT->twidCoefModifier);
    /* Bit reversal process */
    if(S->bitReverseFlagR == 1u)
    {
      arm_bitreversal_q31(pDst, S_CFFT->fftLen,
                          S_CFFT->bitRevFactor, S_CFFT->pBitRevTable);
    }
  }
  else
  {
    /* Calculation of RFFT of input */

    /* Complex readix-4 FFT process */
    arm_radix4_butterfly_q31(pSrc, S_CFFT->fftLen,
                             S_CFFT->pTwiddle, S_CFFT->twidCoefModifier);

    /* Bit reversal process */
    if(S->bitReverseFlagR == 1u)
    {
      arm_bitreversal_q31(pSrc, S_CFFT->fftLen,
                          S_CFFT->bitRevFactor, S_CFFT->pBitRevTable);
    }

    /*  Real FFT core process */
    arm_split_rfft_q31(pSrc, S->fftLenBy2, S->pTwiddleAReal,
                       S->pTwiddleBReal, pDst, S->twidCoefRModifier);
  }

}


  /**    
   * @} end of RFFT_RIFFT 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] */
    outR = ((int32_t) (((q63_t) * pIn1 * CoefA1) >> 32));

    /* outI = pIn[2 * i] * pATable[2 * i + 1] */
    outI = ((int32_t) (((q63_t) * pIn1++ * CoefA2) >> 32));

    /* - pSrc[2 * i + 1] * pATable[2 * i + 1] */
    outR =
      (q31_t) ((((q63_t) outR << 32) + ((q63_t) * pIn1 * (-CoefA2))) >> 32);

    /* (pIn[2 * i + 1] * pATable[2 * i] */
    outI =
      (q31_t) ((((q63_t) outI << 32) + ((q63_t) * pIn1++ * (CoefA1))) >> 32);

    /* pSrc[2 * n - 2 * i] * pBTable[2 * i]  */
    outR =
      (q31_t) ((((q63_t) outR << 32) + ((q63_t) * pIn2 * (-CoefA2))) >> 32);
    CoefB1 = *pCoefB;

    /* pIn[2 * n - 2 * i] * pBTable[2 * i + 1] */
    outI =
      (q31_t) ((((q63_t) outI << 32) + ((q63_t) * pIn2-- * (-CoefB1))) >> 32);

    /* pSrc[2 * n - 2 * i + 1] * pBTable[2 * i + 1] */
    outR =
      (q31_t) ((((q63_t) outR << 32) + ((q63_t) * pIn2 * (CoefB1))) >> 32);

    /* pIn[2 * n - 2 * i + 1] * pBTable[2 * i] */
    outI =
      (q31_t) ((((q63_t) outI << 32) + ((q63_t) * pIn2-- * (-CoefA2))) >> 32);

    /* write output */
    *pOut1++ = (outR << 1u);
    *pOut1++ = (outI << 1u);

    /* write complex conjugate output */
    *pOut2-- = -(outI << 1u);
    *pOut2-- = (outR << 1u);

    /* 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;

  pDst[0] = pSrc[0] + pSrc[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] */
    outR = ((int32_t) (((q63_t) * pIn1 * CoefA1) >> 32));

    /* - pIn[2 * i] * pATable[2 * i + 1] */
    outI = -((int32_t) (((q63_t) * pIn1++ * CoefA2) >> 32));

    /* pIn[2 * i + 1] * pATable[2 * i + 1] */
    outR =
      (q31_t) ((((q63_t) outR << 32) + ((q63_t) * pIn1 * (CoefA2))) >> 32);

    /* pIn[2 * i + 1] * pATable[2 * i] */
    outI =
      (q31_t) ((((q63_t) outI << 32) + ((q63_t) * pIn1++ * (CoefA1))) >> 32);

    /* pIn[2 * n - 2 * i] * pBTable[2 * i] */
    outR =
      (q31_t) ((((q63_t) outR << 32) + ((q63_t) * pIn2 * (CoefA2))) >> 32);

    CoefB1 = *pCoefB;

    /* pIn[2 * n - 2 * i] * pBTable[2 * i + 1] */
    outI =
      (q31_t) ((((q63_t) outI << 32) - ((q63_t) * pIn2-- * (CoefB1))) >> 32);

    /* pIn[2 * n - 2 * i + 1] * pBTable[2 * i + 1] */
    outR =
      (q31_t) ((((q63_t) outR << 32) + ((q63_t) * pIn2 * (CoefB1))) >> 32);

    /* pIn[2 * n - 2 * i + 1] * pBTable[2 * i] */
    outI =
      (q31_t) ((((q63_t) outI << 32) + ((q63_t) * pIn2-- * (CoefA2))) >> 32);

    /* write output */
    *pDst++ = (outR << 1u);
    *pDst++ = (outI << 1u);

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

    /* Decrement loop count */
    fftLen--;

  }


}