text: /* ----------------------------------------------------------------------
  * Copyright (C) 2010-2014 ARM Limited. All rights reserved.
  *
  * $Date: 16/10/14 6:02p $Revision:  V.1.4.5
  *
  * Project:      CMSIS DSP Library
  * Title:        arm_cfft_q31.c
  *
  * Description:  Combined Radix Decimation in Frequency CFFT fixed point processing function
  *
  * Target Processor: Cortex-M4/Cortex-M3/Cortex-M0
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *   - Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
  *   - Redistributions in binary form must reproduce the above copyright
  *     notice, this list of conditions and the following disclaimer in
  *     the documentation and/or other materials provided with the
  *     distribution.
  *   - Neither the name of ARM LIMITED nor the names of its contributors
  *     may be used to endorse or promote products derived from this
  *     software without specific prior written permission.
  *
  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
  * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
  * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
  * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
  * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
  * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
  * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
  * POSSIBILITY OF SUCH DAMAGE.
  * -------------------------------------------------------------------- */
  
  #include "arm_math.h"
  
  extern void arm_radix4_butterfly_q31(
      q31_t * pSrc,
      uint32_t fftLen,
      q31_t * pCoef,
      uint32_t twidCoefModifier);
  
  extern void arm_radix4_butterfly_inverse_q31(
      q31_t * pSrc,
      uint32_t fftLen,
      q31_t * pCoef,
      uint32_t twidCoefModifier);
  
  extern void arm_bitreversal_32(
      uint32_t * pSrc,
      const uint16_t bitRevLen,
      const uint16_t * pBitRevTable);
  
  void arm_cfft_radix4by2_q31(
      q31_t * pSrc,
      uint32_t fftLen,
      const q31_t * pCoef);
  
  void arm_cfft_radix4by2_inverse_q31(
      q31_t * pSrc,
      uint32_t fftLen,
      const q31_t * pCoef);
  
  /**
  * @ingroup groupTransforms
  */
  
  /**
  * @addtogroup ComplexFFT
  * @{
  */
  
  /**
  * @details
  * @brief       Processing function for the fixed-point complex FFT in Q31 format.
  * @param[in]      *S    points to an instance of the fixed-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 forward (ifftFlag=0) or inverse (ifftFlag=1) transform.
  * @param[in]     bitReverseFlag flag that enables (bitReverseFlag=1) or disables (bitReverseFlag=0) bit reversal of output.
  * @return none.
  */
  
  void arm_cfft_q31(
      const arm_cfft_instance_q31 * S,
      q31_t * p1,
      uint8_t ifftFlag,
      uint8_t bitReverseFlag)
  {
      uint32_t L = S->fftLen;
  
      if(ifftFlag == 1u)
      {
          switch(L)
          {
              case 16:
              case 64:
              case 256:
              case 1024:
              case 4096:
                  arm_radix4_butterfly_inverse_q31(p1, L, (q31_t*)S->pTwiddle, 1);
                  break;
  
              case 32:
              case 128:
              case 512:
              case 2048:
                  arm_cfft_radix4by2_inverse_q31(p1, L, S->pTwiddle);
                  break;
          }
      }
      else
      {
          switch(L)
          {
              case 16:
              case 64:
              case 256:
              case 1024:
              case 4096:
                  arm_radix4_butterfly_q31(p1, L, (q31_t*)S->pTwiddle, 1);
                  break;
  
              case 32:
              case 128:
              case 512:
              case 2048:
                  arm_cfft_radix4by2_q31(p1, L, S->pTwiddle);
                  break;
          }
      }
  
      if(bitReverseFlag)
          arm_bitreversal_32((uint32_t*)p1, S->bitRevLength, S->pBitRevTable);
  }
  
  /**
  * @} end of ComplexFFT group
  */
  
  void arm_cfft_radix4by2_q31(
      q31_t * pSrc,
      uint32_t fftLen,
      const q31_t * pCoef)
  {
      uint32_t i, l;
      uint32_t n2, ia;
      q31_t xt, yt, cosVal, sinVal;
      q31_t p0, p1;
  
      n2 = fftLen >> 1;
      ia = 0;
      for(i = 0; i < n2; i++)
      {
          cosVal = pCoef[2 * ia];
          sinVal = pCoef[2 * ia + 1];
          ia++;
  
          l = i + n2;
          xt = (pSrc[2 * i] >> 2) - (pSrc[2 * l] >> 2);
          pSrc[2 * i] = (pSrc[2 * i] >> 2) + (pSrc[2 * l] >> 2);
  
          yt = (pSrc[2 * i + 1] >> 2) - (pSrc[2 * l + 1] >> 2);
          pSrc[2 * i + 1] = (pSrc[2 * l + 1] >> 2) + (pSrc[2 * i + 1] >> 2);
  
          mult_32x32_keep32_R(p0, xt, cosVal);
          mult_32x32_keep32_R(p1, yt, cosVal);
          multAcc_32x32_keep32_R(p0, yt, sinVal);
          multSub_32x32_keep32_R(p1, xt, sinVal);
  
          pSrc[2u * l] = p0 << 1;
          pSrc[2u * l + 1u] = p1 << 1;
  
      }
  
      // first col
      arm_radix4_butterfly_q31(pSrc, n2, (q31_t*)pCoef, 2u);
      // second col
      arm_radix4_butterfly_q31(pSrc + fftLen, n2, (q31_t*)pCoef, 2u);
  
      for(i = 0; i < fftLen >> 1; i++)
      {
          p0 = pSrc[4 * i + 0];
          p1 = pSrc[4 * i + 1];
          xt = pSrc[4 * i + 2];
          yt = pSrc[4 * i + 3];
  
          p0 <<= 1;
          p1 <<= 1;
          xt <<= 1;
          yt <<= 1;
  
          pSrc[4 * i + 0] = p0;
          pSrc[4 * i + 1] = p1;
          pSrc[4 * i + 2] = xt;
          pSrc[4 * i + 3] = yt;
      }
  
  }
  
  void arm_cfft_radix4by2_inverse_q31(
      q31_t * pSrc,
      uint32_t fftLen,
      const q31_t * pCoef)
  {
      uint32_t i, l;
      uint32_t n2, ia;
      q31_t xt, yt, cosVal, sinVal;
      q31_t p0, p1;
  
      n2 = fftLen >> 1;
      ia = 0;
      for(i = 0; i < n2; i++)
      {
          cosVal = pCoef[2 * ia];
          sinVal = pCoef[2 * ia + 1];
          ia++;
  
          l = i + n2;
          xt = (pSrc[2 * i] >> 2) - (pSrc[2 * l] >> 2);
          pSrc[2 * i] = (pSrc[2 * i] >> 2) + (pSrc[2 * l] >> 2);
  
          yt = (pSrc[2 * i + 1] >> 2) - (pSrc[2 * l + 1] >> 2);
          pSrc[2 * i + 1] = (pSrc[2 * l + 1] >> 2) + (pSrc[2 * i + 1] >> 2);
  
          mult_32x32_keep32_R(p0, xt, cosVal);
          mult_32x32_keep32_R(p1, yt, cosVal);
          multSub_32x32_keep32_R(p0, yt, sinVal);
          multAcc_32x32_keep32_R(p1, xt, sinVal);
  
          pSrc[2u * l] = p0 << 1;
          pSrc[2u * l + 1u] = p1 << 1;
  
      }
  
      // first col
      arm_radix4_butterfly_inverse_q31(pSrc, n2, (q31_t*)pCoef, 2u);
      // second col
      arm_radix4_butterfly_inverse_q31(pSrc + fftLen, n2, (q31_t*)pCoef, 2u);
  
      for(i = 0; i < fftLen >> 1; i++)
      {
          p0 = pSrc[4 * i + 0];
          p1 = pSrc[4 * i + 1];
          xt = pSrc[4 * i + 2];
          yt = pSrc[4 * i + 3];
  
          p0 <<= 1;
          p1 <<= 1;
          xt <<= 1;
          yt <<= 1;
  
          pSrc[4 * i + 0] = p0;
          pSrc[4 * i + 1] = p1;
          pSrc[4 * i + 2] = xt;
          pSrc[4 * i + 3] = yt;
      }
  }
  
  