1  /* ----------------------------------------------------------------------
  2   * Project:      CMSIS DSP Library
  3   * Title:        arm_bitreversal_f16.c
  4   * Description:  Bitreversal functions
  5   *
  6   * $Date:        23 April 2021
  7   * $Revision:    V1.9.0
  8   *
  9   * Target Processor: Cortex-M and Cortex-A cores
 10   * -------------------------------------------------------------------- */
 11  /*
 12   * Copyright (C) 2010-2021 ARM Limited or its affiliates. All rights reserved.
 13   *
 14   * SPDX-License-Identifier: Apache-2.0
 15   *
 16   * Licensed under the Apache License, Version 2.0 (the License); you may
 17   * not use this file except in compliance with the License.
 18   * You may obtain a copy of the License at
 19   *
 20   * www.apache.org/licenses/LICENSE-2.0
 21   *
 22   * Unless required by applicable law or agreed to in writing, software
 23   * distributed under the License is distributed on an AS IS BASIS, WITHOUT
 24   * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 25   * See the License for the specific language governing permissions and
 26   * limitations under the License.
 27   */
 28  
 29  #include "dsp/transform_functions_f16.h"
 30  
 31  /*
 32  * @brief  In-place bit reversal function.
 33  * @param[in, out] *pSrc        points to the in-place buffer of floating-point data type.
 34  * @param[in]      fftSize      length of the FFT.
 35  * @param[in]      bitRevFactor bit reversal modifier that supports different size FFTs with the same bit reversal table.
 36  * @param[in]      *pBitRevTab  points to the bit reversal table.
 37  * @return none.
 38  */
 39  
 40  #if defined(ARM_FLOAT16_SUPPORTED)
 41  
 42  void arm_bitreversal_f16(
 43  float16_t * pSrc,
 44  uint16_t fftSize,
 45  uint16_t bitRevFactor,
 46  const uint16_t * pBitRevTab)
 47  {
 48     uint16_t fftLenBy2, fftLenBy2p1;
 49     uint16_t i, j;
 50     float16_t in;
 51  
 52     /*  Initializations */
 53     j = 0U;
 54     fftLenBy2 = fftSize >> 1U;
 55     fftLenBy2p1 = (fftSize >> 1U) + 1U;
 56  
 57     /* Bit Reversal Implementation */
 58     for (i = 0U; i <= (fftLenBy2 - 2U); i += 2U)
 59     {
 60        if (i < j)
 61        {
 62           /*  pSrc[i] <-> pSrc[j]; */
 63           in = pSrc[2U * i];
 64           pSrc[2U * i] = pSrc[2U * j];
 65           pSrc[2U * j] = in;
 66  
 67           /*  pSrc[i+1U] <-> pSrc[j+1U] */
 68           in = pSrc[(2U * i) + 1U];
 69           pSrc[(2U * i) + 1U] = pSrc[(2U * j) + 1U];
 70           pSrc[(2U * j) + 1U] = in;
 71  
 72           /*  pSrc[i+fftLenBy2p1] <-> pSrc[j+fftLenBy2p1] */
 73           in = pSrc[2U * (i + fftLenBy2p1)];
 74           pSrc[2U * (i + fftLenBy2p1)] = pSrc[2U * (j + fftLenBy2p1)];
 75           pSrc[2U * (j + fftLenBy2p1)] = in;
 76  
 77           /*  pSrc[i+fftLenBy2p1+1U] <-> pSrc[j+fftLenBy2p1+1U] */
 78           in = pSrc[(2U * (i + fftLenBy2p1)) + 1U];
 79           pSrc[(2U * (i + fftLenBy2p1)) + 1U] =
 80           pSrc[(2U * (j + fftLenBy2p1)) + 1U];
 81           pSrc[(2U * (j + fftLenBy2p1)) + 1U] = in;
 82  
 83        }
 84  
 85        /*  pSrc[i+1U] <-> pSrc[j+1U] */
 86        in = pSrc[2U * (i + 1U)];
 87        pSrc[2U * (i + 1U)] = pSrc[2U * (j + fftLenBy2)];
 88        pSrc[2U * (j + fftLenBy2)] = in;
 89  
 90        /*  pSrc[i+2U] <-> pSrc[j+2U] */
 91        in = pSrc[(2U * (i + 1U)) + 1U];
 92        pSrc[(2U * (i + 1U)) + 1U] = pSrc[(2U * (j + fftLenBy2)) + 1U];
 93        pSrc[(2U * (j + fftLenBy2)) + 1U] = in;
 94  
 95        /*  Reading the index for the bit reversal */
 96        j = *pBitRevTab;
 97  
 98        /*  Updating the bit reversal index depending on the fft length  */
 99        pBitRevTab += bitRevFactor;
100     }
101  }
102  #endif /* #if defined(ARM_FLOAT16_SUPPORTED) */