DSP/Source/TransformFunctions/arm_bitreversal2.c

/* ----------------------------------------------------------------------
 * Project:      CMSIS DSP Library
 * Title:        arm_bitreversal2.c
 * Description:  Bitreversal functions
 *
 * $Date:        18. March 2019
 * $Revision:    V1.0.0
 *
 * Target Processor: Cortex-M cores
 * -------------------------------------------------------------------- */
/*
 * Copyright (C) 2019 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"
#include "arm_common_tables.h"

/**
  @brief         In-place 32 bit reversal function.
  @param[in,out] pSrc        points to in-place buffer of unknown 32-bit data type
  @param[in]     bitRevLen   bit reversal table length
  @param[in]     pBitRevTab  points to bit reversal table
  @return        none
*/

void arm_bitreversal_32(
        uint32_t *pSrc, 
  const uint16_t bitRevLen, 
  const uint16_t *pBitRevTab)
{
  uint32_t a, b, i, tmp;

  for (i = 0; i < bitRevLen; )
  {
     a = pBitRevTab[i    ] >> 2;
     b = pBitRevTab[i + 1] >> 2;

     //real
     tmp = pSrc[a];
     pSrc[a] = pSrc[b];
     pSrc[b] = tmp;

     //complex
     tmp = pSrc[a+1];
     pSrc[a+1] = pSrc[b+1];
     pSrc[b+1] = tmp;

    i += 2;
  }
}


/**
  @brief         In-place 16 bit reversal function.
  @param[in,out] pSrc        points to in-place buffer of unknown 16-bit data type
  @param[in]     bitRevLen   bit reversal table length
  @param[in]     pBitRevTab  points to bit reversal table
  @return        none
*/

void arm_bitreversal_16(
        uint16_t *pSrc, 
  const uint16_t bitRevLen, 
  const uint16_t *pBitRevTab)
{
  uint16_t a, b, i, tmp;

  for (i = 0; i < bitRevLen; )
  {
     a = pBitRevTab[i    ] >> 2;
     b = pBitRevTab[i + 1] >> 2;

     //real
     tmp = pSrc[a];
     pSrc[a] = pSrc[b];
     pSrc[b] = tmp;

     //complex
     tmp = pSrc[a+1];
     pSrc[a+1] = pSrc[b+1];
     pSrc[b+1] = tmp;

    i += 2;
  }
}