arm_bitreversal.c

/* ----------------------------------------------------------------------    
* Copyright (C) 2010-2014 ARM Limited. All rights reserved.    
*    
* $Date:        19. March 2015 
* $Revision: 	V.1.4.5  
*    
* Project: 	    CMSIS DSP Library    
* Title:	    arm_bitreversal.c    
*    
* Description:	This file has common tables like Bitreverse, reciprocal etc which are used across different functions    
*    
* Target Processor: Cortex-M4/Cortex-M3/Cortex-M0
*  
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*   - Redistributions in binary form must reproduce the above copyright
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*     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
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* -------------------------------------------------------------------- */

#include "arm_math.h"
#include "arm_common_tables.h"

/*    
* @brief  In-place bit reversal function.   
* @param[in, out] *pSrc        points to the in-place buffer of floating-point data type.   
* @param[in]      fftSize      length of the FFT.   
* @param[in]      bitRevFactor bit reversal modifier that supports different size FFTs with the same bit reversal table.   
* @param[in]      *pBitRevTab  points to the bit reversal table.   
* @return none.   
*/

void arm_bitreversal_f32(
float32_t * pSrc,
uint16_t fftSize,
uint16_t bitRevFactor,
uint16_t * pBitRevTab)
{
   uint16_t fftLenBy2, fftLenBy2p1;
   uint16_t i, j;
   float32_t in;

   /*  Initializations */
   j = 0u;
   fftLenBy2 = fftSize >> 1u;
   fftLenBy2p1 = (fftSize >> 1u) + 1u;

   /* Bit Reversal Implementation */
   for (i = 0u; i <= (fftLenBy2 - 2u); i += 2u)
   {
      if(i < j)
      {
         /*  pSrc[i] <-> pSrc[j]; */
         in = pSrc[2u * i];
         pSrc[2u * i] = pSrc[2u * j];
         pSrc[2u * j] = in;

         /*  pSrc[i+1u] <-> pSrc[j+1u] */
         in = pSrc[(2u * i) + 1u];
         pSrc[(2u * i) + 1u] = pSrc[(2u * j) + 1u];
         pSrc[(2u * j) + 1u] = in;

         /*  pSrc[i+fftLenBy2p1] <-> pSrc[j+fftLenBy2p1] */
         in = pSrc[2u * (i + fftLenBy2p1)];
         pSrc[2u * (i + fftLenBy2p1)] = pSrc[2u * (j + fftLenBy2p1)];
         pSrc[2u * (j + fftLenBy2p1)] = in;

         /*  pSrc[i+fftLenBy2p1+1u] <-> pSrc[j+fftLenBy2p1+1u] */
         in = pSrc[(2u * (i + fftLenBy2p1)) + 1u];
         pSrc[(2u * (i + fftLenBy2p1)) + 1u] =
         pSrc[(2u * (j + fftLenBy2p1)) + 1u];
         pSrc[(2u * (j + fftLenBy2p1)) + 1u] = in;

      }

      /*  pSrc[i+1u] <-> pSrc[j+1u] */
      in = pSrc[2u * (i + 1u)];
      pSrc[2u * (i + 1u)] = pSrc[2u * (j + fftLenBy2)];
      pSrc[2u * (j + fftLenBy2)] = in;

      /*  pSrc[i+2u] <-> pSrc[j+2u] */
      in = pSrc[(2u * (i + 1u)) + 1u];
      pSrc[(2u * (i + 1u)) + 1u] = pSrc[(2u * (j + fftLenBy2)) + 1u];
      pSrc[(2u * (j + fftLenBy2)) + 1u] = in;

      /*  Reading the index for the bit reversal */
      j = *pBitRevTab;

      /*  Updating the bit reversal index depending on the fft length  */
      pBitRevTab += bitRevFactor;
   }
}



/*    
* @brief  In-place bit reversal function.   
* @param[in, out] *pSrc        points to the in-place buffer of Q31 data type.   
* @param[in]      fftLen       length of the FFT.   
* @param[in]      bitRevFactor bit reversal modifier that supports different size FFTs with the same bit reversal table   
* @param[in]      *pBitRevTab  points to bit reversal table.   
* @return none.   
*/

void arm_bitreversal_q31(
q31_t * pSrc,
uint32_t fftLen,
uint16_t bitRevFactor,
uint16_t * pBitRevTable)
{
   uint32_t fftLenBy2, fftLenBy2p1, i, j;
   q31_t in;

   /*  Initializations      */
   j = 0u;
   fftLenBy2 = fftLen / 2u;
   fftLenBy2p1 = (fftLen / 2u) + 1u;

   /* Bit Reversal Implementation */
   for (i = 0u; i <= (fftLenBy2 - 2u); i += 2u)
   {
      if(i < j)
      {
         /*  pSrc[i] <-> pSrc[j]; */
         in = pSrc[2u * i];
         pSrc[2u * i] = pSrc[2u * j];
         pSrc[2u * j] = in;

         /*  pSrc[i+1u] <-> pSrc[j+1u] */
         in = pSrc[(2u * i) + 1u];
         pSrc[(2u * i) + 1u] = pSrc[(2u * j) + 1u];
         pSrc[(2u * j) + 1u] = in;

         /*  pSrc[i+fftLenBy2p1] <-> pSrc[j+fftLenBy2p1] */
         in = pSrc[2u * (i + fftLenBy2p1)];
         pSrc[2u * (i + fftLenBy2p1)] = pSrc[2u * (j + fftLenBy2p1)];
         pSrc[2u * (j + fftLenBy2p1)] = in;

         /*  pSrc[i+fftLenBy2p1+1u] <-> pSrc[j+fftLenBy2p1+1u] */
         in = pSrc[(2u * (i + fftLenBy2p1)) + 1u];
         pSrc[(2u * (i + fftLenBy2p1)) + 1u] =
         pSrc[(2u * (j + fftLenBy2p1)) + 1u];
         pSrc[(2u * (j + fftLenBy2p1)) + 1u] = in;

      }

      /*  pSrc[i+1u] <-> pSrc[j+1u] */
      in = pSrc[2u * (i + 1u)];
      pSrc[2u * (i + 1u)] = pSrc[2u * (j + fftLenBy2)];
      pSrc[2u * (j + fftLenBy2)] = in;

      /*  pSrc[i+2u] <-> pSrc[j+2u] */
      in = pSrc[(2u * (i + 1u)) + 1u];
      pSrc[(2u * (i + 1u)) + 1u] = pSrc[(2u * (j + fftLenBy2)) + 1u];
      pSrc[(2u * (j + fftLenBy2)) + 1u] = in;

      /*  Reading the index for the bit reversal */
      j = *pBitRevTable;

      /*  Updating the bit reversal index depending on the fft length */
      pBitRevTable += bitRevFactor;
   }
}



/*    
   * @brief  In-place bit reversal function.   
   * @param[in, out] *pSrc        points to the in-place buffer of Q15 data type.   
   * @param[in]      fftLen       length of the FFT.   
   * @param[in]      bitRevFactor bit reversal modifier that supports different size FFTs with the same bit reversal table   
   * @param[in]      *pBitRevTab  points to bit reversal table.   
   * @return none.   
*/

void arm_bitreversal_q15(
q15_t * pSrc16,
uint32_t fftLen,
uint16_t bitRevFactor,
uint16_t * pBitRevTab)
{
   q31_t *pSrc = (q31_t *) pSrc16;
   q31_t in;
   uint32_t fftLenBy2, fftLenBy2p1;
   uint32_t i, j;

   /*  Initializations */
   j = 0u;
   fftLenBy2 = fftLen / 2u;
   fftLenBy2p1 = (fftLen / 2u) + 1u;

   /* Bit Reversal Implementation */
   for (i = 0u; i <= (fftLenBy2 - 2u); i += 2u)
   {
      if(i < j)
      {
         /*  pSrc[i] <-> pSrc[j]; */
         /*  pSrc[i+1u] <-> pSrc[j+1u] */
         in = pSrc[i];
         pSrc[i] = pSrc[j];
         pSrc[j] = in;

         /*  pSrc[i + fftLenBy2p1] <-> pSrc[j + fftLenBy2p1];  */
         /*  pSrc[i + fftLenBy2p1+1u] <-> pSrc[j + fftLenBy2p1+1u] */
         in = pSrc[i + fftLenBy2p1];
         pSrc[i + fftLenBy2p1] = pSrc[j + fftLenBy2p1];
         pSrc[j + fftLenBy2p1] = in;
      }

      /*  pSrc[i+1u] <-> pSrc[j+fftLenBy2];         */
      /*  pSrc[i+2] <-> pSrc[j+fftLenBy2+1u]  */
      in = pSrc[i + 1u];
      pSrc[i + 1u] = pSrc[j + fftLenBy2];
      pSrc[j + fftLenBy2] = in;

      /*  Reading the index for the bit reversal */
      j = *pBitRevTab;

      /*  Updating the bit reversal index depending on the fft length  */
      pBitRevTab += bitRevFactor;
   }
}