bit_reverse.c

来自「基于8051F单片机,实现1024点的FFT 用C 语言实现的.效果与FPGA」· C语言 代码 · 共 51 行

#include "FFT_Code_Tables.h"
//-----------------------------------------------------------------------------
// Bit_Reverse
//-----------------------------------------------------------------------------
//
// Sorts data in Bit Reversed Address order
//
// The BRTable[] array is used to find which values must be swapped.  Only
// half of this array is stored, to save code space.  The second half is
// assumed to be a mirror image of the first half.
//
void Bit_Reverse(int BR_Array[])
{

#if (NUM_FFT >= 512)
unsigned int swapA, swapB, sw_cnt;           // Swap Indices
#endif

#if (NUM_FFT <= 256)
unsigned char swapA, swapB, sw_cnt;          // Swap Indices
#endif

int TempStore;

   // Loop through locations to swap
   for (sw_cnt = 1; sw_cnt < NUM_FFT/2; sw_cnt++)
   {
      swapA = sw_cnt;                        // Store current location
      swapB = BRTable[sw_cnt] * 2;           // Retrieve bit-reversed index
      if (swapB > swapA)                     // If the bit-reversed index is

      {                                      // larger than the current index,
         TempStore = BR_Array[swapA];        // the two data locations are
         BR_Array[swapA] = BR_Array[swapB];  // swapped. Using this comparison
         BR_Array[swapB] = TempStore;        // ensures that locations are only
      }                                      // swapped once, and never with
                                             // themselves

      swapA += NUM_FFT/2;                    // Now perform the same operations
      swapB++;                               // on the second half of the data
      if (swapB > swapA)
      {
         TempStore = BR_Array[swapA];
         BR_Array[swapA] = BR_Array[swapB];
         BR_Array[swapB] = TempStore;
      }
   }

}  // END Bit Reverse Order Sort