dsPIC FFT example improvement

[yo2lio]

Hello,

I make an improvement in FFT example.

Instead of this code, in WriteData routine :

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      tmpR := sqrt(Rer + Imr);      // Amplitude of current DFT sample
      Rer  := tmpR*256.;            // DFT is scaled down by 1/N, we need to
                                    //   take it back in order to have visible
                                    //   components on GLCD

      Re := Rer;

I put this code :

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Re := sqrt_int(dword(Rer + Imr)*65536);

Where sqrt_int routine is :

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function sqrt_int(num : dword) : dword;
var one : dword;
begin
  result := 0;
  one := 1 shl 30;
  while one > num do one := one shr 2;
  while one > 0 do
    begin
      if num >= (result + one) then
        begin
          num := num - (result + one);
          result := result + (one shl 1);
        end;
      result := result shr 1;
      one := one shr 2;
    end;
end;

sqrt_int routine, is not my invention, I found this on the Google ....

With this improvement, WriteData routine is 4 time faster !!!

Enjoy !

[SamY Fareast]

GREAT!

But typo?

I put this code :
Code:

Code: Select all

Re := sqrt_int(dword(Rer + Imr)*65536);

By 'Fract2Float' function,
On this timing, 0<= Rer, Imr < 1, then dword(Rer+Imr) is almost 0.

Code: Select all

Re := (Rer + Imr) * 65535;
Re := sqr_int(dword(Re));

May work, But if you use 'sqr_int ' routine, there is no needs for use Real type anymore.

I wrote another modification to 'Write_Data' on http://www.mikroe.com/forum/viewtopic.php?t=18699.
Please check it.