[hpsdr] exact frequency determination

[John Marvin]

Chris,

Are you referring to this part of my explanation:

> This can be reduced to:
>
>      Frequency * 2^16 / 1875
>
> In order to preserve accuracy while doing integer math we shift everything to the left 25 bits, use a nearby integer constant for the multiply and then shift the result back 25 bits:
>
>      (Frequency * 2^41 / 1875) >> 25

If so, I think the confusion might be that I did the left shift by 
changing the 2^16 to 2^41. The two equations are equivalent, since the 
second equation includes both a 25 bit left shift and a 25 bit right shift.

Regards,

John
AC0ZG

On 11/21/2013 3:58 AM, Chris Smith wrote:
> John
>
> Last time I looked in a C or C++ programming manual >> denoted a right shift - divide by 2^n. Unless the integer arithmetic is double length and you're trying to end up with all the bits in the LS half. But then the shift would have to be n-25 where n is the word length in bits. Or should that be 25-n … ?  I can't be bothered to work it out. :-)
>
> Chris G4NUX
>


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