[TAG added]
On May 31, 2011, at 12:42 AM, William Chops Westfield wrote:

>
> On May 31, 2011, at 12:17 AM, IV3YNB op. Matteo wrote:
>
>> the trouble now comes when I have to manage frequency value
>> and get it in 32bit.
>>
>> The formula is M =3D (f0 * 2^32)/fc
>
> You'll have to re-arrange that formula to get this to work in most C
> compilers (or most other languages), since most values of f0*2^32 will
> exceed 32 bits...
>
> If Fc is 50MHz, you can do (f0 * (2^32/128) / (Fc/128)
> (128 is the greatest common factor of 2^32 and 50e6)
> More math tricks may be needed depending on the range and required
> accuracy of f0, but the general principle is DON'T LET INTERMEDIATE
> RESULTS EXCEED THE VARIABLE SIZE.
>
> BillW

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