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How to use the proper decimals in 28335?

Jack Qian
Prodigy 115 points

In using 28335 FPU,sometimes I need to use the expression like :

Ualpha=1.0*sqrt(3);

In order to improve the program's efficiency I write the above expression into:

Ualpha=1.0*1.732050808;   //sqrt(3)=1.732050808

but Idon't sure how many decimals should I use in order to get the proper precision (Should I use 1.732051 or 1.732050808 or more decimals)?

P.S.   I use the watch window in CCS3.3 to  see the value of Ualpha=1.0*1.73205080, find that Ualpha=1.732051(only has 6 decimals).

          So,can I say that if I use 28335 FPU,  I only need to use 6 decimals?

Thanks!

  • 0
    TI__Mastermind 43730 points

    Jack,

    The single precision FPU has 23 bits for the mantissa, which means that the maximum value of the mantissa is 2^23 = 8388608, hence you can have 7 significant decimal points, => both decimal and fraction included.

    so for 17.32051 you need to specify only 5 values beyond the fraction point,

    Hope this helps,

    Regards

    Manish Bhardwaj