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From: Charles Hixson <charleshixsn@earthlink.net>
Subject: Re: Disallowing Pre-Defined Operations
Date: 2000/03/17
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Paul Graham wrote:

> Charles Hixson wrote:
> >
> > Re: Units:
> > mks? cgs? or English System? (And is a gallon an Imperial Gallon or a US
> > gallon?)  Are angles measures in degrees, radians, or mils? (etc.)
>
> VHDL has a syntax for defining units for a given physical type.  For
> instance:
>
>     type distance is range integer'left to integer'right
>         units angstrom;
>         nm = 10 angstrom;
>         mm = 1000_000 nm;
>         inch = 25 mm;
>     end units;
>
> Internally a value of a physical type is represented in terms of its
> base unit, in this case angstroms.  This representation is obtained from
> the 'pos attribute.  To convert from one unit to another (e.g., for
> display purposes) you can do:
>
>     variable d : distance;      -- vhdl declaration syntax
>     variable d_inches : integer;
>     variable d_mm : integer;
>
>     d_inches := distance'pos(d) / distance'pos(1 inch);
>     d_mm := distance'pos(d) / distance'pos(1 mm);
>
> It's also possible to combine different units of the same type:
>
>     d := 3 mm + 4 inch + 2 angstrom;
>
> Paul

That would have saved at least one space probe.  (By that here I mean the
automatic conversion of units.)