Re: fixed point vs floating point

[dewar@merv.cs.nyu.edu (Robert Dewar)]

Tuck said

<<I'm not sure to what Robert is referring here.  Fixed + fixed is
as efficient as the normal integer operation, as is Fixed - Fixed,
Fixed * Integer, and Fixed / Integer.  The only operations that are
potentially inefficient are Fixed * Fixed and Fixed / Fixed, neither of which
are particularly likely when the fixed-point type represents an angle ;-).

Even if you do use Fixed * Fixed or Fixed / Fixed, the inefficiency
has to do with sometimes having to shift the result or one of the
operands after/before performing the operation (presuming binary
smalls).  If the machine has efficient shifting, this is not a major
overhead.  However, it may be that on some compilers, the fixed-fixed
multiplication/division operations are handled out-of-line, and the
procedure-call overhead is the primary added expense.
>>

Surely Tuck, you know that on almost all modern machines, integer
multiplication is much slower than floating-point multiplication?

So even without the sift, you are behind.

Sure if you never do multiplications, then the penalty for fixed-point
can be close to zero (compared with flaoting-point), unless of course
you want more than 32 bits of precision and you are on a 32 bit machine,
then fixed-point gets very expensive.