23 Oct
2011
23 Oct
'11
6:32 p.m.
On Oct 23, 2011, at 9:04 PM, Chuck Guzis wrote:
Regardless, I was referring to the old, almost
forgotten "floating
decimal point" sometimes found on old calculators and in early
computer programs. There, the point moves anywhere within the
significand, but not outside of it.
For example, if you have a 4 digit device, a floating point can
express values between .0001 and 9999. No exponent to extend the
range of absolute values. Fixed point, in the same sense only means
that the decimal point is anchored to a particular position; e.g.,
12.34 is a fixed-point number with the point fixed between the two
high-order digits and the two low-order digits.
But if you're moving the decimal point around, aren't you changing the exponent?
You're just doing it in base 10 instead of base 2. That's why it's called
floating-point - the point can move around.
Typically, fixed-point means you have fixed-size integer and fraction portions. Say, with
dollars, you might have 4 digits of integer and 2 digits of fraction, which would restrict
you to 9999.99. Or in binary, you might have a fixed 24 bits of integer and 8 bits of
fraction. The decimal never moves, in fact it can't (unless you're printing it
out and just don't print all the zeroes at the end).
- Dave