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Re: About the bits reserved for float variable [message #39506 is a reply to message #39505]

Fri, 21 May 2004 07:44

Paul Van Delst[1]
Messages: 1157
Registered: April 2002

Senior Member

Nuno Oliveira wrote:
> I looking at the Chapter 5 of the Bulding Aplication.
>
> It says, for float variables that it's a 32 bits number in the range of
> +/-10^38 withe approximately six or seven decimal places of significance.
> What I'm missing here? How can a number 32 bit number range between -10^38
> and +10^38?

Some of the bits are used for the significand, and some of the bits are used for the
exponent. For IEEE 754 arithmetic, a single precision, 32-bit, number uses 23 bits for the
significand (plus one for the sign bit), and 8 for the exponent. With 8 bits for the
exponent, it can range from -127 to 128. 2^-127 ~ 10^-38, 2^128 ~ 10^38.

Similarly for double precision (64 bit) where the significand is 52 bits long and the
exponent 11 bits giving a range of ~10^(+/-)308.

Don't quote anything I've said above as being anything other than a 2-bit (ha ha)
explanation of a somewhat complicated topic by someone (me) who only understands the very
basics.

paulv

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[Message index]

		Re: About the bits reserved for float variable By: George N. White III on Sat, 22 May 2004 05:01
		Re: About the bits reserved for float variable By: Kenneth P. Bowman on Fri, 21 May 2004 15:22
		Re: About the bits reserved for float variable By: David Fanning on Fri, 21 May 2004 08:07
		Re: About the bits reserved for float variable By: James Kuyper on Fri, 21 May 2004 08:00
		Re: About the bits reserved for float variable By: Paul Van Delst[1] on Fri, 21 May 2004 07:44
		Re: About the bits reserved for float variable By: Chris Lee on Fri, 21 May 2004 07:36
		Re: About the bits reserved for float variable By: Nuno Oliveira on Tue, 25 May 2004 10:08

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