Re: "A diagram of C23 basic types"

Janis Papanagnou <janis_papanagnou+ng@hotmail.com> writes:

On 27.06.2025 02:10, Keith Thompson wrote:

scott@slp53.sl.home (Scott Lurndal) writes:
[...]

But not all decimal floating point implementations used "hex floating point".
>
Burroughs medium systems had BCD floating point - one of the advantages
was that it could exactly represent any floating point number that
could be specified with a 100 digit mantissa and a 2 digit exponent.

 
BCD uses 4 bits to represent values from 0 to 9.  That's about 83%
efficent relative to pure binary.  (And it still can't represent 1/3.)

>
That's a problem of where your numbers stem from. "1/3" is a formula!

1/3 is also a C expression with the value 0.  But what I was
referring to was the real number 1/3, the unique real number that
yields one when multiplied by three.

My point is that any choice of radix in a floating-point format
means that there are going to be some useful real numbers you
can't represent.  That's as true of decimal as it is of binary.
(Trinary can represent 1/3, but can't represent 1/2.)

Decimal can represent any number that can be exactly represented in
binary *if* you have enough digits (because 10 is multiple of 2),
and many numbers like 0.1 that can't be represented exactly in
binary, but at a cost -- that is worth paying in some contexts.
(Scaled integers might sometimes be a good alternative).

I doubt that I'm saying anything you don't already know.  I just
wanted to clarify what I meant.

[...]

--
Keith Thompson (The_Other_Keith) Keith.S.Thompson+u@gmail.com
void Void(void) { Void(); } /* The recursive call of the void */