OpenEuphoria

Re: Hexadecimal numbers in Eu

• Posted by "Unkmar" <L3Euphoria at bellsouth.net> Sep 20, 2004
• 421 views

----- Original Message -----
From: "Derek Parnell" <guest at RapidEuphoria.com>
To: <EUforum at topica.com>
Sent: Sunday, September 19, 2004 10:42 AM
Subject: Re: Hexadecimal numbers in Eu


>
>
> posted by: Derek Parnell <ddparnell at bigpond.com>
>
> Juergen Luethje wrote:
> >
> > Robert Craig wrote:
> >
> > > Juergen Luethje wrote:
> > >>
> > >> Derek Parnell wrote:
> > >>
> > >>> Juergen Luethje wrote:
> > >>>>
> > >>>> Hi,
> > >>>>
> > >>>> in some other programming languages, hex numbers can represent
positive
> > >>>> or negative values. E.g. in PowerBASIC 3.2,
> > >>>>    ? &hFFF0       ' prints -16
> > >>>>    ? &h00F0       ' prints 240
> > >>>>
> > >>>>> From what I read at 'refman_2.htm#1' (Eu 2.4), and from my
experience,
> > >>>> I have the impression that hexadecimal numbers (that don't have a
'-'
> > >>>> sign at the beginning) in Euphoria _always_ have positive values.
> > >>>>
> > >>>> Rob, is this true?
> > >>>>
> > >>>> In Euphoria, e.g.
> > >>>> }}}
<eucode>
> > >>>>    ? #FFF0       -- prints 65520
> > >>>>    ? #00F0       -- prints 240
> > >>>> </eucode>
{{{

> > >>>
> > >>>
> > >>> Yes, hexadecimal literals are always positive unless they have a
leading
> > >>> minus symbol.
> > >>
> > >> Rob, maybe this sentence could be added to the docs? I think it will
be
> > >> very helpful for beginners -- and people like me, who sometimes feel
> > >> like beginners. 
> > >
> > > OK, I'll say something in the docs about this.
> >
> > Thanks, that will eliminate ambiguity.
> >
> > >>> However it is a bit confusing because negative integers, when
converted
> > >>> to display as hex digits via the printf() routine, display without
> > >>> the minus sign.
> > >>>
> > >>> printf(1, "%x", -1)  --> FFFFFFFF
> > >>
> > >> Yes, this actually confused me some days ago!! Thanks, Derek!
> > >>
> > >> Rob, is there any chance that in a future version of Euphoria,
> > >>    printf(1, "%x", -1)
> > >> will show '-1' or '-#1' instead of 'FFFFFFFF'?
> > >
> > > Euphoria's %x format for printf() uses C's %x format,
> > > and only works for numbers up to 32-bits in size.
> > > }}}
<eucode>
> > >      printf(1, "%x", #FFFFFFFF)
> > > </eucode>
{{{

> > > displays FFFFFFFF
> > > as does:
> > > }}}
<eucode>
> > >      printf(1, "%x", -1)
> > > </eucode>
{{{

> > > but Euphoria does *not* consider #FFFFFFFF to be equal to -1.
> >
> > Either it should do so, or
> > }}}
<eucode>
> >    printf(1, "%x", -1)
> > </eucode>
{{{

> > should *not* display FFFFFFFF!!
> > This is a great inconsistency, and a source for confusion (as Derek
> > wrote, too) and bugs.
> >
> > > When people are printing numbers with %x format
> > > they usually want to see -1 displayed as FFFFFFFF,
> >
> > It depends. E.g. people who are new to programming probably would not
> > expect anything, because it will be the first time they deal with hex
> > numbers, and they just learn what they see.
>
>
> I'll interject just here because we probably should understand the
> purpose of %x. My understanding is it is used to display the bit pattern
> of the integer, as it is represented in RAM. And thus -1 should be
> output as FFFFFFFF because that is how -1 is represented as a 32-bit
> value.
>
> I agree it is confusing if you don't know that's what %x is trying to
> do.
>
> > I agree that more experienced programmers, printing numbers with %x
> > format, probably want to see -1 displayed as FFFFFFFF. But this people
> > probably also want Euphoria to consider #FFFFFFFF to be equal to -1!
>
> The difference between #FFFFFFFF and the output of %x is that the first
> is a literal coded into the source code, and such literals are always
> positive integers. And the second is bit pattern display of the integer
> in RAM.
>
> If you want to use negative hexadecimal literals you just place a '-'
> in front of the literal.
>
> atom test
> test = -#1
> test = -#FFFF
>
> If you want to display the value (rather than the bit pattern) of an
> integer in hexadecimal format try this ...
>
> if test < 0 then
>   printf(1, "-%x, ", -test)
> else
>   printf(1, "%x, ", test)
> end if
>
> --
> Derek Parnell
> Melbourne, Australia


Yeah, what Derek said.

    unkmar