Re: Slightly off-topic (was RE: help in getting 7th bit)

I have that t-shirt...

On Thu, 12 Aug 2004 16:22:09 -0400, CWilt@xxxxxxxxxxxx said:
> A computer engineering professor I once had wrote the following on the
> overhead one day:
> 
> There are 10 types of people in the world...
> 
> * Those that know binary
> * Those that don't
> 
> 
> Charles
> 
> 
> > -----Original Message-----
> > From: Scott Klement [mailto:rpg400-l@xxxxxxxxxxxxxxxx]
> > Sent: Thursday, August 12, 2004 4:08 PM
> > To: RPG programming on the AS400 / iSeries
> > Subject: Re: help in getting 7th bit
> > 
> > 
> > 
> > 
> > When you say "7th bit" do you mean the 7th bit from the left 
> > hand side of
> > the byte or the 7th from the right-hand side? Do you start 
> > numbering your
> > bits with 0?  or do you start numbering them from 1?
> > 
> > In other words, if you have a byte with a value of "10000000," which
> > bit is set?  Is it number 0, 1, 7 or 8?
> > 
> > Once you've decided which bit you want to check, create a mask (like
> > "01000000" , where each bit you want ot check is 1, and each 
> > bit you don't
> > care about is 0) convert the binary number to hex, and use 
> > the %bitand()
> > BIF to check it.
> > 
> > For example:
> > 
> >       /free
> > 
> >            // The binary number 01000000 is hex x'40'
> > 
> >            if (%bitand(YSTAT1: x'40') <> x'00');
> >                dsply ('7th bit from the right is set');
> >            endif;
> > 
> >            // The binary number 00000010 is hex x'02'
> > 
> >            if (%bitand(YSTAT1: x'02') <> x'00');
> >                dsply ('7th bit from the left is set');
> >            endif;
> > 
> >       /end-free
> > 
> > 
> > If you're running a release older than V5R2, you can 
> > accomplish the same
> > thing with the TESTB op-code:
> > 
> >       *
> >       *  The binary number 01000000 is hex x'40'
> >       *
> >       * 
> > N01Factor1+++++++Opcode&ExtFactor2+++++++Result++++++++Len++D+HiLoEq
> >      c                   testb     x'40'         YSTAT1       
> >             99
> >      c                   if        *in99 = *on
> >      c                   eval      msg = '7th bit from the 
> > right is on'
> >      c     msg           dsply
> >      c                   endif
> > 
> >       *
> >       *  The binary number 01000000 is hex x'02'
> >       *
> >       * 
> > N01Factor1+++++++Opcode&ExtFactor2+++++++Result++++++++Len++D+HiLoEq
> >      c                   testb     x'02'         YSTAT1       
> >             99
> >      c                   if        *in99 = *on
> >      c                   eval      msg = '7th bit from the left is on'
> >      c     msg           dsply
> >      c                   endif
> > 
> > Personally, I like to make it a more obvious WHY I'm checking 
> > this bit.
> > For that type of thing, I define a named constant that 
> > corresponds to the
> > bit I'm checking.  For example, if bit 7 is determined to be 
> > 01000000 and
> > I'm checking it because it's turned on when an account has 
> > been paid in
> > full, I'd define a constant like this:
> > 
> >      D PaidInFull      c                   x'40'
> > 
> > And then I'd do my test like this:
> > 
> >            if (%bitand(YSTAT1: PaidInFull) <> x'00');
> > 
> > or in older RPG programs:
> > 
> >       * 
> > N01Factor1+++++++Opcode&ExtFactor2+++++++Result++++++++Len++D+HiLoEq
> >      c                   testb     PaidInFull    YSTAT1       
> >             99
> > 
> > I usually bit all of these "bit flags" in a /copy member so that I can
> > reuse them in every program that might need to check the 
> > status of a bit
> > without needing to redefine them everywhere.
> > 
> > 
> > --
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> > 
> --
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