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Hi

I need to copy bits 0-6 from a byte into bits 0-6 of a word. then i need to
copy bits 0-6 from another byte into bits 7-14 of this word.

I am going gray from messing around with AND, OR, >> and << operators. I
hope the collective audience of this group can point out an obvious solution
to this problem so that i can kick myself for not seeing the obvious.

The main problem i am experiencing is preserving the LO byte of the word
when copying from the 2nd byte.

Thanks.

curium wrote in news:3f45ae9d$0$11384$ :

> Hi
>
> I need to copy bits 0-6 from a byte into bits 0-6 of a word. then i
> need to copy bits 0-6 from another byte into bits 7-14 of this word.
>
> I am going gray from messing around with AND, OR, >> and << operators.
> I hope the collective audience of this group can point out an obvious
> solution to this problem so that i can kick myself for not seeing the
> obvious.
>
> The main problem i am experiencing is preserving the LO byte of the
> word when copying from the 2nd byte.
>

unsigned merge( unsigned char lo, unsigned char hi )
{
unsigned result = static_cast< unsigned >(lo) & 0x3F;

result |= ( static_cast< unsigned >(hi) & 0x3F ) << 6;

return rsult;
}


HTH

Rob.
--
http://www.victim-prime.dsl.pipex.com/

Rob Williscroft wrote:
> curium wrote:
>
> > I need to copy bits 0-6 from a byte into bits 0-6 of a word. then i
> > need to copy bits 0-6 from another byte into bits 7-14 of this word.
> >
> > I am going gray from messing around with AND, OR, >> and <<
> > operators. I hope the collective audience of this group can point
> > out an obvious solution to this problem so that i can kick myself
> > for not seeing the obvious.
> >
> > The main problem i am experiencing is preserving the LO byte of
> > the word when copying from the 2nd byte.
> >
>
> unsigned merge( unsigned char lo, unsigned char hi )
> {
> unsigned result = static_cast< unsigned >(lo) & 0x3F;
>
> result |= ( static_cast< unsigned >(hi) & 0x3F ) << 6;
>
> return rsult;
> }

Because some idiot cross posted to c.l.c and c.l.c++, you have
posted something that is not applicable on c.l.c. So lets change
the function body to be valid C, and hope it is still valid C++


unsigned int result;

result = ((hi & 0x3f) << 6) | (lo & 0x3f);
return result;

These values can never cause an integer overflow. There is no
such thing as an AND or an OR operator.

--
Chuck F () ()
Available for consulting/temporary embedded and systems.
<http://cbfalconer.home.att.net> USE worldnet address!

> I don't understand what you mean by
> "There is no such thing as an AND or an OR operator."

AND and OR and not defined as keywords in C.

You'd use one of:
&
&&
|
||

Nudge wrote:
>
> > I don't understand what you mean by
> > "There is no such thing as an AND or an OR operator."
>
> AND and OR and not defined as keywords in C.

I can understand that well enough to say that
that makes no sense at all.
There's a lot more to C, than just keywords.

> You'd use one of:
> &
N868
6.5.10 Bitwise AND operator

> &&
N869
6.5.13 Logical AND operator

> |
N868
6.5.12 Bitwise OR operator


> ||
N869
6.5.14 Logical OR operator

--
pete

Rob Williscroft <> wrote in message news:<Xns93DF48389C834ukcoREMOVEfreenetrtw@195.129 .110.201>...
> curium wrote in news:3f45ae9d$0$11384$ :
>
> > I need to copy bits 0-6 from a byte into bits 0-6 of a word. then i
> > need to copy bits 0-6 from another byte into bits 7-14 of this word.
> >
> > I am going gray from messing around with AND, OR, >> and << operators.
> > I hope the collective audience of this group can point out an obvious
> > solution to this problem so that i can kick myself for not seeing the
> > obvious.
>
> unsigned merge( unsigned char lo, unsigned char hi )
> {
> unsigned result = static_cast< unsigned >(lo) & 0x3F;
>
> result |= ( static_cast< unsigned >(hi) & 0x3F ) << 6;
>
> return result;
> }

Or if I understood the problem description, this:

unsigned merge( unsigned result, unsigned char lo, unsigned char hi )
{
result &= ~( (1<<14) - 1 );

result |= lo & 0x3F;

result |= ( hi & 0x3F ) << 6;

return result;
}

The casts are not needed.

Sam

Rob Williscroft <> wrote in message news:<Xns93DF48389C834ukcoREMOVEfreenetrtw@195.129 .110.201>...
> curium wrote in news:3f45ae9d$0$11384$ :
>
> > I need to copy bits 0-6 from a byte into bits 0-6 of a word. then i
> > need to copy bits 0-6 from another byte into bits 7-14 of this word.
> >
> > I am going gray from messing around with AND, OR, >> and << operators.
> > I hope the collective audience of this group can point out an obvious
> > solution to this problem so that i can kick myself for not seeing the
> > obvious.
>
> unsigned merge( unsigned char lo, unsigned char hi )
> {
> unsigned result = static_cast< unsigned >(lo) & 0x3F;
>
> result |= ( static_cast< unsigned >(hi) & 0x3F ) << 6;
>
> return rsult;
> }

Or if I understood the problem description, this:

unsigned merge( unsigned result, unsigned char lo, unsigned char hi )
{
result &= ~( (1<<14) - 1);

result |= lo & 0x7F;

result |= ( hi & 0x7F ) << 7;

return result;
}

The casts are not needed.

Sam

P.S. Ignore my other reply.

pete wrote:
> CBFalconer wrote:
> > Rob Williscroft wrote:
> > > curium wrote:
> > >
> > > > I need to copy bits 0-6 from a byte into bits 0-6 of a word.
> > > > then i need to copy bits 0-6 from another byte
> > > > into bits 7-14 of this word.
> > > >
> > > > I am going gray from messing around with AND, OR, >> and <<
> > > > operators. I hope the collective audience of this group can
> > > > point out an obvious solution to this problem so that i can
> > > > kick myself for not seeing the obvious.
> > > >
> > > > The main problem i am experiencing is preserving the LO byte
> > > > of the word when copying from the 2nd byte.
> > >
> > > unsigned merge( unsigned char lo, unsigned char hi )
> > > {
> > > unsigned result = static_cast< unsigned >(lo) & 0x3F;
> > >
> > > result |= ( static_cast< unsigned >(hi) & 0x3F ) << 6;
> > > return rsult;
> > > }
> >
> > Because some idiot cross posted to c.l.c and c.l.c++, you have
> > posted something that is not applicable on c.l.c. So lets change
> > the function body to be valid C, and hope it is still valid C++
> >
> >
> > unsigned int result;
> >
> > result = ((hi & 0x3f) << 6) | (lo & 0x3f);
> > return result;
> >
> > These values can never cause an integer overflow. There is no
> > such thing as an AND or an OR operator.
>
> I don't understand what you mean by
> "There is no such thing as an AND or an OR operator."

The operators are || and &&, unless you #include <iso646.h>, when
the macros 'or' and 'and' expand to those anyway. That also give
the equivalence of 'bit_and' and &, and of 'bit_or' and |.

--
Chuck F () ()
Available for consulting/temporary embedded and systems.
<http://cbfalconer.home.att.net> USE worldnet address!

On Fri, 22 Aug 2003 11:44:48 GMT, pete <> wrote:

>>
>> > I don't understand what you mean by
>> > "There is no such thing as an AND or an OR operator."
>>
>> AND and OR and not defined as keywords in C.
>
>I can understand that well enough to say that
>that makes no sense at all.
>There's a lot more to C, than just keywords.

I think you're confusing operators and operations.

The set of C operators is quite small, and does not include either AND
or OR.

--
Al Balmer
Balmer Consulting

CBFalconer wrote:
>
> pete wrote:
> > CBFalconer wrote:
> > > Rob Williscroft wrote:
> > > > curium wrote:
> > > >
> > > > > I need to copy bits 0-6 from a byte into bits 0-6 of a word.
> > > > > then i need to copy bits 0-6 from another byte
> > > > > into bits 7-14 of this word.
> > > > >
> > > > > I am going gray from messing around with AND, OR, >> and <<
> > > > > operators. I hope the collective audience of this group can
> > > > > point out an obvious solution to this problem so that i can
> > > > > kick myself for not seeing the obvious.
> > > > >
> > > > > The main problem i am experiencing is preserving the LO byte
> > > > > of the word when copying from the 2nd byte.
> > > >
> > > > unsigned merge( unsigned char lo, unsigned char hi )
> > > > {
> > > > unsigned result = static_cast< unsigned >(lo) & 0x3F;
> > > >
> > > > result |= ( static_cast< unsigned >(hi) & 0x3F ) << 6;
> > > > return rsult;
> > > > }
> > >
> > > Because some idiot cross posted to c.l.c and c.l.c++, you have
> > > posted something that is not applicable on c.l.c. So lets change
> > > the function body to be valid C, and hope it is still valid C++
> > >
> > >
> > > unsigned int result;
> > >
> > > result = ((hi & 0x3f) << 6) | (lo & 0x3f);
> > > return result;
> > >
> > > These values can never cause an integer overflow. There is no
> > > such thing as an AND or an OR operator.
> >
> > I don't understand what you mean by
> > "There is no such thing as an AND or an OR operator."
>
> The operators are || and &&,
> unless you #include <iso646.h>, when
> the macros 'or' and 'and' expand to those anyway.

I'm having a very hard time parsing that sentence.

You're saying that when you #include <iso646.h>,
then || and && aren't the operators, but that when you
don't #include <iso646.h>, then they are the operators.

I'm even more confused about what you're saying now.
What do you mean by "The", in "The operators" ?
There's no || or && in the posted code,
so you must mean that those operators have been previously
referred to in the text of this thread.
*Which* operators are || and && ?
The ones which there are no such things as ?

Is your objection that he did not precisely specify
"bitwise AND operator"
and
"bitwise inclusive OR assignment operator"
?

--
pete