Re: [Dev-C++] Shift operators portability

[Per W. <pw...@ia...>]

They don't wrap around since they are shift operators and not rotate
operators.

Some care should be used with negative numbers since most machines are
using two-complement numbers which high bit specifies if number is
negative. By shifting that bit, you definitely don't get mult/div with
two.

As long as you don't try to load only a part of a number and perform a
shift on, big or little endian doesn't matter. The endianness is only how
the number is stored in memory. When loaded into the processor, it is just
a number.

Big or little endian doesn't matter - unless a number is processed
The sample program below doesn't work becase it isn't assigning the result
of the shifts.

count <<= 1;
count >>= 1;

or

count = count << 1;
count = count >> 1;

/Per W


On Mon, 22 Sep 2003, Michael D. Smith wrote:

>
> No wraparound, they drop off the end, at least on any machine I've ever
> been familiar with.
>
> I thought I would try, see how it works on this machine and got nothing. No
> compiler error, and no change in the int.
>
> Anyone know why this produces nothing (16) every time? And I tried other
> numbers, in both positions, as well. Even tried turning it around -- Same
> thing, nothing, every time. It seems there should be some effect, or an
> error..
>
> I have an AMD processor and no idea if it's big or little endian.
>
>
>
> #include<iostream.h>
> #include<stdlib.h>
> #include<fstream.h>
>
>    int main()
>    {
>       int count = 16;
>
>       count >> 2;
>         cout << "count = " << count << "\n";
>
>       2 << count;
>         cout << "count = " << count << "\n";
>
>       system ("pause");
>       return 0;
>    }
>
>
> At 08:14 PM 9/22/03, you wrote:
> >Hi there.
> >
> >Are the shift operators ( << and >> ) portable?
> >i.e.
> >Does x << 1 have the same effect as multiplying by 2 ?
> >and
> >Does x >> 1 have the same effect as dividing by 2?
> >On both big and little endian order machines?
> >
> >also is there any wraparound?
> >i.e. in a shift the bits that are pushed out of the data structure placed
> >at the back-end of the data structure (on the other side of where they
> >were pushed out)?
> >
> >Thanks in Advance
> >David McKen
> >
> >
> >Do you Yahoo!?
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