My solution just tests bit i and either sets or clears bit j based on
the result. Then it does the same testing bit j and setting or
clearing bit i.
There are many other possibilities. It would be slick if C shift
operators accepted negative shift values. But they don't. Instead you
could shift the bits down to position 0 then shift them back up to
their swapped positions and substitute in the input value. This one
has a spooky symmetry.
unsigned swap(unsigned x, int i, int j)
{
unsigned bit_i = (1u << i) & x;
unsigned bit_j = (1u << j) & x;
return (x ^ bit_i ^ bit_j) | (bit_i >> i << j) | (bit_j >> j << i);
}
On Sep 13, 9:07 pm, Dave <[email protected]> wrote:
> Replying to myself: I should proofread better _before_ I post. Sorry,
> but the explanation should say
>
> ni is bit i of n. nj is bit j of n. n & ~(ni | nj) removes the two
> bits, and then they are shifted to the exchanged positions and or'd
> in.
>
> Dave
>
> On Sep 13, 2:04 pm, Dave <[email protected]> wrote:
>
>
>
> > @Kumar: How about this:
>
> > int exchange2bits(int n, int i, int j) // exchange bits i and j of n.
> > {
> > int ni, nj;
> > ni = n & (1 << i);
> > nj = n & (1 << j);
> > return n & ~(ni | nj) | ((ni >> i) << j) | ((nj >> j) << i);
>
> > }
>
> > ni is bit i of n. nj is bit j of n. n & (ni | nj) removes the two
> > bits, and then they are shifted to the exchanged positions and or'd
> > in.
>
> > Dave
>
> > On Sep 13, 1:50 pm, kumar raja <[email protected]> wrote:
>
> > > Suppose a number 'n' is given and two bits positions i,j present in
> > > binary
> > > representation of n .
>
> > > Then how to exchange the contents of the two bits i and j.
>
> > > E.g. n= 13
> > > its binary representation is 0000 1101 (just for now consider 8 bit
> > > number)
>
> > > i= 2,j=6
>
> > > o/p : 0100 1001 = 73
>
> > > please suggest some effective way to do this...
>
> > > --
> > > Regards
> > > Kumar Raja
> > > M.Tech(SIT)
> > > IIT Kharagpur,
> > > [email protected]
> > > 7797137043.
> > > 09491690115.- Hide quoted text -
>
> > - Show quoted text -- Hide quoted text -
>
> - Show quoted text -
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