Finding MSB in bit string

[Michael Tiemann]

In article <7143 at boring.mcvax.UUCP>, guido at mcvax.uucp (Guido van Rossum) writes:
> >What's a good general method?  How would a real programmer do it?
> 
> This has been discussed in this group a while ago.  It goes something like
> 
> 	return count[x&0xff] + count[(x>>8)&0xff] +
> 		count[(x>>16)&0xff] + count[(x>>32)&0xff;
						^^
						24
> 
> (I hope this time I didn't forget some offsets like in my solution of
> the MSB problem.)

Nope, just some arithmetic.

How about

	cnt = count[x&0xff];
	cnt += count[(x>>=8) & 0xff];
	cnt += count[(x>>=8) & 0xff];
	return	cnt + count[x&0xff];

for those poor souls without barrel shifters.

But this is not a *general* method, since there is no parameterization
of the bit-string (!). Not all bit-strings are 32-bit ints. I won't
*even* touch the issue of bit-string alignment...

Michael
tiemann at mcc.com