Counting bits

[rishab@dxm.ernet.in]

"Timothy L. Nali" <tn0s+@andrew.cmu.edu>:
> > Eli Brandt@jarthur.cs.hm 
> > int byte_ones(int a)
> > // hope this is correct...
> > {
> >         a = (a & 0x55) + (a & 0xAA)/2;          // 0x55 == 01010101b
> [...]
> Note that some compilers might not be smart enough to use logical shift
> ops and instead use expensive division ops.  Just to be safe...
> 
> int byte_ones(int a)
>          a = (a & 0x55) + ((a & 0xAA) << 1);          // 0x55 == 01010101b
                                    ^^^^^^^^^
Let me guess: you're one of the lucky users of the RBO (Reverse Bit Order)
SuperDecryptor from the NSA, where the LSB is the one at the extreme left?

Or did you mean ((a & 0xAA) >> 1)   ;)

My personal preference for byte operands is unsigned char - this ensures
that right shifts are not sign-extended by the most brain dead compiler, and
might use only one byte for the parameter.

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