Subj : Re: possible overflow?
To   : comp.programming
From : Shaggy
Date : Fri Aug 26 2005 01:19 am

Groovy hepcat mr_semantics@hotmail.com was jivin' on 21 Aug 2005
05:08:49 -0700 in comp.programming.
possible overflow?'s a cool scene! Dig it!

>I am still fiddling with bitwise operations - this time I have been
>working
>on a program that accepts input (an unsigned integral) from the user,
>and
>then after some 'conversion' outputs that number in binary format.  I
>have
>one problem that is vexing me though:
>
>#include <stdio.h>

#include <limits.h>

>int main(void)
>{
>        unsigned int input = 8;
>        unsigned long int i;
>        unsigned long int j = 0;

        size_t number_of_bits = sizeof j * CHAR_BIT;

        j = (1UL << (number_of_bits - 1));
>        for (i = 1; i != 0; i <<= 1) {
>                if (input & j) {
>                       (void) putchar('1');
>                } else {
>                       (void) putchar('0');
>                }
>                j >>= 1;
>        }
>        puts("");
>        return 0;
>}

  I must say that your code goes to unnecessary lengths to do simple
things. There's no need for so much complexity. As someone else
already pointed out, you can replace the shifting of i with a simple
count.
  Also, it's best to avoid "magic numbers" in code, especially when
they introduce an implementation dependance. The number of bits in a
byte is not universally 8. The standard C macro CHAR_BIT, defined in
limits.h, returns the (implementation defined) number of bits in a
byte.
  You must also realise that there may be non-value bits, even trap
bits, in any integral type other than the character types. This makes
your code inherently non-portable. But if you can live with excluding
those implementations that have non-value bits in their integral
types, then that's OK. (Yes, I am being quite anal here. It's for a
reason: to teach you better programming habbits. Correctness and
portability are key.)

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