Subj : Re: possible overflow?
To   : comp.programming
From : Rob Somers
Date : Thu Aug 25 2005 10:07 pm

Peter Shaggy Haywood wrote:
> 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.)
> 

Ah, thank you all for your input - I will study it this weekend, and if 
I have any questions, I will post back.  My apologies also for the 
double post - my service provider was not giving me decent news service 
on the weekend, and I mistakenly posted twice.

Rob Somers

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