Message-ID: <3F24AA4B.589D3482@worldnet.att.net>
From: Paul Cousoulis <paulcsouls AT worldnet DOT att DOT net>
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Subject: Re: integer overflow
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Date: Mon, 28 Jul 2003 04:45:34 GMT
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To: djgpp AT delorie DOT com
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1LU ? I guess the LU means Long Unsigned. Is that now part of standard
C? I would of guessed the preprocessor would have handled the math first
and the storage later.

Thanks
Paul

Martin Ambuhl wrote:
> 
> Paul Cousoulis wrote:
> > Why does this code result in an integer overflow?
> >
> > unsigned long res;
> >
> > res = (1<<31)-1;
> 
> Because (1 << 31) is a signed expression. Never use signed integers for
> bit twiddling. Here's an example without such overflow.
> 
> #include <stdio.h>
> 
> int main(void)
> {
>      unsigned long res;
>      res = 1LU << 31;
>      printf("1LU << 31     : %lu\n", res);
>      res = (1LU << 31)-1;
>      printf("(1LU << 31)-1 : %lu\n", res);
>      return 0;
> }
> 
> 1LU << 31     : 2147483648
> (1LU << 31)-1 : 2147483647