Comments on: Saving an Operation or 20 http://thesnarky.com/2007/01/31/saving-an-operation-or-20/ The Words of the One Who Calls Himself a Philosopher Tue, 26 Oct 2010 22:13:34 +0000 hourly 1 http://wordpress.org/?v=3.3.1 By: Adam Helps http://thesnarky.com/2007/01/31/saving-an-operation-or-20/comment-page-1/#comment-4162 Adam Helps Wed, 31 Jan 2007 21:08:04 +0000 http://thesnarky.com/archives/128#comment-4162 Snarky made explicit casting illegal too, but assigning an int to an unsigned is an implicit cast, so I think I'm OK... int logical_not( int x ) { unsigned y = x; y = (y >> 1) | (y & 1); y = y + ~0; return y >> 31; } The basic idea is to create some value that is positive (and greater than zero) if any bits are set and zero if no bits are set; I then subtract 1 from that value. If the result is negative, I had a 0; if the result is positive, I had a non-zero. Snarky made explicit casting illegal too, but assigning an int to an unsigned is an implicit cast, so I think I’m OK…

int logical_not( int x )
{
unsigned y = x;
y = (y >> 1) | (y & 1);
y = y + ~0;
return y >> 31;
}

The basic idea is to create some value that is positive (and greater than zero) if any bits are set and zero if no bits are set; I then subtract 1 from that value. If the result is negative, I had a 0; if the result is positive, I had a non-zero.

]]> By: Snarky http://thesnarky.com/2007/01/31/saving-an-operation-or-20/comment-page-1/#comment-4160 Snarky Wed, 31 Jan 2007 18:00:31 +0000 http://thesnarky.com/archives/128#comment-4160 Bah, yea, additional rules left unstated. Return 0 for false, 1 for true. And you can only use: ~ >> << & | + ^ I realized last night going to bed this answer would pop up, so.... there's the extra rules to actually make it *hard*. Bah, yea, additional rules left unstated.

Return 0 for false, 1 for true. And you can only use:
~
>>
<<
&
|
+
^

I realized last night going to bed this answer would pop up, so…. there’s the extra rules to actually make it *hard*.

]]> By: Anonymous http://thesnarky.com/2007/01/31/saving-an-operation-or-20/comment-page-1/#comment-4159 Anonymous Wed, 31 Jan 2007 16:40:43 +0000 http://thesnarky.com/archives/128#comment-4159 int logical_not( int x ) { return x && 1; } int logical_not( int x ) {
return x && 1;
}

]]> By: Peter Harkins http://thesnarky.com/2007/01/31/saving-an-operation-or-20/comment-page-1/#comment-4158 Peter Harkins Wed, 31 Jan 2007 15:21:55 +0000 http://thesnarky.com/archives/128#comment-4158 One operation, I guess: int logical_not(int x) { return !x; } It has no tests or control structures, but as you and your friend both broke it down so far I'm guessing there was an additional rule you've left unstated? One operation, I guess:

int logical_not(int x) {
return !x;
}

It has no tests or control structures, but as you and your friend both broke it down so far I’m guessing there was an additional rule you’ve left unstated?

]]>