I'm working on a bitwise problem where I can't use loops or logical operators. I need to return 1 ix x<y else return 0. The valid operators that I can use are ! ~ & ^ | + << >> My code that isn't working so far is: /* isLess - if x < y then return 1, else return 0 * Example: isLess(4,5) = 1. * Legal ops: ! ~ & ^ | + << >> * Max ops: 24 */ int isLess(int x, int y) { return ((x + (~y + 1)) >> 31 ) ; } It seems to have problems with the negative numbers. Going insane!

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Wow, I miss the C++ forums for some weeks, and see the changes! Alright, let's see.
By ops you mean operations as in statement; not uops right? (assembly stuff) 'Cause otherwise it's crazy. I'm assuming you're talking about 2's complement negatives from your code . It seems your problem is that your code does NOT account for negative numbers. Example:

int x = 4; int y = -5

return ((x + (~y + 1)) >> 31 ) ;
/*Dev-C++ defines int in the range of -32768 to +32767, therefore : */

-> return ((4 + (~5 + 1)) >> 31;
-> return (4 + -5) >> 31;
-> return -1 >> 31;
-> return 1;

so 4 is less than -5 that's ok, I do the same thing at times. I'll get the answer to you when I think of it.

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I am new to this forum. I was hanging around this c,c++ section for a while and found this question pretty interesting.
i have a code sample which i feel can do what is expected.bugs and comments are welcome

int fun1(int num1 ,int num2)
{
int temp1 ,temp2;
//if(num1 < num2)
//return 1
//else
//return 0
if(num1 >> 31)
{
if(!(num2 >> 31))
return 1;
temp1 = ~(num1 + 0xFFFFFF);
temp2 = ~(num2 + 0xFFFFFF);
if((~temp2) & temp1)
return 1;
else
return 0;
}
if((~num1) & num2)
return 1;
else
return 0;

}


hope this code work for all possible values

bye
ssv

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Hello ssv, I tested your sample on Dev-C++ (since I was too lazy to study it) using a range of 0 to 512 and using x and x-1 as parameters of your function.

Here's what it returned:
num1 num2 fun1()
0 -1 1 //ok, good so far
1 0 0 //
2 1 1
3 2 0
4 3 1
5 4 0
6 5 1 //ok, I get the picture now...

ad 512... hmm... seems like a odd/even test. Sorry. It looks like you went great depths trying this one. Good try though. By the way, I haven't found a solution myself.

Remember, kvarnerexpress stated that we can't use logical operators, so the if's and else's have to go if you want to declare it a solution.

Here's my test code:

 

 

 

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