How do I find whether a number is positive, negative or zero without using if or for? [duplicate]

问题

This question already has answers here:

Checking whether a number is positive or negative using bitwise operators (15 answers)

Closed 6 years ago.

I want to implement the sign and zero flag setting in microprocessor. So I need to write a function to find whether the number is positive, negative or zero without using if or for loops and also only Boolean and bitwise operators are allowed. I did the following. But how to I implement it for zero condition ?

int status (int x) {
    int sign = (x >> 31);
    return sign;
}

Any suggestions ?

回答1:

The following will return -1 for negative values, 0 for zero, 1 for positive values of x.

int status (int x) {
  int sign = (x > 0) - (x < 0); 
  return sign;
}

回答2:

Is this enough for your purpose?

int status(int val)
{
    int minus = (val&0x80000000)&&TRUE;
    int pos = (val&0x7FFFFFFF)&&(!(val&0x80000000));
    int r = 0 - minus + pos;
    return r;
}

回答3:

Try this

int status (unsigned no) {
  int sign = 0;

   // If Zero             // If -Ve = -1 OR If +Ve = -2
   (sign = ( no | 0 )) && ( sign = (~( ( (no << 1) >> 1 ) == no)) );

   // If +Ve
   (sign == -2) && (sign = 1);

  return sign;
}

来源：https://stackoverflow.com/questions/16728013/how-do-i-find-whether-a-number-is-positive-negative-or-zero-without-using-if-or