Convert two's complement to sign-magnitude

Question

I need to convert from two\'s complement to sign-magnitude in C using only the operators

! ~ & ^ | + << >>

My approach is t

Answer 1

I'm not entirely sure what the output should be, but to obtain the magnitude you can do something like this:

int m = (a^(a>>31)) + sign;

Basically, shifting a negative number 31 bits to the right will make it all 1's, or 0xffffffff, which you can then use to xor the input number and make it positive. As you correctly noted sign needs to be added then for the correct result in that case.

If the input number was positive to begin with, the shift results in a zero and so the xor does nothing. Adding sign in that case also doesn't do anything, so it results in the input number.