This is a classic interview question: You are asked to write a function that returns a bigger number of both, without using any comparison operator, such as if, or ternary operator (e.g. ?).
1 2 3 | int max(int a, int b) { // TODO } |
int max(int a, int b) {
// TODO
}This is to return (a > b ? a : b); If a is larger than b returns a otherwise b. We let 
, thus if c is negative, the function returns b otherwise a.
if k = 0 and c is non-negative.
if k = 1 and c is negative.
So, the target is to compute the value of k, which is the MSB (most significant bit, the signed bit) of the integer c, negative means a smaller than b.
Thus, we have the following solution (bit right shift 31 positions and we have the signed bit at the right-most bit, the least significant bit (LSB)) :
1 2 3 4 5 6 | inline int max(int a, int b) { int c = a - b; int k = (c >> 31) & 1; return (a - k * c); } |
inline int
max(int a, int b) {
int c = a - b;
int k = (c >> 31) & 1;
return (a - k * c);
}–EOF (The Ultimate Computing & Technology Blog) —
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