Is there a way to convert an integer to 1 if it is >= 1 without using any relational operator?
boolean, c, logical-operators, math, simd
Solution
#define INT_BITS (CHAR_BIT * sizeof(int))
int make_zero_or_one(int x) {
return 1 - (((x-1) >> (INT_BITS-1)) & 1);
}
Like the other answers, this relies upon the MSB being the sign bit in ints. The function returns 0 for all ints <= 0 and 1 otherwise. The function will fail if `x-1` overflows.
This implementation has no branches in compiled code.
Problem
In my program, I have a statement like the following, inside a loop. ``` y = (x >= 1)? 0:1; ``` However, I want to avoid using any relational operator, because I want to use SIMD instructions, and am not sure if relational operators work well with SIMD. I want something like the following. ``` a = some_operation(x) // a will be either 1 or 0 y = 1 - a ``` Where `some_operation` would convert any number equal or greater than 1 to 1, and keep 0 to 0. So, my question is, is there any `some_operation` that would achieve my purpose?