Keep Only the Highest Set Bit

Code

#include <stdio.h>
#include <stdint.h>

// Complete the function
uint16_t highest_set_bit(uint16_t reg) {
    if (reg == 0) return 0;

    int watermark = 0;
    for (int i = 0; i < 16; i++) {
        if (reg & (1 << i)) {
            watermark = i;
        }
    }
    return (1 << watermark);
}

int main() {
    uint16_t reg;
    scanf("%hu", &reg);

    uint16_t result = highest_set_bit(reg);
    printf("%hu", result);
    return 0;
}

Solving Approach

1. Lets get the 0 case out of the way first, if the register is 0, then there will be no highest set bit, return 0.

2. To check if a value is set we AND with 1, In a loop of 16 to check each bit, store the index of the highest set bit and return 1 left shifted to that index.