Extract and Modify Field in a 32-bit Register

Code

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

uint32_t update_register(uint32_t reg) {
    uint32_t fields = (reg >> 10) & 0x1F; //bits from 0 to 4
    reg &= ~(0x1F << 10); //clear bits 10 to 14
    uint32_t mask = 1UL;
    if(fields<31){
        while(fields & mask){ //detection du 0 pour utilisation mask
            fields ^= mask;
            mask <<= 1;
        }
        fields ^= mask;
    }
    reg |= (fields << 10);
    return reg;
    
}

int main() {
    uint32_t reg;
    scanf("%u", &reg);
    uint32_t updated = update_register(reg);
    printf("%u", updated);
    return 0;
}

Solving Approach