20. Clear Specific Bits in a 32-bit Register

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

uint32_t clear_bits(uint32_t reg, uint8_t pos, uint8_t len) {
    if (len == 0 || pos >= 32) return reg;    // invalid case
    if (len > 32 - pos) len = 32 - pos;       // clamp length

    uint32_t mask = ((1u << len) - 1) << pos; // range mask
    reg &= ~mask;                             // clear bits
    return reg;
}

int main() {
    uint32_t reg;
    uint8_t pos, len;
    scanf("%u %hhu %hhu", &reg, &pos, &len);
    printf("%u", clear_bits(reg, pos, len));
    return 0;
}