69. Extract Bit Field from 16-bit Register

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

uint8_t extract_field(uint16_t reg) {
    return (reg >> 4) & 0x1F;  // Shift right to align bits 4–8 to LSB, mask 5 bits
}

int main() {
    uint16_t reg;
    scanf("%hx", &reg);  // Hexadecimal input
    printf("%u", extract_field(reg));
    return 0;
}

Why is this useful in firmware?

Registers often store multiple fields like:

• Bits 0–2: mode
• Bits 4–8: prescaler
• Bits 10–15: status code

You must extract such fields without modifying the rest.

Solution Logic

• Shift right by 4 so that bit 4 becomes bit 0
• Use & 0x1F to mask the 5 least significant bits (bit 0–4)