48. Validate Configuration Register Layout

#include <stdio.h>

typedef struct {
    unsigned short reg;
} ConfigRegister;

int validate_config(ConfigRegister *cfg) {
    unsigned short value = (*cfg).reg;

    // Check if Enable bit is set (bit 0)
    if ((value & 0x0001) == 0)
        return 0;

    // Extract priority (bits 2–3)
    unsigned short priority = (value >> 2) & 0x03;
    if (priority == 0x03)  // Invalid priority
        return 0;

    // Check reserved bits (bits 4–15) are all 0
    if ((value & 0xFFF0) != 0)
        return 0;

    return 1;
}

int main() {
    ConfigRegister cfg;
    scanf("%hx", &cfg.reg);

    int result = validate_config(&cfg);
    printf("%d", result);

    return 0;
}

Bitfields and config validation are the foundation of hardware-level programming.

Most control registers in firmware map bits to features, and validation is crucial before applying the configuration.

Solution Logic:

• Use bitmask 0x0001 to check the Enable bit
• Shift and mask bits 2–3 to extract priority
• Use 0xFFF0 mask to ensure bits 4–15 are clear
• Combine all checks into one function

Alternate Solution

int validate_config(ConfigRegister *cfg) {
    unsigned short val = cfg->reg;

    int enable = val & 0x0001;
    int priority = (val >> 2) & 0x03;
    int reserved_clear = (val & 0xFFF0) == 0;

    return (enable && priority != 0x03 && reserved_clear);
}