Macro-Based Register Config Helper

Code

//
// Created by James Gallegos on 9/23/25.
//
 /*
In embedded systems, registers are often configured by setting specific bits.
To make the code cleaner and reusable, firmware developers use macros to set
fields in a register.

You are given a 16-bit control register layout:

Field	Bits	Position (LSB-first)
ENABLE	1	    Bit 0
MODE	2	    Bits 1–2
SPEED	3	    Bits 3–5
RESERVED	2	Bits 6–7 (must be 0)


Your task is to:

Write macros to:

Set the ENABLE bit
Set the MODE field
Set the SPEED field
Read ENABLE, MODE, SPEED from input
Use the macros to pack a final 16-bit register value
RESERVED bits (6–7) must be left 0
  */

// #define NAME(param1, param2, ..., paramN)   expression_using_them

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

#define ENABLE_POS  0
#define MODE_POS    1
#define SPEED_POS   3

#define ENABLE_MASK (0x1u << ENABLE_POS)
#define MODE_MASK   (0x3u << MODE_POS)
#define SPEED_MASK  (0x7u << SPEED_POS)

// Packs are basically  formulas condensed into a single variable
#define PACK_ENABLE(en) ( (uint16_t)(((en) & 0x1u) << ENABLE_POS) )
#define PACK_MODE(md)   ( (uint16_t)(((md) & 0x3u) << MODE_POS) )
#define PACK_SPEED(sp)  ( (uint16_t)(((sp) & 0x7u) << SPEED_POS) )

uint16_t build_register(uint8_t enable, uint8_t mode, uint8_t speed) {
    uint16_t reg = 0;                    // start with all bits 0 (incl. RESERVED)
    reg |= PACK_ENABLE(enable);          // bit 0
    reg |= PACK_MODE(mode);              // bits 1–2
    reg |= PACK_SPEED(speed);            // bits 3–5
    // Bits 6–7 are RESERVED and left 0 by construction
    return reg;
}

int main() {
    uint8_t enable, mode, speed;
    scanf("%hhu %hhu %hhu", &enable, &mode, &speed);

    uint16_t reg = build_register(enable, mode, speed);
    printf("%u", reg);
    return 0;
}

Solving Approach