365 Days of Code - Day 064
Project Status
| Project | Language | Status | Due Date | Latest Update |
|---|---|---|---|---|
| Personal Website | Hugo | Ongoing | None | The site is live. Continuous improvements ongoing. |
| Laravel From Scratch | Laravel (PHP) | In-Progress | 2026-03-31 | Episode 8 |
| PRM | Laravel (PHP) | In-Progress | 2026-03-31 | Working alongside other Laravel projects. |
| Client Website (J.L.) | Laravel (PHP) | In-Progress | 2026-03-31 | Working alongside other Laravel projects. |
| Project Euler | C | Ongoing | None | Working on P25. BigInt (AI gen) was a waste of time, need to rewrite |
| Practice Java | Java | Paused | None | Installed, need to find a good project. |
| Practice Python | Python | Paused | None | Installed, need to find a good project. |
| Learn Go | Go | Paused | None | Installed, work on LDAP Injector from ippsec. |
| Learn Rust | Rust | Haven’t Started | None | Installed, will try network protocols after finishing in C and Zig. |
| Learn Elixir | Elixir | Haven’t Started | None | Installed, need a good tutorial project. |
| Learn Haskell | Haskell | Haven’t Started | None | Installed, need a good tutorial project. |
| Learn Zig | Zig | Haven’t Started | None | Installed, will try network protocols after finishing in C. |
| Linux+ | N/A | In-Progress | 2026-03-31 | Reading Chapter 4. |
| Cyber Quest 2026 | N/A | In-Progress | 2026-02-28 | Finished quiz 1 with 75%. |
| Operating Systems | N/A | In-Progress | 2026-03-31 | Reading Chapter 4: Abstraction |
| Grey-Hat Hacking | Various | In-Progress | 2026-03-31 | Reading Chapter 8: Threat Hunting Lab |
| PHP Time Tracker | PHP | Beta Finished | None | Working on a basic level. |
| HTTP Status Code Reader | C | Complete | 2026-02-18 | Complete. |
| ZSH Configuration | bash/zsh | Complete | None | Sort of an ongoing process, but complete for now. Works good. |
| Network Protocols | C | In-Progress | None | Working on V3, implementing IPv6. |
| Discinox Website | HTML, CSS, JS | Complete | 2026-03-04 | The site is live. |
| DiroffTech Website | HTML, CSS, JS | Complete | 2026-03-05 | The site is live. git-lfs needs to be initialized for images. |
| Automate Backups | bash | Complete | 2026-03-08 | Backups done. |
| CodinGame | C | Ongoing | None | Completed GhostLegs, ASCII Art. |
CodinGame - MiniCPU Instruction Decoder
Another day, another CodinGame challenge. This one has us performing a simple CPU emulation, reading in instructions, and manipulating registers.
A simple 8-bit CPU emulator must be debugged. The CPU has 4 registers (
R0,R1,R2,R3) initialized to0.
- Instructions are encoded as hexadecimal bytes:
| Ins. | Reg. | Reg. or Val. | Description |
|---|---|---|---|
| 01 | X | V | Load value V into register RX |
| 02 | X | Y | Add register RY to register RX |
| 03 | X | Y | Subtract register RY from register RX |
| 04 | X | Y | Multiply register RX by register RY |
| 05 | X | Increment register RX by 1 | |
| 06 | X | Decrement register RX by 1 | |
| FF | Halt execution |
- Where
XandYare register indices (0-3), andVis an immediate byte value. - All arithmetic wraps at 256 (8-bit unsigned). Overflow wraps to 0, underflow wraps to 255.
- The first instruction is not guaranteed to be 01 (MOV). Programs may start with any instruction, including 05 (INC) or 06 (DEC).
- The smallest valid program is just FF (HLT).
- Execute the program and output the final register values.
Input
- Line 1: A string of space-separated hexadecimal bytes program
Output
- 4 lines: The decimal value of each register R0, R1, R2, R3, one value per line
Constraints
- Program length ≤ 100 bytes
- For the opcodes 02, 03 and 04, X ≠ Y
- Program always ends with HLT (FF) as an opcode. Byte value FF may also appear as an immediate value V.
Example Input:
plaintext
01 00 0A 01 01 05 02 00 01 03 00 01 FF
| |
Example Output:
plaintext
10 5 0 0
| |
Initial Thoughts
This looks pretty simple on the surface. Store the state of the registers, create functions for each of the operations, and output the final state.
Code
I was able to essentially one-shot this code. It required some debugging to ensure I got the reads correct, but the problem was fairly easy overall. I will note that I had to fill out the entire switch statement for the program to operate as expected. In my naivite, I only created the first opcode, mov in the switch and started testing. Since I wasn’t consuming the other opcodes, I was getting garbage output and seg faults.
c
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <stdbool.h>
#include <stddef.h>
#include <stdint.h>
/**
* Decode and execute the MiniCPU bytecode program.
**/
void mov(uint8_t *r, uint8_t val)
{
*r = val;
return;
}
void add(uint8_t *r1, uint8_t *r2)
{
*r1 += *r2;
return;
}
void sub(uint8_t *r1, uint8_t *r2)
{
*r1 -= *r2;
return;
}
void mul(uint8_t *r1, uint8_t *r2)
{
*r1 *= *r2;
return;
}
void inc(uint8_t *r)
{
*r += 1;
return;
}
void dec(uint8_t *r)
{
*r -= 1;
return;
}
int main()
{
// Space-separated hex bytes representing CPU instructions
char program[501] = "";
scanf("%[^\n]", program);
uint8_t R0 = 0;
uint8_t R1 = 0;
uint8_t R2 = 0;
uint8_t R3 = 0;
uint8_t *arr[4] = {&R0, &R1, &R2, &R3};
int pos = 0;
int consumed;
unsigned int byte;
bool halted = false;
while (!halted && sscanf(program + pos, "%x%n", &byte, &consumed) == 1) {
uint8_t b = (uint8_t)byte;
pos += consumed;
fprintf(stderr, "%x\n", b);
switch (b)
{
case 0x01:
{
fprintf(stderr, "mov\n");
sscanf(program + pos, "%x%n", &byte, &consumed);
uint8_t r = (uint8_t)byte;
fprintf(stderr, "r: %d\n", r);
pos += consumed;
sscanf(program + pos, "%x%n", &byte, &consumed);
uint8_t val = (uint8_t)byte;
fprintf(stderr, "val: %d\n", val);
pos += consumed;
mov(arr[r], val);
break;
}
case 0x02:
{
fprintf(stderr, "add\n");
sscanf(program + pos, "%x%n", &byte, &consumed);
uint8_t r1 = (uint8_t)byte;
fprintf(stderr, "r1: %d\n", r1);
pos += consumed;
sscanf(program + pos, "%x%n", &byte, &consumed);
uint8_t r2 = (uint8_t)byte;
fprintf(stderr, "r2: %d\n", r2);
pos += consumed;
add(arr[r1], arr[r2]);
break;
}
case 0x03:
{
fprintf(stderr, "sub\n");
sscanf(program + pos, "%x%n", &byte, &consumed);
uint8_t r1 = (uint8_t)byte;
fprintf(stderr, "r1: %d\n", r1);
pos += consumed;
sscanf(program + pos, "%x%n", &byte, &consumed);
uint8_t r2 = (uint8_t)byte;
fprintf(stderr, "r2: %d\n", r2);
pos += consumed;
sub(arr[r1], arr[r2]);
break;
}
case 0x04:
{
fprintf(stderr, "mul\n");
sscanf(program + pos, "%x%n", &byte, &consumed);
uint8_t r1 = (uint8_t)byte;
fprintf(stderr, "r1: %d\n", r1);
pos += consumed;
sscanf(program + pos, "%x%n", &byte, &consumed);
uint8_t r2 = (uint8_t)byte;
fprintf(stderr, "r2: %d\n", r2);
pos += consumed;
mul(arr[r1], arr[r2]);
break;
}
case 0x05:
{
fprintf(stderr, "inc\n");
sscanf(program + pos, "%x%n", &byte, &consumed);
uint8_t r = (uint8_t)byte;
fprintf(stderr, "r1: %d\n", r);
pos += consumed;
inc(arr[r]);
break;
}
case 0x06:
{
fprintf(stderr, "dec\n");
sscanf(program + pos, "%x%n", &byte, &consumed);
uint8_t r = (uint8_t)byte;
fprintf(stderr, "r1: %d\n", r);
pos += consumed;
dec(arr[r]);
break;
}
case 0xFF:
fprintf(stderr, "halt\n");
halted = true;
break;
default:
fprintf(stderr, "unknown opcode\n");
halted = true;
break;
}
}
// Print the final value of each register R0, R1, R2, R3, one value per line
printf("%d\n%d\n%d\n%d\n", R0, R1, R2, R3);
return 0;
} | |
Tested… 100%.