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refactor(cpu): implement src/chip8.c core logic

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Stevan Freeborn
2026-07-18 15:22:09 -05:00
parent cd6d829670
commit 0e5dfdb808
1 changed files with 247 additions and 0 deletions
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src/chip8.c
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#include "chip8.h"
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
const uint8_t fontset[80] = {
0xF0, 0x90, 0x90, 0x90, 0xF0, // 0
0x20, 0x60, 0x20, 0x20, 0x70, // 1
0xF0, 0x10, 0xF0, 0x80, 0xF0, // 2
0xF0, 0x10, 0xF0, 0x10, 0xF0, // 3
0x90, 0x90, 0xF0, 0x10, 0x10, // 4
0xF0, 0x80, 0xF0, 0x10, 0xF0, // 5
0xF0, 0x80, 0xF0, 0x90, 0xF0, // 6
0xF0, 0x10, 0x20, 0x40, 0x40, // 7
0xF0, 0x90, 0xF0, 0x90, 0xF0, // 8
0xF0, 0x90, 0xF0, 0x10, 0xF0, // 9
0xF0, 0x90, 0xF0, 0x90, 0x90, // A
0xE0, 0x90, 0xE0, 0x90, 0xE0, // B
0xF0, 0x80, 0x80, 0x80, 0xF0, // C
0xE0, 0x90, 0x90, 0x90, 0xE0, // D
0xF0, 0x80, 0xF0, 0x80, 0xF0, // E
0xF0, 0x80, 0xF0, 0x80, 0x80 // F
};
void chip8_init(chip_eight_t *chip) {
memset(chip, 0, sizeof(chip_eight_t));
chip->pc = PROGRAM_START;
chip->dt = 0;
chip->st = 0;
chip->waiting_for_key = false;
for (int i = 0; i < 80; i++) {
chip->memory[FONT_START + i] = fontset[i];
}
}
int chip8_load_rom(chip_eight_t *chip, const char *file_path) {
FILE *file_ptr = fopen(file_path, "rb");
if (file_ptr == NULL) {
return FILE_MISSING;
}
fseek(file_ptr, 0, SEEK_END);
int num_of_bytes = ftell(file_ptr);
int max_program_size = MEMORY_SIZE - PROGRAM_START;
if (num_of_bytes > max_program_size) {
fclose(file_ptr);
return PROGRAM_TOO_LARGE;
}
fseek(file_ptr, 0, SEEK_SET);
size_t bytes_read = fread(&chip->memory[PROGRAM_START], sizeof(uint8_t), num_of_bytes, file_ptr);
(void)bytes_read; // Ignore unused warning
fclose(file_ptr);
return COMPLETED_SUCCESSFULLY;
}
static void draw_sprite(chip_eight_t *chip, uint16_t n, uint16_t x, uint16_t y) {
uint8_t x_coordinate = chip->V[x] % SCREEN_WIDTH;
uint8_t y_coordinate = chip->V[y] % SCREEN_HEIGHT;
chip->V[15] = 0;
for (int row = 0; row < n; row++) {
uint8_t sprite_byte = chip->memory[chip->I + row];
if ((y_coordinate + row) >= SCREEN_HEIGHT) {
break;
}
for (int col = 0; col < 8; col++) {
if ((x_coordinate + col) >= SCREEN_WIDTH) {
break;
}
uint8_t sprite_pixel = sprite_byte & (128 >> col);
int sprite_screen_index = ((y_coordinate + row) * SCREEN_WIDTH) + (x_coordinate + col);
uint32_t *screen_pixel = &chip->display[sprite_screen_index];
if (sprite_pixel != 0) {
if (*screen_pixel == 1) {
chip->V[15] = 1;
}
*screen_pixel ^= 1;
}
}
}
}
void chip8_step(chip_eight_t *chip) {
if (chip->waiting_for_key) {
return;
}
uint16_t opcode = (chip->memory[chip->pc] << 8) | (chip->memory[chip->pc + 1]);
chip->pc += 2;
uint16_t nnn = opcode & 4095;
uint8_t nn = opcode & 255;
uint16_t n = opcode & 15;
uint16_t x = (opcode & 3840) >> 8;
uint16_t y = (opcode & 240) >> 4;
uint16_t kk = opcode & 255;
switch(opcode & 61440) {
case OPCODE_GROUP_SYS_OR_RET:
if (opcode == OPCODE_CLS) {
memset(chip->display, 0, sizeof(chip->display));
} else if (opcode == OPCODE_RET) {
chip->sc -= 1;
chip->pc = chip->stack[chip->sc];
}
break;
case OPCODE_GROUP_JUMP:
chip->pc = nnn;
break;
case OPCODE_GROUP_CALL:
chip->stack[chip->sc] = chip->pc;
chip->sc += 1;
chip->pc = nnn;
break;
case OPCODE_GROUP_SE_VX_BYTE:
if (chip->V[x] == kk) {
chip->pc += 2;
}
break;
case OPCODE_GROUP_SNE_VX_BYTE:
if (chip->V[x] != kk) {
chip->pc += 2;
}
break;
case OPCODE_GROUP_SE_VX_VY:
if (chip->V[x] == chip->V[y]) {
chip->pc += 2;
}
break;
case OPCODE_GROUP_LD_VX_BYTE:
chip->V[x] = kk;
break;
case OPCODE_GROUP_ADD_VX_BYTE:
chip->V[x] += kk;
break;
case OPCODE_GROUP_ARITHMETIC:
if (n == SUB_OP_LD) {
chip->V[x] = chip->V[y];
} else if (n == SUB_OP_OR) {
chip->V[x] = chip->V[x] | chip->V[y];
} else if (n == SUB_OP_AND) {
chip->V[x] = chip->V[x] & chip->V[y];
} else if (n == SUB_OP_XOR) {
chip->V[x] = chip->V[x] ^ chip->V[y];
} else if (n == SUB_OP_ADD) {
uint16_t r = chip->V[x] + chip->V[y];
chip->V[15] = (r > 255) ? 1 : 0;
chip->V[x] = r & 255;
} else if (n == SUB_OP_SUB) {
chip->V[15] = (chip->V[x] >= chip->V[y]) ? 1 : 0;
chip->V[x] = chip->V[x] - chip->V[y];
} else if (n == SUB_OP_SHR) {
uint8_t flag = chip->V[x] & 1;
chip->V[15] = flag;
chip->V[x] /= 2;
} else if (n == SUB_OP_SUBN) {
chip->V[15] = (chip->V[y] >= chip->V[x]) ? 1 : 0;
chip->V[x] = chip->V[y] - chip->V[x];
} else if (n == SUB_OP_SHL) {
uint8_t flag = (chip->V[x] & 128) >> 7;
chip->V[15] = flag;
chip->V[x] *= 2;
}
break;
case OPCODE_GROUP_SNE_VX_VY:
if (chip->V[x] != chip->V[y]) {
chip->pc += 2;
}
break;
case OPCODE_GROUP_LD_I_ADDR:
chip->I = nnn;
break;
case OPCODE_GROUP_JP_V0_ADDR:
chip->pc = nnn + chip->V[0];
break;
case OPCODE_GROUP_RND_VX_BYTE:
uint8_t num = rand() % 256;
chip->V[x] = kk & num;
break;
case OPCODE_GROUP_DRW_VX_VY_N:
draw_sprite(chip, n, x, y);
break;
case OPCODE_GROUP_KEY_SKIP:
if (nn == OPCODE_SKP) {
if (chip->keys[chip->V[x] & 0x0F] == 1) {
chip->pc += 2;
}
} else if (nn == OPCODE_SKNP) {
if (chip->keys[chip->V[x] & 0x0F] != 1) {
chip->pc += 2;
}
}
break;
case OPCODE_GROUP_MISC:
if (nn == SUB_OP_LD_VX_DT) {
chip->V[x] = chip->dt;
} else if (nn == SUB_OP_LD_VX_K) {
chip->waiting_for_key = true;
chip->key_register = x;
} else if (nn == SUB_OP_LD_DT_VX) {
chip->dt = chip->V[x];
} else if (nn == SUB_OP_LD_ST_VX) {
chip->st = chip->V[x];
} else if (nn == SUB_OP_ADD_I_VX) {
chip->I += chip->V[x];
} else if (nn == SUB_OP_LD_F_VX) {
chip->I = FONT_START + ((chip->V[x] & 0x0F) * 5);
} else if (nn == SUB_OP_LD_B_VX) {
chip->memory[chip->I] = chip->V[x] / 100;
chip->memory[chip->I + 1] = (chip->V[x] / 10) % 10;
chip->memory[chip->I + 2] = chip->V[x] % 10;
} else if (nn == SUB_OP_LD_I_REG) {
for (int i = 0; i <= x; i++) {
chip->memory[chip->I + i] = chip->V[i];
}
} else if (nn == SUB_OP_LD_REG_I) {
for (int i = 0; i <= x; i++) {
chip->V[i] = chip->memory[chip->I + i];
}
}
break;
default:
break;
}
}
void chip8_tick_timers(chip_eight_t *chip) {
if (chip->dt > 0) {
chip->dt--;
}
if (chip->st > 0) {
chip->st--;
}
}