A quick Chip8 disassembler using Octo mnemonics.

chip8-disas.c

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

int main()
{
	int addr = 0x200;
	while(!feof(stdin)) {
		uint16_t opcode = (unsigned char)getchar() << 8;
		opcode |= (unsigned char)getchar();
		if(feof(stdin)) { break; } 
		uint16_t lit = opcode & 0xfff;
		uint8_t byte = opcode & 0xff;
		uint8_t nib0 = (opcode & 0xF000) >> 12;
		uint8_t nib1 = (opcode & 0x0F00) >> 8;
		uint8_t nib2 = (opcode & 0xF0) >> 4;
		uint8_t nib3 = opcode & 0xF;
		printf("%04x\t%04x\t", addr, opcode);
		switch(nib0) {
		case 0x0:
			switch(lit) {
			case 0x00E0:
				printf("cls\n"); break;
			case 0x00EE:
				printf("exit\n"); break;
			default:
				printf("syscall 0x%x\n", lit); break;
			}
			break;
		case 0x1:
			printf("jump 0x%x\n", lit); break;
		case 0x2:
			printf("call 0x%x\n", lit); break;
		case 0x3:
			printf("if v%x != %u then\n", nib1, byte); break;
		case 0x4:
			printf("if v%x == %u then\n", nib1, byte); break;
		case 0x5:
			if(nib3 == 0) {
				printf("if v%x != v%x then\n", nib1, nib2);
			} else {
				printf("ill\n");
			}
			break;
		case 0x6:
			printf("v%x := %u\n", nib1, byte); break;
		case 0x7:
			printf("v%x += %u\n", nib1, byte); break;
		case 0x8:
			switch(nib3) {
			case 0x0:
				printf("v%x := v%x\n", nib1, nib2); break;
			case 0x1:
				printf("v%x |= v%x\n", nib1, nib2); break;
			case 0x2:
				printf("v%x &= v%x\n", nib1, nib2); break;
			case 0x3:
				printf("v%x ^= v%x\n", nib1, nib2); break;
			case 0x4:
				printf("v%x += v%x\n", nib1, nib2); break;
			case 0x5:
				printf("v%x -= v%x\n", nib1, nib2); break;
			case 0x6:
				printf("v%x >> 1 (v%x)\n", nib1, nib2); break;
			case 0x7:
				printf("v%x := v%x - v%x\n", nib1, nib2, nib1); break;
			case 0xE:
				printf("v%x << 1 (v%x)\n", nib1, nib2); break;
			default:
				printf("ill\n");
			}
			break;
		case 0x9:
			if(nib3 == 0) {
				printf("if v%x == v%x then\n", nib1, nib2);
			} else {
				printf("ill\n");
			}
			break;
		case 0xA:
			printf("a := 0x%x\n", lit); break;
		case 0xB:
			printf("jump0 %x\n", lit); break;
		case 0xC:
			printf("v%x := rand %x\n", nib1, byte); break;
		case 0xD:
			printf("draw v%x v%x %u\n", nib1, nib2, nib3); break;
		case 0xE:
			switch(byte) {
			case 0x9E:
				printf("if -key v%x then\n", nib1); break;
			case 0xA1:
				printf("if key v%x then\n", nib1); break;
			default:
				printf("ill\n");
			}
			break;
		case 0xF:
			switch(byte) {
			case 0x07:
				printf("v%x := dt\n", nib1); break;
			case 0x0A:
				printf("v%x := key\n", nib1); break;
			case 0x15:
				printf("dt := v%x\n", nib1); break;
			case 0x18:
				printf("st := v%x\n", nib1); break;
			case 0x1E:
				printf("a += v%x\n", nib1); break;
			case 0x29:
				printf("a := hex v%x\n", nib1); break;
			case 0x33:
				printf("bcd v%x\n", nib1); break;
			case 0x55:
				printf("save v%x\n", nib1); break;
			case 0x65:
				printf("load v%x\n", nib1); break;
			default:
				printf("ill\n");
			}
			break;
		}
		addr += 2;
	}
}