disassemble.c

/*
 * Copyright (c) 2012, Brian Swetland
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without 
 * modification, are permitted provided that the following conditions are met:
 *
 *   Redistributions of source code must retain the above copyright notice, 
 *   this list of conditions and the following disclaimer.
 *
 *   Redistributions in binary form must reproduce the above copyright 
 *   notice, this list of conditions and the following disclaimer in the 
 *   documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR 
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT 
 * HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT 
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE 
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 */

/* A DCPU-16 Disassembler */

/* DCPU-16 Spec is Copyright 2012 Mojang */
/* http://0x10c.com/doc/dcpu-16.txt */

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

typedef uint16_t u16;

static const char *opcode[] = {
	"XXX", "MOV", "ADD", "SUB", "MUL", "DIV", "MOD", "SHL",
	"SHR", "AND", "BOR", "XOR", "IFE", "IFN", "IFG", "IFB",
};
static const char regs[8] = "ABCXYZIJ";

static u16 *dis_operand(u16 *pc, u16 n, char *out) {
	if (n < 0x08) {
		sprintf(out,"%c",regs[n & 7]);
	} else if (n < 0x10) {
		sprintf(out,"[%c]",regs[n & 7]);
	} else if (n < 0x18) {
		sprintf(out,"[%c, 0x%04x]",regs[n & 7], *pc++);
	} else if (n > 0x1f) {
		sprintf(out,"%d", n - 0x20);
	} else switch (n) {
		case 0x18: strcpy(out,"POP"); break;
		case 0x19: strcpy(out,"PEEK"); break;
		case 0x1A: strcpy(out,"PUSH"); break;
		case 0x1B: strcpy(out,"SP"); break;
		case 0x1C: strcpy(out,"PC"); break;
		case 0x1D: strcpy(out,"O"); break;
		case 0x1e: sprintf(out,"[0x%04x]",*pc++); break;
		case 0x1f: sprintf(out,"0x%04x",*pc++); break;
	}
	return pc;	
}
u16 *disassemble(u16 *pc, char *out) {
	u16 n = *pc++;
	u16 op = n & 0xF;
	u16 a = (n >> 4) & 0x3F;
	u16 b = (n >> 10);
	if (op > 0) {
		if ((n & 0x03FF) == 0x1C1) {
			sprintf(out,"JMP ");
			pc = dis_operand(pc, b, out+strlen(out));
			return pc;
		}
		sprintf(out,"%s ",opcode[op]);
		pc = dis_operand(pc, a, out+strlen(out));
		sprintf(out+strlen(out),", ");
		pc = dis_operand(pc, b, out+strlen(out)); 
		return pc;
	}
	if (a == 1) {
		sprintf(out,"JSR ");
		pc = dis_operand(pc, b, out+strlen(out));
		return pc;
	}
	sprintf(out,"UNK[%02x] ", a);
	pc = dis_operand(pc, b, out+strlen(out));
	return pc;
}