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    if (op->type & (OP_REG | OP_MMX | OP_SSE)) {
        g(0xc0 + (reg << 3) + op->reg);
    } else if (op->reg == -1 && op->reg2 == -1) {
        /* displacement only */
#ifdef TCC_TARGET_X86_64
	g(0x04 + (reg << 3));
	g(0x25);
#else
	g(0x05 + (reg << 3));
#endif
	gen_expr32(&op->e);
#ifdef TCC_TARGET_X86_64
    } else if (op->reg == 8) {
        ExprValue *pe = &op->e;
        g(0x05 + (reg << 3));
        gen_addrpc32(pe->sym ? VT_SYM : 0, pe->sym, pe->v);
        return ind;
#endif
    } else {
        sib_reg1 = op->reg;
        /* fist compute displacement encoding */
        if (sib_reg1 == -1) {
            sib_reg1 = 5;
            mod = 0x00;
        } else if (op->e.v == 0 && !op->e.sym && op->reg != 5) {
            mod = 0x00;
        } else if (op->e.v == (int8_t)op->e.v && !op->e.sym) {
            mod = 0x40;
        } else {
            mod = 0x80;
        }
        /* compute if sib byte needed */
        reg1 = op->reg;
        if (op->reg2 != -1)
            reg1 = 4;
        g(mod + (reg << 3) + reg1);
        if (reg1 == 4) {
            /* add sib byte */
            reg2 = op->reg2;
            if (reg2 == -1)
                reg2 = 4; /* indicate no index */
            g((op->shift << 6) + (reg2 << 3) + sib_reg1);
        }
        /* add offset */
        if (mod == 0x40) {
            g(op->e.v);
        } else if (mod == 0x80 || op->reg == -1) {
	    gen_expr32(&op->e);
        }
    }
    return 0;
}

ST_FUNC void asm_opcode(TCCState *s1, int opcode)
{
    const ASMInstr *pa;
    int i, modrm_index, reg, v, op1, seg_prefix, pc;
    int nb_ops, s;
    Operand ops[MAX_OPERANDS], *pop;
    int op_type[3]; /* decoded op type */
    int alltypes;   /* OR of all operand types */
    int autosize;

    /* force synthetic ';' after prefix instruction, so we can handle */
    /* one-line things like "rep stosb" instead of only "rep\nstosb" */
    if (opcode >= TOK_ASM_wait && opcode <= TOK_ASM_repnz)
        unget_tok(';');

    /* get operands */
    pop = ops;
    nb_ops = 0;
    seg_prefix = 0;
    alltypes = 0;
    for(;;) {
        if (tok == ';' || tok == TOK_LINEFEED)
            break;
        if (nb_ops >= MAX_OPERANDS) {
            tcc_error("incorrect number of operands");
        }
        parse_operand(s1, pop);
        if (tok == ':') {
           if (pop->type != OP_SEG || seg_prefix)
               tcc_error("incorrect prefix");
           seg_prefix = segment_prefixes[pop->reg];
           next();
           parse_operand(s1, pop);
           if (!(pop->type & OP_EA)) {
               tcc_error("segment prefix must be followed by memory reference");
           }
        }
        pop++;
        nb_ops++;
        if (tok != ',')
            break;
        next();
    }

    s = 0; /* avoid warning */

    /* optimize matching by using a lookup table (no hashing is needed
       !) */
    for(pa = asm_instrs; pa->sym != 0; pa++) {
        s = 0;
        if (pa->instr_type & OPC_FARITH) {
            v = opcode - pa->sym;
            if (!((unsigned)v < 8 * 6 && (v % 6) == 0))
                continue;
        } else if (pa->instr_type & OPC_ARITH) {
            if (!(opcode >= pa->sym && opcode < pa->sym + 8*NBWLX))
                continue;
            s = (opcode - pa->sym) % NBWLX;
	    if ((pa->instr_type & OPC_BWLX) == OPC_WLX)
	      {
		/* We need to reject the xxxb opcodes that we accepted above.
		   Note that pa->sym for WLX opcodes is the 'w' token,
		   to get the 'b' token subtract one.  */
		if (((opcode - pa->sym + 1) % NBWLX) == 0)
		    continue;
	        s++;
	      }