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/* assemble.c   code generation for the Netwide Assembler
 *
 * The Netwide Assembler is copyright (C) 1996 Simon Tatham and
 * Julian Hall. All rights reserved. The software is
 * redistributable under the licence given in the file "Licence"
 * distributed in the NASM archive.
 *
 * the actual codes (C syntax, i.e. octal):
 * \0            - terminates the code. (Unless it's a literal of course.)
 * \1, \2, \3    - that many literal bytes follow in the code stream
 * \4, \6        - the POP/PUSH (respectively) codes for CS, DS, ES, SS
 *                 (POP is never used for CS) depending on operand 0
 * \5, \7        - the second byte of POP/PUSH codes for FS, GS, depending
 *                 on operand 0
 * \10, \11, \12 - a literal byte follows in the code stream, to be added
 *                 to the register value of operand 0, 1 or 2
 * \17           - encodes the literal byte 0. (Some compilers don't take
 *                 kindly to a zero byte in the _middle_ of a compile time
 *                 string constant, so I had to put this hack in.)
 * \14, \15, \16 - a signed byte immediate operand, from operand 0, 1 or 2
 * \20, \21, \22 - a byte immediate operand, from operand 0, 1 or 2
 * \24, \25, \26 - an unsigned byte immediate operand, from operand 0, 1 or 2
 * \30, \31, \32 - a word immediate operand, from operand 0, 1 or 2
 * \34, \35, \36 - select between \3[012] and \4[012] depending on 16/32 bit
 *                 assembly mode or the address-size override on the operand
 * \37           - a word constant, from the _segment_ part of operand 0
 * \40, \41, \42 - a long immediate operand, from operand 0, 1 or 2
 * \50, \51, \52 - a byte relative operand, from operand 0, 1 or 2
 * \60, \61, \62 - a word relative operand, from operand 0, 1 or 2
 * \64, \65, \66 - select between \6[012] and \7[012] depending on 16/32 bit
 *                 assembly mode or the address-size override on the operand
 * \70, \71, \72 - a long relative operand, from operand 0, 1 or 2
 * \1ab          - a ModRM, calculated on EA in operand a, with the spare
 *                 field the register value of operand b.
 * \2ab          - a ModRM, calculated on EA in operand a, with the spare
 *                 field equal to digit b.
 * \30x          - might be an 0x67 byte, depending on the address size of
 *                 the memory reference in operand x.
 * \310          - indicates fixed 16-bit address size, i.e. optional 0x67.
 * \311          - indicates fixed 32-bit address size, i.e. optional 0x67.
 * \320          - indicates fixed 16-bit operand size, i.e. optional 0x66.
 * \321          - indicates fixed 32-bit operand size, i.e. optional 0x66.
 * \322          - indicates that this instruction is only valid when the
 *                 operand size is the default (instruction to disassembler,
 *                 generates no code in the assembler)
 * \330          - a literal byte follows in the code stream, to be added
 *                 to the condition code value of the instruction.
 * \340          - reserve <operand 0> bytes of uninitialised storage.
 *                 Operand 0 had better be a segmentless constant.
 */

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

#include "nasm.h"
#include "assemble.h"
#include "insns.h"

extern struct itemplate *nasm_instructions[];

typedef struct {
    int sib_present;		       /* is a SIB byte necessary? */
    int bytes;			       /* # of bytes of offset needed */
    int size;			       /* lazy - this is sib+bytes+1 */
    unsigned char modrm, sib;	       /* the bytes themselves */
} ea;

static efunc errfunc;
static struct ofmt *outfmt;

static long calcsize (long, long, int, insn *, char *);
static void gencode (long, long, int, insn *, char *, long);
static int regval (operand *o);
static int matches (struct itemplate *, insn *);
static ea *process_ea (operand *, ea *, int, int, int);
static int chsize (operand *, int);

long assemble (long segment, long offset, int bits,
	       insn *instruction, struct ofmt *output, efunc error) {
    int j, itimes, size_prob;
    long insn_end;
    long start = offset;
    struct itemplate *temp;

    errfunc = error;		       /* to pass to other functions */
    outfmt = output;		       /* likewise */

    if (instruction->opcode == -1)
    	return 0;

    if (instruction->opcode == I_DB ||
	instruction->opcode == I_DW ||
	instruction->opcode == I_DD ||
	instruction->opcode == I_DQ ||
	instruction->opcode == I_DT) {
	extop *e;
	long osize, wsize = 0;	       /* placate gcc */
	int t = instruction->times;

	switch (instruction->opcode) {
	  case I_DB: wsize = 1; break;
	  case I_DW: wsize = 2; break;
	  case I_DD: wsize = 4; break;
	  case I_DQ: wsize = 8; break;
	  case I_DT: wsize = 10; break;
	}

	while (t--) {
	    for (e = instruction->eops; e; e = e->next) {
		osize = 0;
		if (e->type == EOT_DB_NUMBER) {
		    if (wsize == 1) {
			if (e->segment != NO_SEG)
			    errfunc (ERR_NONFATAL,
				     "one-byte relocation attempted");
			else {
			    unsigned char c = e->offset;
			    outfmt->output (segment, &c, OUT_RAWDATA+1,
					    NO_SEG, NO_SEG);
			}
		    } else if (wsize > 5) {
			errfunc (ERR_NONFATAL, "integer supplied to a D%c"
				 " instruction", wsize==8 ? 'Q' : 'T');
		    } else
			outfmt->output (segment, &e->offset,
					OUT_ADDRESS+wsize, e->segment,
					e->wrt);
		    offset += wsize;
		} else if (e->type == EOT_DB_STRING) {
		    int align;

		    align = (-e->stringlen) % wsize;
		    if (align < 0)
			align += wsize;
		    outfmt->output (segment, e->stringval,
				    OUT_RAWDATA+e->stringlen, NO_SEG, NO_SEG);
		    if (align)
			outfmt->output (segment, "\0\0\0\0",
					OUT_RAWDATA+align, NO_SEG, NO_SEG);
		    offset += e->stringlen + align;
		}
	    }
	}
	return offset - start;
    }

    size_prob = FALSE;
    temp = nasm_instructions[instruction->opcode];
    while (temp->opcode != -1) {
	int m = matches (temp, instruction);
	if (m == 100) {		       /* matches! */
	    char *codes = temp->code;
	    long insn_size = calcsize(segment, offset, bits,
				      instruction, codes);
	    itimes = instruction->times;
	    if (insn_size < 0)	       /* shouldn't be, on pass two */
	    	error (ERR_PANIC, "errors made it through from pass one");
	    else while (itimes--) {
		insn_end = offset + insn_size;
		for (j=0; j<instruction->nprefix; j++) {
		    unsigned char c;
		    switch (instruction->prefixes[j]) {
		      case P_LOCK:
			c = 0xF0; break;
		      case P_REPNE: case P_REPNZ:
			c = 0xF2; break;
		      case P_REPE: case P_REPZ: case P_REP:
			c = 0xF3; break;
		      case R_CS: c = 0x2E; break;
		      case R_DS: c = 0x3E; break;
		      case R_ES: c = 0x26; break;
		      case R_FS: c = 0x64; break;
		      case R_GS: c = 0x65; break;
		      case R_SS: c = 0x36; break;
		      case P_A16:
			if (bits == 16)
			    c = 0;     /* no prefix */
			else
			    c = 0x67;
			break;
		      case P_A32:
			if (bits == 32)
			    c = 0;     /* no prefix */
			else
			    c = 0x67;
			break;
		      case P_O16:
			if (bits == 16)
			    c = 0;     /* no prefix */
			else
			    c = 0x66;
			break;
		      case P_O32:
			if (bits == 32)
			    c = 0;     /* no prefix */
			else
			    c = 0x66;
			break;
		      default:
			error (ERR_PANIC,
			       "invalid instruction prefix");
		    }
		    if (c != 0)
			outfmt->output (segment, &c, OUT_RAWDATA+1,
					NO_SEG, NO_SEG);
		    offset++;
		}
		gencode (segment, offset, bits, instruction, codes, insn_end);
		offset += insn_size;
	    }
	    return offset - start;
	} else if (m > 0) {
	    size_prob = m;
	}
	temp++;
    }
    if (temp->opcode == -1) {	       /* didn't match any instruction */
	if (size_prob == 1)	       /* would have matched, but for size */
	    error (ERR_NONFATAL, "operation size not specified");
	else if (size_prob == 2)
	    error (ERR_NONFATAL, "mismatch in operand sizes");
	else
	    error (ERR_NONFATAL,
		   "invalid combination of opcode and operands");
    }
    return 0;
}

long insn_size (long segment, long offset, int bits,
		insn *instruction, efunc error) {
    struct itemplate *temp;

    errfunc = error;		       /* to pass to other functions */

    if (instruction->opcode == -1)
    	return 0;

    if (instruction->opcode == I_DB ||
	instruction->opcode == I_DW ||
	instruction->opcode == I_DD ||
	instruction->opcode == I_DQ ||
	instruction->opcode == I_DT) {
	extop *e;
	long isize, osize, wsize = 0;  /* placate gcc */

	isize = 0;
	switch (instruction->opcode) {
	  case I_DB: wsize = 1; break;
	  case I_DW: wsize = 2; break;
	  case I_DD: wsize = 4; break;
	  case I_DQ: wsize = 8; break;
	  case I_DT: wsize = 10; break;
	}

	for (e = instruction->eops; e; e = e->next) {
	    long align;

	    osize = 0;
	    if (e->type == EOT_DB_NUMBER)
		osize = 1;
	    else if (e->type == EOT_DB_STRING)
		osize = e->stringlen;

	    align = (-osize) % wsize;
	    if (align < 0)
		align += wsize;
	    isize += osize + align;
	}
	return isize * instruction->times;
    }

    temp = nasm_instructions[instruction->opcode];
    while (temp->opcode != -1) {
	if (matches(temp, instruction) == 100) {
	    /* we've matched an instruction. */
	    long isize;
	    char *codes = temp->code;
	    int j;

	    isize = calcsize(segment, offset, bits, instruction, codes);
	    if (isize < 0)
	    	return -1;
	    for (j = 0; j < instruction->nprefix; j++) {
		if ((instruction->prefixes[j] != P_A16 &&
		     instruction->prefixes[j] != P_O16 && bits==16) ||
		    (instruction->prefixes[j] != P_A32 &&
		     instruction->prefixes[j] != P_O32 && bits==32))
		    isize++;
	    }
	    return isize * instruction->times;
	}
	temp++;
    }
    return -1;			       /* didn't match any instruction */
}

static long calcsize (long segment, long offset, int bits,
		      insn *ins, char *codes) {
    long length = 0;
    unsigned char c;

    while (*codes) switch (c = *codes++) {
      case 01: case 02: case 03:
	codes += c, length += c; break;
      case 04: case 05: case 06: case 07:
	length++; break;
      case 010: case 011: case 012:
	codes++, length++; break;
      case 017:
	length++; break;
      case 014: case 015: case 016:
	length++; break;
      case 020: case 021: case 022:
	length++; break;
      case 024: case 025: case 026:
	length++; break;
      case 030: case 031: case 032:
	length += 2; break;
      case 034: case 035: case 036:
	length += ((ins->oprs[c-034].addr_size ?
		    ins->oprs[c-034].addr_size : bits) == 16 ? 2 : 4); break;
      case 037:
	length += 2; break;
      case 040: case 041: case 042:
	length += 4; break;
      case 050: case 051: case 052:
	length++; break;
      case 060: case 061: case 062:
	length += 2; break;
      case 064: case 065: case 066:
	length += ((ins->oprs[c-064].addr_size ?
		    ins->oprs[c-064].addr_size : bits) == 16 ? 2 : 4); break;
      case 070: case 071: case 072:
	length += 4; break;
      case 0300: case 0301: case 0302:
	length += chsize (&ins->oprs[c-0300], bits);
	break;
      case 0310:
	length += (bits==32);
	break;
      case 0311:
	length += (bits==16);
	break;
      case 0312:
	break;
      case 0320:
	length += (bits==32);
	break;
      case 0321:
	length += (bits==16);
	break;
      case 0322:
	break;
      case 0330:
	codes++, length++; break;
      case 0340: case 0341: case 0342:
	if (ins->oprs[0].segment != NO_SEG)
	    errfunc (ERR_NONFATAL, "attempt to reserve non-constant"
		     " quantity of BSS space");
	else
	    length += ins->oprs[0].offset << (c-0340);
	break;
      default:			       /* can't do it by 'case' statements */
	if (c>=0100 && c<=0277) {      /* it's an EA */
	    ea ea_data;
	    if (!process_ea (&ins->oprs[(c>>3)&7], &ea_data, bits, 0,
			     ins->forw_ref)) {
	    	errfunc (ERR_NONFATAL, "invalid effective address");
		return -1;
	    } else
	    	length += ea_data.size;
	} else
	    errfunc (ERR_PANIC, "internal instruction table corrupt"
		     ": instruction code 0x%02X given", c);
    }
    return length;
}

static void gencode (long segment, long offset, int bits,
		     insn *ins, char *codes, long insn_end) {
    static char condval[] = { /* conditional opcodes */
	0x7, 0x3, 0x2, 0x6, 0x2, 0x4, 0xF, 0xD, 0xC, 0xE, 0x6, 0x2,
	0x3, 0x7, 0x3, 0x5, 0xE, 0xC, 0xD, 0xF, 0x1, 0xB, 0x9, 0x5,
	0x0, 0xA, 0xA, 0xB, 0x8, 0x4
    };
    unsigned char c, bytes[4];
    long data, size;

    while (*codes) switch (c = *codes++) {
      case 01: case 02: case 03:
	outfmt->output (segment, codes, OUT_RAWDATA+c, NO_SEG, NO_SEG);
	codes += c;
	offset += c;
	break;
      case 04: case 06:
	switch (ins->oprs[0].basereg) {
	  case R_CS: bytes[0] = 0x0E + (c == 0x04 ? 1 : 0); break;
	  case R_DS: bytes[0] = 0x1E + (c == 0x04 ? 1 : 0); break;
	  case R_ES: bytes[0] = 0x06 + (c == 0x04 ? 1 : 0); break;
	  case R_SS: bytes[0] = 0x16 + (c == 0x04 ? 1 : 0); break;
	  default:
	    errfunc (ERR_PANIC, "bizarre 8086 segment register received");
	}
	outfmt->output (segment, bytes, OUT_RAWDATA+1, NO_SEG, NO_SEG);
	offset++;
	break;
      case 05: case 07:
	switch (ins->oprs[0].basereg) {
	  case R_FS: bytes[0] = 0xA0 + (c == 0x05 ? 1 : 0); break;
	  case R_GS: bytes[0] = 0xA8 + (c == 0x05 ? 1 : 0); break;
	  default:
	    errfunc (ERR_PANIC, "bizarre 386 segment register received");
	}
	outfmt->output (segment, bytes, OUT_RAWDATA+1, NO_SEG, NO_SEG);
	offset++;
	break;
      case 010: case 011: case 012:
	bytes[0] = *codes++ + regval(&ins->oprs[c-010]);
	outfmt->output (segment, bytes, OUT_RAWDATA+1, NO_SEG, NO_SEG);
	offset += 1;
	break;
      case 017:
	bytes[0] = 0;
	outfmt->output (segment, bytes, OUT_RAWDATA+1, NO_SEG, NO_SEG);
	offset += 1;
	break;
      case 014: case 015: case 016:
	if (ins->oprs[c-014].offset < -128 || ins->oprs[c-014].offset > 127)
	    errfunc (ERR_WARNING, "signed byte value exceeds bounds");
	bytes[0] = ins->oprs[c-014].offset;
	outfmt->output (segment, bytes, OUT_RAWDATA+1, NO_SEG, NO_SEG);
	offset += 1;
	break;
      case 020: case 021: case 022:
	if (ins->oprs[c-020].offset < -128 || ins->oprs[c-020].offset > 255)
	    errfunc (ERR_WARNING, "byte value exceeds bounds");
	bytes[0] = ins->oprs[c-020].offset;
	outfmt->output (segment, bytes, OUT_RAWDATA+1, NO_SEG, NO_SEG);
	offset += 1;
	break;
      case 024: case 025: case 026:
	if (ins->oprs[c-024].offset < 0 || ins->oprs[c-024].offset > 255)
	    errfunc (ERR_WARNING, "unsigned byte value exceeds bounds");
	bytes[0] = ins->oprs[c-024].offset;
	outfmt->output (segment, bytes, OUT_RAWDATA+1, NO_SEG, NO_SEG);
	offset += 1;
	break;
      case 030: case 031: case 032:
	if (ins->oprs[c-030].segment == NO_SEG &&
	    ins->oprs[c-030].wrt == NO_SEG &&
	    (ins->oprs[c-030].offset < -32768 ||
	    ins->oprs[c-030].offset > 65535))
	    errfunc (ERR_WARNING, "word value exceeds bounds");
	data = ins->oprs[c-030].offset;
	outfmt->output (segment, &data, OUT_ADDRESS+2,
			ins->oprs[c-030].segment, ins->oprs[c-030].wrt);
	offset += 2;
	break;
      case 034: case 035: case 036:
	data = ins->oprs[c-034].offset;
	size = ((ins->oprs[c-034].addr_size ?
		 ins->oprs[c-034].addr_size : bits) == 16 ? 2 : 4);
	if (size==16 && (data < -32768 || data > 65535))
	    errfunc (ERR_WARNING, "word value exceeds bounds");
	outfmt->output (segment, &data, OUT_ADDRESS+size,
			ins->oprs[c-034].segment, ins->oprs[c-034].wrt);
	offset += size;
	break;
      case 037:
	if (ins->oprs[0].segment == NO_SEG)
	    errfunc (ERR_NONFATAL, "value referenced by FAR is not"
		     " relocatable");
	data = 0L;
	outfmt->output (segment, &data, OUT_ADDRESS+2,
			outfmt->segbase(1+ins->oprs[0].segment),
			ins->oprs[0].wrt);
	offset += 2;
	break;
      case 040: case 041: case 042:
	data = ins->oprs[c-040].offset;
	outfmt->output (segment, &data, OUT_ADDRESS+4,
			ins->oprs[c-040].segment, ins->oprs[c-040].wrt);
	offset += 4;
	break;
      case 050: case 051: case 052:
	if (ins->oprs[c-050].segment != segment)
	    errfunc (ERR_NONFATAL, "short relative jump outside segment");
	data = ins->oprs[c-050].offset - insn_end;
	if (data > 127 || data < -128)
	    errfunc (ERR_NONFATAL, "short jump is out of range");
	bytes[0] = data;
	outfmt->output (segment, bytes, OUT_RAWDATA+1, NO_SEG, NO_SEG);
	offset += 1;
	break;
      case 060: case 061: case 062:
	if (ins->oprs[c-060].segment != segment) {
	    data = ins->oprs[c-060].offset;
	    outfmt->output (segment, &data, OUT_REL2ADR+insn_end-offset,
			    ins->oprs[c-060].segment, ins->oprs[c-060].wrt);
	} else {
	    data = ins->oprs[c-060].offset - insn_end;
	    outfmt->output (segment, &data, OUT_ADDRESS+2, NO_SEG, NO_SEG);
	}
	offset += 2;
	break;
      case 064: case 065: case 066:
	size = ((ins->oprs[c-064].addr_size ?
		 ins->oprs[c-064].addr_size : bits) == 16 ? 2 : 4);
	if (ins->oprs[c-064].segment != segment) {
	    data = ins->oprs[c-064].offset;
	    size = (bits == 16 ? OUT_REL2ADR : OUT_REL4ADR);
	    outfmt->output (segment, &data, size+insn_end-offset,
			    ins->oprs[c-064].segment, ins->oprs[c-064].wrt);
	    size = (bits == 16 ? 2 : 4);
	} else {
	    data = ins->oprs[c-064].offset - insn_end;
	    outfmt->output (segment, &data, OUT_ADDRESS+size, NO_SEG, NO_SEG);
	}
	offset += size;
	break;
      case 070: case 071: case 072:
	if (ins->oprs[c-070].segment != segment) {
	    data = ins->oprs[c-070].offset;
	    outfmt->output (segment, &data, OUT_REL4ADR+insn_end-offset,
			    ins->oprs[c-070].segment, ins->oprs[c-070].wrt);
	} else {
	    data = ins->oprs[c-070].offset - insn_end;
	    outfmt->output (segment, &data, OUT_ADDRESS+4, NO_SEG, NO_SEG);
	}
	offset += 4;
	break;
      case 0300: case 0301: case 0302:
	if (chsize (&ins->oprs[c-0300], bits)) {
	    *bytes = 0x67;
	    outfmt->output (segment, bytes, OUT_RAWDATA+1, NO_SEG, NO_SEG);
	    offset += 1;
	} else
	    offset += 0;
	break;
      case 0310:
	if (bits==32) {
	    *bytes = 0x67;
	    outfmt->output (segment, bytes, OUT_RAWDATA+1, NO_SEG, NO_SEG);
	    offset += 1;
	} else
	    offset += 0;
	break;
      case 0311:
	if (bits==16) {
	    *bytes = 0x67;
	    outfmt->output (segment, bytes, OUT_RAWDATA+1, NO_SEG, NO_SEG);
	    offset += 1;
	} else
	    offset += 0;
	break;
      case 0312:
	break;
      case 0320:
	if (bits==32) {
	    *bytes = 0x66;
	    outfmt->output (segment, bytes, OUT_RAWDATA+1, NO_SEG, NO_SEG);
	    offset += 1;
	} else
	    offset += 0;
	break;
      case 0321:
	if (bits==16) {
	    *bytes = 0x66;
	    outfmt->output (segment, bytes, OUT_RAWDATA+1, NO_SEG, NO_SEG);
	    offset += 1;
	} else
	    offset += 0;
	break;
      case 0322:
	break;
      case 0330:
	*bytes = *codes++ + condval[ins->condition];
	outfmt->output (segment, bytes, OUT_RAWDATA+1, NO_SEG, NO_SEG);
	offset += 1;
	break;
      case 0340: case 0341: case 0342:
	if (ins->oprs[0].segment != NO_SEG)
	    errfunc (ERR_PANIC, "non-constant BSS size in pass two");
	else {
	    long size = ins->oprs[0].offset << (c-0340);
	    outfmt->output (segment, NULL, OUT_RESERVE+size, NO_SEG, NO_SEG);
	    offset += size;
	}
	break;
      default:			       /* can't do it by 'case' statements */
	if (c>=0100 && c<=0277) {      /* it's an EA */
	    ea ea_data;
	    int rfield;
	    unsigned char *p;
	    long s;

	    if (c<=0177)	       /* pick rfield from operand b */
		rfield = regval (&ins->oprs[c&7]);
	    else 		       /* rfield is constant */
	    	rfield = c & 7;
	    if (!process_ea (&ins->oprs[(c>>3)&7], &ea_data, bits, rfield,
			     ins->forw_ref))
	    	errfunc (ERR_NONFATAL, "invalid effective address");

	    p = bytes;
	    *p++ = ea_data.modrm;
	    if (ea_data.sib_present)
	    	*p++ = ea_data.sib;
	    /*
	     * the cast in the next line is to placate MS C...
	     */
	    outfmt->output (segment, bytes, OUT_RAWDATA+(long)(p-bytes),
			    NO_SEG, NO_SEG);
	    s = p-bytes;

	    switch (ea_data.bytes) {
	      case 0:
		break;
	      case 1:
	        *bytes = ins->oprs[(c>>3)&7].offset;
		outfmt->output (segment, bytes, OUT_RAWDATA+1,
				NO_SEG, NO_SEG);
		s++;
		break;
	      case 2:
	      case 4:
		data = ins->oprs[(c>>3)&7].offset;
		outfmt->output (segment, &data, OUT_ADDRESS+ea_data.bytes,
				ins->oprs[(c>>3)&7].segment,
				ins->oprs[(c>>3)&7].wrt);
		s += ea_data.bytes;
		break;
	    }
	    offset += s;
	} else
	    errfunc (ERR_PANIC, "internal instruction table corrupt"
		     ": instruction code 0x%02X given", c);
    }
}

static int regval (operand *o) {
    switch (o->basereg) {
      case R_EAX: case R_AX: case R_AL: case R_ES: case R_CR0: case R_DR0:
      case R_ST0: case R_MM0:
	return 0;
      case R_ECX: case R_CX: case R_CL: case R_CS: case R_DR1: case R_ST1:
      case R_MM1:
	return 1;
      case R_EDX: case R_DX: case R_DL: case R_SS: case R_CR2: case R_DR2:
      case R_ST2: case R_MM2:
	return 2;
      case R_EBX: case R_BX: case R_BL: case R_DS: case R_CR3: case R_DR3:
      case R_TR3: case R_ST3: case R_MM3:
	return 3;
      case R_ESP: case R_SP: case R_AH: case R_FS: case R_CR4: case R_TR4:
      case R_ST4: case R_MM4:
	return 4;
      case R_EBP: case R_BP: case R_CH: case R_GS: case R_TR5: case R_ST5:
      case R_MM5:
	return 5;
      case R_ESI: case R_SI: case R_DH: case R_DR6: case R_TR6: case R_ST6:
      case R_MM6:
	return 6;
      case R_EDI: case R_DI: case R_BH: case R_DR7: case R_TR7: case R_ST7:
      case R_MM7:
	return 7;
      default:			       /* panic */
	errfunc (ERR_PANIC, "invalid register operand given to regval()");
	return 0;
    }
}

static int matches (struct itemplate *itemp, insn *instruction) {
    int i, size, oprs, ret;

    ret = 100;

    /*
     * Check the opcode
     */
    if (itemp->opcode != instruction->opcode) return 0;

    /*
     * Count the operands
     */
    if (itemp->operands != instruction->operands) return 0;

    /*
     * Check that no spurious colons or TOs are present
     */
    for (i=0; i<itemp->operands; i++)
	if (instruction->oprs[i].type & ~itemp->opd[i] & (COLON|TO))
	    return 0;

    /*
     * Check that the operand flags all match up
     */
    for (i=0; i<itemp->operands; i++)
	if (itemp->opd[i] & ~instruction->oprs[i].type ||
	    ((itemp->opd[i] & SIZE_MASK) &&
	     ((itemp->opd[i] ^ instruction->oprs[i].type) & SIZE_MASK))) {
	    if ((itemp->opd[i] & ~instruction->oprs[i].type & NON_SIZE) ||
		(instruction->oprs[i].type & SIZE_MASK))
		return 0;
	    else
		ret = 1;
	}

    /*
     * Check operand sizes
     */
    if (itemp->flags & IF_SB) {
	size = BITS8;
	oprs = itemp->operands;
    } else if (itemp->flags & IF_SD) {
	size = BITS32;
	oprs = itemp->operands;
    } else if (itemp->flags & (IF_SM | IF_SM2)) {
	oprs = (itemp->flags & IF_SM2 ? 2 : itemp->operands);
	size = 0;		       /* placate gcc */
	for (i=0; i<oprs; i++)
	    if ( (size = itemp->opd[i] & SIZE_MASK) != 0)
		break;
    } else {
	size = 0;
	oprs = itemp->operands;
    }

    for (i=0; i<itemp->operands; i++)
	if (!(itemp->opd[i] & SIZE_MASK) &&
	    (instruction->oprs[i].type & SIZE_MASK & ~size))
	    ret = 2;

    return ret;
}

static ea *process_ea (operand *input, ea *output, int addrbits, int rfield,
		       int forw_ref) {
    if (!(REGISTER & ~input->type)) {  /* it's a single register */
	static int regs[] = {
	    R_MM0, R_EAX, R_AX, R_AL, R_MM1, R_ECX, R_CX, R_CL,
	    R_MM2, R_EDX, R_DX, R_DL, R_MM3, R_EBX, R_BX, R_BL,
	    R_MM4, R_ESP, R_SP, R_AH, R_MM5, R_EBP, R_BP, R_CH,
	    R_MM6, R_ESI, R_SI, R_DH, R_MM7, R_EDI, R_DI, R_BH
	};
	int i;

	for (i=0; i<elements(regs); i++)
	    if (input->basereg == regs[i]) break;
	if (i<elements(regs)) {
	    output->sib_present = FALSE;/* no SIB necessary */
	    output->bytes = 0;	       /* no offset necessary either */
	    output->modrm = 0xC0 | (rfield << 3) | (i/4);
	} else
	    return NULL;
    } else {			       /* it's a memory reference */
	if (input->basereg==-1 && (input->indexreg==-1 || input->scale==0)) {
	    /* it's a pure offset */
	    if (input->addr_size)
		addrbits = input->addr_size;
	    output->sib_present = FALSE;
	    output->bytes = (addrbits==32 ? 4 : 2);
	    output->modrm = (addrbits==32 ? 5 : 6) | (rfield << 3);
	} else {		       /* it's an indirection */
	    int i=input->indexreg, b=input->basereg, s=input->scale;
	    long o=input->offset, seg=input->segment;

	    if (s==0) i = -1;	       /* make this easy, at least */

	    if (i==R_EAX || i==R_EBX || i==R_ECX || i==R_EDX
		|| i==R_EBP || i==R_ESP || i==R_ESI || i==R_EDI
		|| b==R_EAX || b==R_EBX || b==R_ECX || b==R_EDX
		|| b==R_EBP || b==R_ESP || b==R_ESI || b==R_EDI) {
		/* it must be a 32-bit memory reference. Firstly we have
		 * to check that all registers involved are type Exx. */
		if (i!=-1 && i!=R_EAX && i!=R_EBX && i!=R_ECX && i!=R_EDX
		    && i!=R_EBP && i!=R_ESP && i!=R_ESI && i!=R_EDI)
		    return NULL;
		if (b!=-1 && b!=R_EAX && b!=R_EBX && b!=R_ECX && b!=R_EDX
		    && b!=R_EBP && b!=R_ESP && b!=R_ESI && b!=R_EDI)
		    return NULL;

		/* While we're here, ensure the user didn't specify WORD. */
		if (input->addr_size == 16)
		    return NULL;

		/* now reorganise base/index */
		if (b==i)	       /* convert EAX+2*EAX to 3*EAX */
		    b = -1, s++;
		if (b==-1 && s==1)     /* single register should be base */
		    b = i, i = -1;
		if (((s==2 && i!=R_ESP) || s==3 || s==5 || s==9) && b==-1)
		    b = i, s--;       /* convert 3*EAX to EAX+2*EAX */
		if (s==1 && i==R_ESP)  /* swap ESP into base if scale is 1 */
		    i = b, b = R_ESP;
		if (i==R_ESP || (s!=1 && s!=2 && s!=4 && s!=8 && i!=-1))
		    return NULL;      /* wrong, for various reasons */

		if (i==-1 && b!=R_ESP) {/* no SIB needed */
		    int mod, rm;
		    switch(b) {
		      case R_EAX: rm = 0; break;
		      case R_ECX: rm = 1; break;
		      case R_EDX: rm = 2; break;
		      case R_EBX: rm = 3; break;
		      case R_EBP: rm = 5; break;
		      case R_ESI: rm = 6; break;
		      case R_EDI: rm = 7; break;
		      case -1: rm = 5; break;
		      default:	       /* should never happen */
			return NULL;
		    }
		    if (b==-1 || (b!=R_EBP && o==0 &&
				  seg==NO_SEG && !forw_ref))
		    	mod = 0;
		    else if (o>=-128 && o<=127 && seg==NO_SEG && !forw_ref)
		    	mod = 1;
		    else
		    	mod = 2;

		    output->sib_present = FALSE;
		    output->bytes = (b==-1 || mod==2 ? 4 : mod);
		    output->modrm = (mod<<6) | (rfield<<3) | rm;
		} else {	       /* we need a SIB */
		    int mod, scale, index, base;

		    switch (b) {
		      case R_EAX: base = 0; break;
		      case R_ECX: base = 1; break;
		      case R_EDX: base = 2; break;
		      case R_EBX: base = 3; break;
		      case R_ESP: base = 4; break;
		      case R_EBP: case -1: base = 5; break;
		      case R_ESI: base = 6; break;
		      case R_EDI: base = 7; break;
		      default:	       /* then what the smeg is it? */
			return NULL;  /* panic */
		    }

		    switch (i) {
		      case R_EAX: index = 0; break;
		      case R_ECX: index = 1; break;
		      case R_EDX: index = 2; break;
		      case R_EBX: index = 3; break;
		      case -1: index = 4; break;
		      case R_EBP: index = 5; break;
		      case R_ESI: index = 6; break;
		      case R_EDI: index = 7; break;
		      default:	       /* then what the smeg is it? */
			return NULL;  /* panic */
		    }

		    if (i==-1) s = 1;
		    switch (s) {
		      case 1: scale = 0; break;
		      case 2: scale = 1; break;
		      case 4: scale = 2; break;
		      case 8: scale = 3; break;
		      default:	       /* then what the smeg is it? */
			return NULL;  /* panic */
		    }

		    if (b==-1 || (b!=R_EBP && o==0 &&
				  seg==NO_SEG && !forw_ref))
		    	mod = 0;
		    else if (o>=-128 && o<=127 && seg==NO_SEG && !forw_ref)
		    	mod = 1;
		    else
		    	mod = 2;

		    output->sib_present = TRUE;
		    output->bytes = (b==-1 || mod==2 ? 4 : mod);
		    output->modrm = (mod<<6) | (rfield<<3) | 4;
		    output->sib = (scale<<6) | (index<<3) | base;
		}
	    } else {		       /* it's 16-bit */
		int mod, rm;

		/* check all registers are BX, BP, SI or DI */
		if ((b!=-1 && b!=R_BP && b!=R_BX && b!=R_SI && b!=R_DI) ||
		    (i!=-1 && i!=R_BP && i!=R_BX && i!=R_SI && i!=R_DI))
		    return NULL;

		/* ensure the user didn't specify DWORD */
		if (input->addr_size == 32)
		    return NULL;

		if (s!=1 && i!=-1) return NULL;/* no can do, in 16-bit EA */
		if (b==-1 && i!=-1) b ^= i ^= b ^= i;   /* swap them round */
		if ((b==R_SI || b==R_DI) && i!=-1)
		    b ^= i ^= b ^= i; /* have BX/BP as base, SI/DI index */
		if (b==i) return NULL;/* shouldn't ever happen, in theory */
		if (i!=-1 && b!=-1 &&
		    (i==R_BP || i==R_BX || b==R_SI || b==R_DI))
		    return NULL;      /* invalid combinations */
		if (b==-1)	       /* pure offset: handled above */
		    return NULL;      /* so if it gets to here, panic! */

		rm = -1;
		if (i!=-1)
		    switch (i*256 + b) {
		      case R_SI*256+R_BX: rm=0; break;
		      case R_DI*256+R_BX: rm=1; break;
		      case R_SI*256+R_BP: rm=2; break;
		      case R_DI*256+R_BP: rm=3; break;
		    }
		else
		    switch (b) {
		      case R_SI: rm=4; break;
		      case R_DI: rm=5; break;
		      case R_BP: rm=6; break;
		      case R_BX: rm=7; break;
		    }
		if (rm==-1)	       /* can't happen, in theory */
		    return NULL;      /* so panic if it does */

		if (o==0 && seg==NO_SEG && !forw_ref && rm!=6)
		    mod = 0;
		else if (o>=-128 && o<=127 && seg==NO_SEG && !forw_ref)
		    mod = 1;
		else
		    mod = 2;

		output->sib_present = FALSE;  /* no SIB - it's 16-bit */
		output->bytes = mod;  /* bytes of offset needed */
		output->modrm = (mod<<6) | (rfield<<3) | rm;
	    }
	}
    }
    output->size = 1 + output->sib_present + output->bytes;
    return output;
}

static int chsize (operand *input, int addrbits) {
    if (!(MEMORY & ~input->type)) {
	int i=input->indexreg, b=input->basereg;

	if (input->scale==0) i = -1;

	if (i == -1 && b == -1) /* pure offset */
	    return (input->addr_size != 0 && input->addr_size != addrbits);

	if (i==R_EAX || i==R_EBX || i==R_ECX || i==R_EDX
	    || i==R_EBP || i==R_ESP || i==R_ESI || i==R_EDI
	    || b==R_EAX || b==R_EBX || b==R_ECX || b==R_EDX
	    || b==R_EBP || b==R_ESP || b==R_ESI || b==R_EDI)
	    return (addrbits==16);
	else
	    return (addrbits==32);
    } else
    	return 0;
}