#!/usr/bin/perl
#
# insns.pl   produce insnsa.c, insnsd.c, insnsi.h, insnsn.c from insns.dat
#
# The Netwide Assembler is copyright (C) 1996 Simon Tatham and
# Julian Hall. All rights reserved. The software is
# redistributable under the license given in the file "LICENSE"
# distributed in the NASM archive.

# Opcode prefixes which need their own opcode tables
# LONGER PREFIXES FIRST!
@disasm_prefixes = qw(0F24 0F25 0F38 0F3A 0F7A 0FA6 0FA7 0F);

# This should match MAX_OPERANDS from nasm.h
$MAX_OPERANDS = 5;

# Add VEX/XOP prefixes
@vex_class = ( 'vex', 'xop' );
$vex_classes = scalar(@vex_class);
@vexlist = ();
%vexmap = ();
for ($c = 0; $c < $vex_classes; $c++) {
    $vexmap{$vex_class[$c]} = $c;
    for ($m = 0; $m < 32; $m++) {
	for ($lp = 0; $lp < 8; $lp++) {
	    push(@vexlist, sprintf("%s%02X%01X", $vex_class[$c], $m, $lp));
	}
    }
}
@disasm_prefixes = (@vexlist, @disasm_prefixes);

@bytecode_count = (0) x 256;

print STDERR "Reading insns.dat...\n";

@args   = ();
undef $output;
foreach $arg ( @ARGV ) {
    if ( $arg =~ /^\-/ ) {
	if  ( $arg =~ /^\-([abdin])$/ ) {
	    $output = $1;
	} else {
	    die "$0: Unknown option: ${arg}\n";
	}
    } else {
	push (@args, $arg);
    }
}

$fname = "insns.dat" unless $fname = $args[0];
open (F, $fname) || die "unable to open $fname";

%dinstables = ();
@bytecode_list = ();

$line = 0;
$insns = 0;
while (<F>) {
  $line++;
  chomp;
  next if ( /^\s*(\;.*|)$/ );   # comments or blank lines

  unless (/^\s*(\S+)\s+(\S+)\s+(\S+|\[.*\])\s+(\S+)\s*$/) {
      warn "line $line does not contain four fields\n";
      next;
  }
  @fields = ($1, $2, $3, $4);
  @field_list = ([@fields, 0]);

  if ($fields[1] =~ /\*/) {
      # This instruction has relaxed form(s)
      if ($fields[2] !~ /^\[/) {
	  warn "line $line has an * operand but uses raw bytecodes\n";
	  next;
      }
      
      $opmask = 0;
      @ops = split(/,/, $fields[1]);
      for ($oi = 0; $oi < scalar @ops; $oi++) {
	  if ($ops[$oi] =~ /\*$/) {
	      if ($oi == 0) {
		  warn "line $line has a first operand with a *\n";
		  next;
	      }
	      $opmask |= 1 << $oi;
	  }
      }

      for ($oi = 1; $oi < (1 << scalar @ops); $oi++) {
	  if (($oi & ~$opmask) == 0) {
	      my @xops = ();
	      my $omask = ~$oi;
	      for ($oj = 0; $oj < scalar(@ops); $oj++) {
		  if ($omask & 1) {
		      push(@xops, $ops[$oj]);
		  }
		  $omask >>= 1;
	      }
	      push(@field_list, [$fields[0], join(',', @xops),
				 $fields[2], $fields[3], $oi]);
	  }
      }
  }

  foreach $fptr (@field_list) {
      @fields = @$fptr;
      ($formatted, $nd) = format_insn(@fields);
      if ($formatted) {
	  $insns++;
	  $aname = "aa_$fields[0]";
	  push @$aname, $formatted;
      }
      if ( $fields[0] =~ /cc$/ ) {
	  # Conditional instruction
	  $k_opcodes_cc{$fields[0]}++;
      } else {
	  # Unconditional instruction
	  $k_opcodes{$fields[0]}++;
      }
      if ($formatted && !$nd) {
	  push @big, $formatted;
	  my @sseq = startseq($fields[2], $fields[4]);
	  foreach $i (@sseq) {
	      if (!defined($dinstables{$i})) {
		  $dinstables{$i} = [];
	      }
	      push(@{$dinstables{$i}}, $#big);
	  }
      }
  }
}

close F;

#
# Generate the bytecode array.  At this point, @bytecode_list contains
# the full set of bytecodes.
#

# Sort by descending length
@bytecode_list = sort { scalar(@$b) <=> scalar(@$a) } @bytecode_list;
@bytecode_array = ();
%bytecode_pos = ();
$bytecode_next = 0;
foreach $bl (@bytecode_list) {
    my $h = hexstr(@$bl);
    next if (defined($bytecode_pos{$h}));

    push(@bytecode_array, $bl);
    while ($h ne '') {
	$bytecode_pos{$h} = $bytecode_next;
	$h = substr($h, 2);
	$bytecode_next++;
    }
}
undef @bytecode_list;

@opcodes    = sort keys(%k_opcodes);
@opcodes_cc = sort keys(%k_opcodes_cc);

if ( !defined($output) || $output eq 'b') {
    print STDERR "Writing insnsb.c...\n";

    open B, ">insnsb.c";

    print B "/* This file auto-generated from insns.dat by insns.pl" .
        " - don't edit it */\n\n";

    print B "#include \"nasm.h\"\n";
    print B "#include \"insns.h\"\n\n";

    print B "const uint8_t nasm_bytecodes[$bytecode_next] = {\n";

    $p = 0;
    foreach $bl (@bytecode_array) {
	printf B "    /* %5d */ ", $p;
	foreach $d (@$bl) {
	    printf B "%#o,", $d;
	    $p++;
	}
	printf B "\n";
    }
    print B "};\n";

    print B "\n";
    print B "/*\n";
    print B " * Bytecode frequencies (including reuse):\n";
    print B " *\n";
    for ($i = 0; $i < 32; $i++) {
	print B " *";
	for ($j = 0; $j < 256; $j += 32) {
	    print B " |" if ($j);
	    printf B " %3o:%4d", $i+$j, $bytecode_count[$i+$j];
	}
	print B "\n";
    }
    print B " */\n";

    close B;
}

if ( !defined($output) || $output eq 'a' ) {
    print STDERR "Writing insnsa.c...\n";

    open A, ">insnsa.c";

    print A "/* This file auto-generated from insns.dat by insns.pl" .
        " - don't edit it */\n\n";

    print A "#include \"nasm.h\"\n";
    print A "#include \"insns.h\"\n\n";

    foreach $i (@opcodes, @opcodes_cc) {
	print A "static const struct itemplate instrux_${i}[] = {\n";
	$aname = "aa_$i";
	foreach $j (@$aname) {
	    print A "    ", codesubst($j), "\n";
	}
	print A "    ITEMPLATE_END\n};\n\n";
    }
    print A "const struct itemplate * const nasm_instructions[] = {\n";
    foreach $i (@opcodes, @opcodes_cc) {
	print A "    instrux_${i},\n";
    }
    print A "};\n";

    close A;
}

if ( !defined($output) || $output eq 'd' ) {
    print STDERR "Writing insnsd.c...\n";

    open D, ">insnsd.c";

    print D "/* This file auto-generated from insns.dat by insns.pl" .
        " - don't edit it */\n\n";

    print D "#include \"nasm.h\"\n";
    print D "#include \"insns.h\"\n\n";

    print D "static const struct itemplate instrux[] = {\n";
    $n = 0;
    foreach $j (@big) {
	printf D "    /* %4d */ %s\n", $n++, codesubst($j);
    }
    print D "};\n";

    foreach $h (sort(keys(%dinstables))) {
	next if ($h eq '');	# Skip pseudo-instructions
	print D "\nstatic const struct itemplate * const itable_${h}[] = {\n";
	foreach $j (@{$dinstables{$h}}) {
	    print D "    instrux + $j,\n";
	}
	print D "};\n";
    }

    @prefix_list = ();
    foreach $h (@disasm_prefixes, '') {
	for ($c = 0; $c < 256; $c++) {
	    $nn = sprintf("%s%02X", $h, $c);
	    if ($is_prefix{$nn} || defined($dinstables{$nn})) {
		# At least one entry in this prefix table
		push(@prefix_list, $h);
		$is_prefix{$h} = 1;
		last;
	    }
	}
    }

    foreach $h (@prefix_list) {
	print D "\n";
	print D "static " unless ($h eq '');
	print D "const struct disasm_index ";
	print D ($h eq '') ? 'itable' : "itable_$h";
	print D "[256] = {\n";
	for ($c = 0; $c < 256; $c++) {
	    $nn = sprintf("%s%02X", $h, $c);
	    if ($is_prefix{$nn}) {
		die "$fname: ambiguous decoding of $nn\n"
		    if (defined($dinstables{$nn}));
		printf D "    { itable_%s, -1 },\n", $nn;
	    } elsif (defined($dinstables{$nn})) {
		printf D "    { itable_%s, %u },\n",
		$nn, scalar(@{$dinstables{$nn}});
	    } else {
		printf D "    { NULL, 0 },\n";
	    }
	}
	print D "};\n";
    }

    printf D "\nconst struct disasm_index * const itable_vex[%d][32][8] =\n",
        $vex_classes;
    print D "{\n";
    for ($c = 0; $c < $vex_classes; $c++) {
	print D "    {\n";
	for ($m = 0; $m < 32; $m++) {
	    print D "        {\n";
	    for ($lp = 0; $lp < 8; $lp++) {
		$vp = sprintf("%s%02X%01X", $vex_class[$c], $m, $lp);
		if ($is_prefix{$vp}) {
		    printf D "            itable_%s,\n", $vp;
		} else {
		    print  D "            NULL,\n";
		}
	    }
	    print D "        },\n";
	}
	print D "    },\n";
    }
    print D "};\n";

    close D;
}

if ( !defined($output) || $output eq 'i' ) {
    print STDERR "Writing insnsi.h...\n";

    open I, ">insnsi.h";

    print I "/* This file is auto-generated from insns.dat by insns.pl" .
        " - don't edit it */\n\n";
    print I "/* This file in included by nasm.h */\n\n";

    print I "/* Instruction names */\n\n";
    print I "#ifndef NASM_INSNSI_H\n";
    print I "#define NASM_INSNSI_H 1\n\n";
    print I "enum opcode {\n";
    $maxlen = 0;
    foreach $i (@opcodes, @opcodes_cc) {
	print I "\tI_${i},\n";
	$len = length($i);
	$len++ if ( $i =~ /cc$/ ); # Condition codes can be 3 characters long
	$maxlen = $len if ( $len > $maxlen );
    }
    print I "\tI_none = -1\n";
    print I "\n};\n\n";
    print I "#define MAX_INSLEN ", $maxlen, "\n";
    print I "#define FIRST_COND_OPCODE I_", $opcodes_cc[0], "\n\n";
    print I "#endif /* NASM_INSNSI_H */\n";

    close I;
}

if ( !defined($output) || $output eq 'n' ) {
    print STDERR "Writing insnsn.c...\n";

    open N, ">insnsn.c";

    print N "/* This file is auto-generated from insns.dat by insns.pl" .
        " - don't edit it */\n\n";
    print N "#include \"tables.h\"\n\n";

    print N "const char * const nasm_insn_names[] = {";
    $first = 1;
    foreach $i (@opcodes, @opcodes_cc) {
	print N "," if ( !$first );
	$first = 0;
	$ilower = $i;
	$ilower =~ s/cc$//;	# Remove conditional cc suffix
	$ilower =~ tr/A-Z/a-z/;	# Change to lower case (Perl 4 compatible)
	print N "\n\t\"${ilower}\"";
    }
    print N "\n};\n";
    close N;
}

printf STDERR "Done: %d instructions\n", $insns;

# Count primary bytecodes, for statistics
sub count_bytecodes(@) {
    my $skip = 0;
    foreach my $bc (@_) {
	if ($skip) {
	    $skip--;
	    next;
	}
	$bytecode_count[$bc]++;
	if ($bc >= 01 && $bc <= 04) {
	    $skip = $bc;
	} elsif (($bc & ~03) == 010) {
	    $skip = 1;
	} elsif (($bc & ~013) == 0144) {
	    $skip = 1;
	} elsif ($bc == 0172) {
	    $skip = 1;
	} elsif ($bc >= 0260 && $bc <= 0270) {
	    $skip = 2;
	} elsif ($bc == 0330) {
	    $skip = 1;
	}
    }
}

sub format_insn($$$$$) {
    my ($opcode, $operands, $codes, $flags, $relax) = @_;
    my $num, $nd = 0;
    my @bytecode;

    return (undef, undef) if $operands eq "ignore";

    # format the operands
    $operands =~ s/\*//g;
    $operands =~ s/:/|colon,/g;
    $operands =~ s/mem(\d+)/mem|bits$1/g;
    $operands =~ s/mem/memory/g;
    $operands =~ s/memory_offs/mem_offs/g;
    $operands =~ s/imm(\d+)/imm|bits$1/g;
    $operands =~ s/imm/immediate/g;
    $operands =~ s/rm(\d+)/rm_gpr|bits$1/g;
    $operands =~ s/(mmx|xmm|ymm)rm/rm_$1/g;
    $operands =~ s/\=([0-9]+)/same_as|$1/g;
    if ($operands eq 'void') {
	@ops = ();
    } else {
	@ops = split(/\,/, $operands);
    }
    $num = scalar(@ops);
    while (scalar(@ops) < $MAX_OPERANDS) {
	push(@ops, '0');
    }
    $operands = join(',', @ops);
    $operands =~ tr/a-z/A-Z/;

    # format the flags
    $flags =~ s/,/|IF_/g;
    $flags =~ s/(\|IF_ND|IF_ND\|)//, $nd = 1 if $flags =~ /IF_ND/;
    $flags = "IF_" . $flags;

    @bytecode = (decodify($codes, $relax), 0);
    push(@bytecode_list, [@bytecode]);
    $codes = hexstr(@bytecode);
    count_bytecodes(@bytecode);

    ("{I_$opcode, $num, {$operands}, \@\@CODES-$codes\@\@, $flags},", $nd);
}

#
# Look for @@CODES-xxx@@ sequences and replace them with the appropriate
# offset into nasm_bytecodes
#
sub codesubst($) {
    my($s) = @_;
    my $n;

    while ($s =~ /\@\@CODES-([0-9A-F]+)\@\@/) {
	my $pos = $bytecode_pos{$1};
	if (!defined($pos)) {
	    die "$fname: no position assigned to byte code $1\n";
	}
	$s = $` . "nasm_bytecodes+${pos}" . "$'";
    }
    return $s;
}

sub addprefix ($@) {
    my ($prefix, @list) = @_;
    my $x;
    my @l = ();

    foreach $x (@list) {
	push(@l, sprintf("%s%02X", $prefix, $x));
    }

    return @l;
}

#
# Turn a code string into a sequence of bytes
#
sub decodify($$) {
  # Although these are C-syntax strings, by convention they should have
  # only octal escapes (for directives) and hexadecimal escapes
  # (for verbatim bytes)
    my($codestr, $relax) = @_;

    if ($codestr =~ /^\s*\[([^\]]*)\]\s*$/) {
	return byte_code_compile($1, $relax);
    }

    my $c = $codestr;
    my @codes = ();

    while ($c ne '') {
	if ($c =~ /^\\x([0-9a-f]+)(.*)$/i) {
	    push(@codes, hex $1);
	    $c = $2;
	    next;
	} elsif ($c =~ /^\\([0-7]{1,3})(.*)$/) {
	    push(@codes, oct $1);
	    $c = $2;
	    next;
	} else {
	    die "$fname: unknown code format in \"$codestr\"\n";
	}
    }

    return @codes;
}

# Turn a numeric list into a hex string
sub hexstr(@) {
    my $s = '';
    my $c;

    foreach $c (@_) {
	$s .= sprintf("%02X", $c);
    }
    return $s;
}

# Here we determine the range of possible starting bytes for a given
# instruction. We need only consider the codes:
# \[1234]      mean literal bytes, of course
# \1[0123]     mean byte plus register value
# \330         means byte plus condition code
# \0 or \340   mean give up and return empty set
# \34[4567]    mean PUSH/POP of segment registers: special case
# \17[234]     skip is4 control byte
# \26x \270    skip VEX control bytes
sub startseq($$) {
  my ($codestr, $relax) = @_;
  my $word, @range;
  my @codes = ();
  my $c = $codestr;
  my $c0, $c1, $i;
  my $prefix = '';

  @codes = decodify($codestr, $relax);

  while ($c0 = shift(@codes)) {
      $c1 = $codes[0];
      if ($c0 >= 01 && $c0 <= 04) {
	  # Fixed byte string
	  my $fbs = $prefix;
	  while (1) {
	      if ($c0 >= 01 && $c0 <= 04) {
		  while ($c0--) {
		      $fbs .= sprintf("%02X", shift(@codes));
		  }
	      } else {
		  last;
	      }
	      $c0 = shift(@codes);
	  }

	  foreach $pfx (@disasm_prefixes) {
	      if (substr($fbs, 0, length($pfx)) eq $pfx) {
		  $prefix = $pfx;
		  $fbs = substr($fbs, length($pfx));
		  last;
	      }
	  }

	  if ($fbs ne '') {
	      return ($prefix.substr($fbs,0,2));
	  }

	  unshift(@codes, $c0);
      } elsif ($c0 >= 010 && $c0 <= 013) {
	  return addprefix($prefix, $c1..($c1+7));
      } elsif (($c0 & ~013) == 0144) {
	  return addprefix($prefix, $c1, $c1|2);
      } elsif ($c0 == 0330) {
	  return addprefix($prefix, $c1..($c1+15));
      } elsif ($c0 == 0 || $c0 == 0340) {
	  return $prefix;
      } elsif ($c0 == 0344) {
	  return addprefix($prefix, 0x06, 0x0E, 0x16, 0x1E);
      } elsif ($c0 == 0345) {
	  return addprefix($prefix, 0x07, 0x17, 0x1F);
      } elsif ($c0 == 0346) {
	  return addprefix($prefix, 0xA0, 0xA8);
      } elsif ($c0 == 0347) {
	  return addprefix($prefix, 0xA1, 0xA9);
      } elsif (($c0 & ~3) == 0260 || $c0 == 0270) {
	  my $c,$m,$wlp;
	  $m   = shift(@codes);
	  $wlp = shift(@codes);
	  $c = ($m >> 6);
	  $m = $m & 31;
	  $prefix .= sprintf('%s%02X%01X', $vex_class[$c], $m, $wlp & 7);
      } elsif ($c0 >= 0172 && $c0 <= 174) {
	  shift(@codes);	# Skip is4 control byte
      } else {
	  # We really need to be able to distinguish "forbidden"
	  # and "ignorable" codes here
      }
  }
  return $prefix;
}

#
# This function takes a series of byte codes in a format which is more
# typical of the Intel documentation, and encode it.
#
# The format looks like:
#
# [operands: opcodes]
#
# The operands word lists the order of the operands:
#
# r = register field in the modr/m
# m = modr/m
# v = VEX "v" field
# d = DREX "dst" field
# i = immediate
# s = register field of is4/imz2 field
# - = implicit (unencoded) operand
#
# For an operand that should be filled into more than one field,
# enter it as e.g. "r+v".
#
sub byte_code_compile($$) {
    my($str, $relax) = @_;
    my $opr;
    my $opc;
    my @codes = ();
    my $litix = undef;
    my %oppos = ();
    my $i;
    my $op, $oq;
    my $opex;

    unless ($str =~ /^(([^\s:]*)\:|)\s*(.*\S)\s*$/) {
	die "$fname: $line: cannot parse: [$str]\n";
    }
    $opr = "\L$2";
    $opc = "\L$3";

    my $op = 0;
    for ($i = 0; $i < length($opr); $i++) {
	my $c = substr($opr,$i,1);
	if ($c eq '+') {
	    $op--;
	} else {
	    if ($relax & 1) {
		$op--;
	    }
	    $relax >>= 1;
	    $oppos{$c} = $op++;
	}
    }

    $prefix_ok = 1;
    foreach $op (split(/\s*(?:\s|(?=[\/\\]))/, $opc)) {
	if ($op eq 'o16') {
	    push(@codes, 0320);
	} elsif ($op eq 'o32') {
	    push(@codes, 0321);
	} elsif ($op eq 'o64') {  # 64-bit operand size requiring REX.W
	    push(@codes, 0324);
	} elsif ($op eq 'o64nw') { # Implied 64-bit operand size (no REX.W)
	    push(@codes, 0323);
	} elsif ($op eq 'a16') {
	    push(@codes, 0310);
	} elsif ($op eq 'a32') {
	    push(@codes, 0311);
	} elsif ($op eq 'a64') {
	    push(@codes, 0313);
	} elsif ($op eq '!osp') {
	    push(@codes, 0364);
	} elsif ($op eq '!asp') {
	    push(@codes, 0365);
	} elsif ($op eq 'rex.l') {
	    push(@codes, 0334);
	} elsif ($op eq 'repe') {
	    push(@codes, 0335);
	} elsif ($prefix_ok && $op =~ /^(66|f2|f3|np)$/) {
	    # 66/F2/F3 prefix used as an opcode extension, or np = no prefix
	    if ($op eq '66') {
		push(@codes, 0361);
	    } elsif ($op eq 'f2') {
		push(@codes, 0362);
	    } elsif ($op eq 'f3') {
		push(@codes, 0363);
	    } else {
		push(@codes, 0360);
	    }
	} elsif ($op =~ /^[0-9a-f]{2}$/) {
	    if (defined($litix) && $litix+$codes[$litix]+1 == scalar @codes &&
		$codes[$litix] < 4) {
		$codes[$litix]++;
		push(@codes, hex $op);
	    } else {
		$litix = scalar(@codes);
		push(@codes, 01, hex $op);
	    }
	    $prefix_ok = 0;
	} elsif ($op eq '/r') {
	    if (!defined($oppos{'r'}) || !defined($oppos{'m'})) {
		die "$fname: $line: $op requires r and m operands\n";
	    }
	    $opex = (($oppos{'m'} & 4) ? 06 : 0) |
		    (($oppos{'r'} & 4) ? 05 : 0);
	    push(@codes, $opex) if ($opex);
	    push(@codes, 0100 + (($oppos{'m'} & 3) << 3) + ($oppos{'r'} & 3));
	    $prefix_ok = 0;
	} elsif ($op =~ m:^/([0-7])$:) {
	    if (!defined($oppos{'m'})) {
		die "$fname: $line: $op requires m operand\n";
	    }
	    push(@codes, 06) if ($oppos{'m'} & 4);
	    push(@codes, 0200 + (($oppos{'m'} & 3) << 3) + $1);
	    $prefix_ok = 0;
	} elsif ($op =~ /^(vex|xop)(|\..*)$/) {
	    my $c = $vexmap{$1};
	    my ($m,$w,$l,$p) = (undef,2,undef,0);
	    my $has_nds = 0;
	    my @subops = split(/\./, $op);
	    shift @subops;	# Drop prefix
	    foreach $oq (@subops) {
		if ($oq eq '128' || $oq eq 'l0') {
		    $l = 0;
		} elsif ($oq eq '256' || $oq eq 'l1') {
		    $l = 1;
		} elsif ($oq eq 'w0') {
		    $w = 0;
		} elsif ($oq eq 'w1') {
		    $w = 1;
		} elsif ($oq eq 'wx') {
		    $w = 2;
		} elsif ($oq eq 'ww') {
		    $w = 3;
		} elsif ($oq eq 'p0') {
		    $p = 0;
		} elsif ($oq eq '66' || $oq eq 'p1') {
		    $p = 1;
		} elsif ($oq eq 'f3' || $oq eq 'p2') {
		    $p = 2;
		} elsif ($oq eq 'f2' || $oq eq 'p3') {
		    $p = 3;
		} elsif ($oq eq '0f') {
		    $m = 1;
		} elsif ($oq eq '0f38') {
		    $m = 2;
		} elsif ($oq eq '0f3a') {
		    $m = 3;
		} elsif ($oq =~ /^m([0-9]+)$/) {
		    $m = $1+0;
		} elsif ($oq eq 'nds' || $oq eq 'ndd' || $oq eq 'dds') {
		    if (!defined($oppos{'v'})) {
			die "$fname: $line: vex.$oq without 'v' operand\n";
		    }
		    $has_nds = 1;
		} else {
		    die "$fname: $line: undefined VEX subcode: $oq\n";
		}
	    }
	    if (!defined($m) || !defined($w) || !defined($l) || !defined($p)) {
		die "$fname: $line: missing fields in VEX specification\n";
	    }
	    if (defined($oppos{'v'}) && !$has_nds) {
		die "$fname: $line: 'v' operand without vex.nds or vex.ndd\n";
	    }
	    push(@codes, defined($oppos{'v'}) ? 0260+($oppos{'v'} & 3) : 0270,
		 ($c << 6)+$m, ($w << 3)+($l << 2)+$p);
	    $prefix_ok = 0;
	} elsif ($op =~ /^\/drex([01])$/) {
	    my $oc0 = $1;
	    if (!defined($oppos{'d'})) {
		die "$fname: $line: DREX without a 'd' operand\n";
	    }
	    # Note the use of *unshift* here, as opposed to *push*.
	    # This is because NASM want this byte code at the start of
	    # the instruction sequence, but the AMD documentation puts
	    # this at (roughly) the position of the drex byte itself.
	    # This allows us to match the AMD documentation and still
	    # do the right thing.
	    unshift(@codes, 0160+($oppos{'d'} & 3)+($oc0 ? 4 : 0));
	    unshift(@codes, 05) if ($oppos{'d'} & 4);
	} elsif ($op =~ /^(ib\,s|ib|ibx|ib\,w|iw|iwd|id|idx|iwdq|rel|rel8|rel16|rel32|iq|seg|ibw|ibd|ibd,s)$/) {
	    if (!defined($oppos{'i'})) {
		die "$fname: $line: $op without 'i' operand\n";
	    }
	    if ($op eq 'ib,s') { # Signed imm8
		push(@codes, 05) if ($oppos{'i'} & 4);
		push(@codes, 014+($oppos{'i'} & 3));
	    } elsif ($op eq 'ib') { # imm8
		push(@codes, 05) if ($oppos{'i'} & 4);
		push(@codes, 020+($oppos{'i'} & 3));
	    } elsif ($op eq 'ib,u') { # Unsigned imm8
		push(@codes, 05) if ($oppos{'i'} & 4);
		push(@codes, 024+($oppos{'i'} & 3));
	    } elsif ($op eq 'iw') { # imm16
		push(@codes, 05) if ($oppos{'i'} & 4);
		push(@codes, 030+($oppos{'i'} & 3));
	    } elsif ($op eq 'ibx') { # imm8 sign-extended to opsize
		push(@codes, 05) if ($oppos{'i'} & 4);
		push(@codes, 0274+($oppos{'i'} & 3));
	    } elsif ($op eq 'iwd') { # imm16 or imm32, depending on opsize
		push(@codes, 05) if ($oppos{'i'} & 4);
		push(@codes, 034+($oppos{'i'} & 3));
	    } elsif ($op eq 'id') { # imm32
		push(@codes, 05) if ($oppos{'i'} & 4);
		push(@codes, 040+($oppos{'i'} & 3));
	    } elsif ($op eq 'idx') { # imm32 extended to 64 bits
		push(@codes, 05) if ($oppos{'i'} & 4);
		push(@codes, 0254+($oppos{'i'} & 3));
	    } elsif ($op eq 'iwdq') { # imm16/32/64, depending on opsize
		push(@codes, 05) if ($oppos{'i'} & 4);
		push(@codes, 044+($oppos{'i'} & 3));
	    } elsif ($op eq 'rel8') {
		push(@codes, 05) if ($oppos{'i'} & 4);
		push(@codes, 050+($oppos{'i'} & 3));
	    } elsif ($op eq 'iq') {
		push(@codes, 05) if ($oppos{'i'} & 4);
		push(@codes, 054+($oppos{'i'} & 3));
	    } elsif ($op eq 'rel16') {
		push(@codes, 05) if ($oppos{'i'} & 4);
		push(@codes, 060+($oppos{'i'} & 3));
	    } elsif ($op eq 'rel') { # 16 or 32 bit relative operand
		push(@codes, 05) if ($oppos{'i'} & 4);
		push(@codes, 064+($oppos{'i'} & 3));
	    } elsif ($op eq 'rel32') {
		push(@codes, 05) if ($oppos{'i'} & 4);
		push(@codes, 070+($oppos{'i'} & 3));
	    } elsif ($op eq 'seg') {
		push(@codes, 05) if ($oppos{'i'} & 4);
		push(@codes, 074+($oppos{'i'} & 3));
	    } elsif ($op eq 'ibw') { # imm16 that can be bytified
		if (!defined($s_pos)) {
		    die "$fname: $line: $op without a +s byte\n";
		}
		$codes[$s_pos] += 0144;
		push(@codes, 05) if ($oppos{'i'} & 4);
		push(@codes, 0140+($oppos{'i'} & 3));
	    } elsif ($op eq 'ibd') { # imm32 that can be bytified
		if (!defined($s_pos)) {
		    die "$fname: $line: $op without a +s byte\n";
		}
		$codes[$s_pos] += 0154;
		push(@codes, 05) if ($oppos{'i'} & 4);
		push(@codes, 0150+($oppos{'i'} & 3));
	    } elsif ($op eq 'ibd,s') {
		# imm32 that can be bytified, sign extended to 64 bits
		if (!defined($s_pos)) {
		    die "$fname: $line: $op without a +s byte\n";
		}
		$codes[$s_pos] += 0154;
		push(@codes, 05) if ($oppos{'i'} & 4);
		push(@codes, 0250+($oppos{'i'} & 3));
	    }
	    $prefix_ok = 0;
	} elsif ($op eq '/is4') {
	    if (!defined($oppos{'s'})) {
		die "$fname: $line: $op without 's' operand\n";
	    }
	    if (defined($oppos{'i'})) {
		push(@codes, 0172, ($oppos{'s'} << 3)+$oppos{'i'});
	    } else {
		push(@codes, 0174, $oppos{'s'});
	    }
	    $prefix_ok = 0;
	} elsif ($op =~ /^\/is4\=([0-9]+)$/) {
	    my $imm = $1;
	    if (!defined($oppos{'s'})) {
		die "$fname: $line: $op without 's' operand\n";
	    }
	    if ($imm < 0 || $imm > 15) {
		die "$fname: $line: invalid imm4 value for $op: $imm\n";
	    }
	    push(@codes, 0173, ($oppos{'s'} << 4) + $imm);
	    $prefix_ok = 0;
	} elsif ($op =~ /^([0-9a-f]{2})\+s$/) {
	    if (!defined($oppos{'i'})) {
		die "$fname: $line: $op without 'i' operand\n";
	    }
	    $s_pos = scalar @codes;
	    push(@codes, 05) if ($oppos{'i'} & 4);
	    push(@codes, $oppos{'i'} & 3, hex $1);
	    $prefix_ok = 0;
	} elsif ($op =~ /^([0-9a-f]{2})\+c$/) {
	    push(@codes, 0330, hex $1);
	    $prefix_ok = 0;
	} elsif ($op =~ /^\\([0-7]+|x[0-9a-f]{2})$/) {
	    # Escape to enter literal bytecodes
	    push(@codes, oct $1);
	} else {
	    die "$fname: $line: unknown operation: $op\n";
	}
    }

    return @codes;
}