#!/usr/bin/awk -f
BEGIN {
  if (!of) of="lst"
  pos=0
  errors=0
  x86=1
  x80=0
  z80=0
  # lookup table for ord()
  for (i = 32; i <= 128; i++) {
    t=sprintf("%c", i)
    _ord_[t]=i
  }
  # 8-bit general purpose registers
  r8["al"]=0
  r8["cl"]=1
  r8["dl"]=2
  r8["bl"]=3
  r8["ah"]=4
  r8["ch"]=5
  r8["dh"]=6
  r8["bh"]=7
  # 16-bit general purpose registers
  r16["ax"]=0
  r16["cx"]=1
  r16["dx"]=2
  r16["bx"]=3
  r16["sp"]=4
  r16["bp"]=5
  r16["si"]=6
  r16["di"]=7
  # segment registers
  sreg["es"]=0
  sreg["cs"]=1
  sreg["ss"]=2
  sreg["ds"]=3
  # indirect access register combinations
  modstr["bxsi"]=0
  modstr["sibx"]=0
  modstr["bxdi"]=1
  modstr["dibx"]=1
  modstr["bpsi"]=2
  modstr["sibp"]=2
  modstr["bpdi"]=3
  modstr["dibp"]=3
  modstr["si"]=4
  modstr["di"]=5
  modstr["bx"]=7
  # ALU operations
  alu["add"]=0
  alu["or"]=1
  alu["adc"]=2
  alu["sbb"]=3
  alu["and"]=4
  alu["sub"]=5
  alu["xor"]=6
  alu["cmp"]=7
  # near conditional jumps
  ops_rel8["jo"]=112+0
  ops_rel8["jno"]=112+1
  ops_rel8["jb"]=112+2
  ops_rel8["jc"]=112+2
  ops_rel8["jnae"]=112+2
  ops_rel8["jae"]=112+3
  ops_rel8["jnb"]=112+3
  ops_rel8["jnc"]=112+3
  ops_rel8["je"]=112+4
  ops_rel8["jz"]=112+4
  ops_rel8["jne"]=112+5
  ops_rel8["jnz"]=112+5
  ops_rel8["jbe"]=112+6
  ops_rel8["jna"]=112+6
  ops_rel8["ja"]=112+7
  ops_rel8["jnbe"]=112+7
  ops_rel8["js"]=112+8
  ops_rel8["jns"]=112+9
  ops_rel8["jp"]=112+10
  ops_rel8["jpe"]=112+10
  ops_rel8["jnp"]=112+11
  ops_rel8["jpo"]=112+11
  ops_rel8["jl"]=112+12
  ops_rel8["jnge"]=112+12
  ops_rel8["jge"]=112+13
  ops_rel8["jbl"]=112+13
  ops_rel8["jle"]=112+14
  ops_rel8["jng"]=112+14
  ops_rel8["jg"]=112+15
  ops_rel8["jnle"]=112+15
  # single-byte opcodes without operands
  ops_sb["stosb"]=170
  ops_sb["stosw"]=171
  ops_sb["lodsb"]=172
  ops_sb["lodsw"]=173
  ops_sb["ret"]=195
  ops_sb["retf"]=203
}
# error string to insert into listing
function err(str) {
  errors++
  if (of=="lst") printf("**** %s:\n", str)
}
# submit a assembling result to output
# set label of current line to off
function submit(off) {
  if (of=="lst") printf("%04X %-18s %s\n", off, hex, $0)
  if (of=="hex" && hex) printf("%s", hex)
  if (label) {
    if (of=="sym") printf("%s\tsym\t%d\n", label, off)
    if (label in prevsym && prevsym[label]!=off) {
      err(label " different during second pass")
    }
    sym[label]=off
  }
  pos=pos+length(hex)/2
  hex=""
}
# gets a symbol's values
function getsym(name) {
  if (substr(name,1,1)=="0" || int(name)) {
    return int(name)
  }
  if (substr(name,1,1)==".") name = plabel name
  if (name in prevsym) {
    return prevsym[name]
  } else if (name in sym) {
    return sym[name]
  }
  return 0
}
function pushb(val) {
  while (val<0) val=val+256
  hex=hex sprintf("%02X",val)
}
function pushw(val) {
  while (val<0) val=val+65536
  t=sprintf("%04X",val)
  hex=hex substr(t,3) substr(t,1,2)
}
function modrm(str, spare, rs) {
  mod=3
  rm=0
  if (str in rs) {
    mod=3
    rm=rs[str]
  } else if (substr(str,1,1)=="[") {
    rmap=""
    gsub(/^\[|\]$/, "", str)
    split(str,rmp,"+")
    disp=0
    for (i in rmp) {
      if (rmp[i] in r16) {
        rmap=rmap rmp[i]
      } else {
        disp = disp + getsym(rmp[i])
        mod=2
      }
    }
    if (!rmap) {
      mod=0
      rm=6
    } else if (rmap in modstr) {
      rm=modstr[rmap]
    } else {
      err("Bad modR/M")
    }
  }
  #print("modR/M:", mod, spare, rm)
  pushb(mod*64+spare*8+rm)
  if (mod == 1) {
    pushb(disp)
  } else if (mod == 2 || (mod == 0 && rm=6)) {
    pushw(disp)
  }

}
# dont process empty lines or comment lines
/^( |\t)*(;|%)/ || /^( |\t)*$/ {
  if (of=="lst") printf("%24s%s\n","",$0)
  next
}
# load symbols from previous pass
$2=="sym" {
  prevsym[$1]=int($3)
  #printf("; %s (%s=%X)\n", $0,$1,prevsym[$1])
  next
}
# Start parsing the line
# and set up per-line vars
{
  label=$1
  gsub(/:$/, "",label)
  opn=2
  split("", b, ":")
  byteop=1
  wordop=1
  dwordop=1
}
# no label on line! fixup
/^ / || /^\t/ {
  label=""
  opn=1
}
{
  # implement local labels
  if (substr(label,1,1)==".") {
    label=plabel label
  } else if (label) {
    plabel=label
  }
  # take note if we got a instruction size specifier
  op=$(opn)
  if($(opn+1)=="byte") {
    wordop=0
    dwordop=0
    opn++
  } else if ($(opn+1)=="word") {
    byteop=0
    dwordop=0
    opn++
  } else if ($(opn+1)=="dword") {
    byteop=0
    wordop=0
    opn++
  }
  split("", a, ":")
  c=0
  for (i=opn+1;i<=NF;i++) {
    if (substr($(i),1,1)==";") break
    a[++c]=$(i)
    if (substr($(i),1,1)=="\"") {
      do {
        i++
        j=index($(i), "\"")
        if (j) {
          a[c]=a[c] " " substr($(i), 1, j)
          break
        } else {
          a[c]=a[c] " " $(i)
        }
      } while($(i))
    } else {
      gsub(/,$/, "", a[c])
    }
  }
  op1=a[1]
  op2=a[2]
  rm1=(op1 in r16) || (op1 in r8) || substr(op1,1,1)=="["
  rm2=(op2 in r16) || (op2 in r8) || substr(op2,1,1)=="["
}
# the source line is parsed by here:
#   - op: opcode name
#   - a: array of operands, starting with 1
#   - c: number of operands
#   - byteop, wordop, dwordop: test before encoding, all 1 per default
# pseudo-opcodes
op=="cpu" {
  x86=(a[1]=="8088"||a[1]=="8086")
  x80=(a[1]=="8080"||a[1]=="z80")
  z80=(a[1]=="z80")
  submit(pos);next
}
op=="org" {
  pos=getsym(a[1])
  submit(pos);next
}
op=="equ" {
  val=getsym(a[1])
  submit(val);next
}
op=="db" {
  for(i=1;i<=c;i++) {
    if (substr(a[i],1,1)=="\"") {
      for(j=2;j<length(a[i]);j++) {
        pushb(_ord_[substr(a[i],j,1)])
      }
    } else pushb(getsym(a[i]))
  }
}
op=="dw" {
  for(i=1;i<=c;i++) pushw(getsym(a[i]))
}
# x86 opcodes, ordered by my favourite first
# arithmetics: ADD, SUB, XOR etc
x86 && op in alu {
  # modrm <- reg
  if (rm1 && op2 in r8) {
    pushb(0+alu[op]*8)
    modrm(op1, r8[op2], r8)
  } else if (rm1 && op2 in r16) {
    pushb(1+alu[op]*8)
    modrm(op1, r16[op2], r16)
  # reg <- modrm
  } else if (op1 in r8 && rm2) {
    pushb(2+alu[op]*8)
    modrm(op2, r8[op1], r8)
  } else if (op1 in r16 && rm2) {
    pushb(3+alu[op]*8)
    modrm(op2, r16[op1], r16)
  # modrm <- imm
  } else if (byteop && rm1 || op1 in r8) {
    pushb(128) # 80
    modrm(op1, alu[op], r8)
    pushb(getsym(op2))
  } else if (wordop && rm1 || op1 in r16) {
    pushb(129) # 81
    modrm(op1, alu[op], r16)
    pushw(getsym(op2))
  }
}
# MOV variants
x86 && op=="mov" {
  # modrm <-> reg
  if (rm1 && op2 in r8) {
    pushb(136) # 88
    modrm(op1, r8[op2], r8)
  } else if (rm1 && op2 in r16) {
    pushb(137) # 89
    modrm(op1, r16[op2], r16)
  } else if (op1 in r8 && rm2) {
    pushb(138)
    modrm(op2, r8[op1], r8)
  } else if (op1 in r16 && rm2) {
    pushb(139)
    modrm(op2, r16[op1], r16)
  # modrm <-> sreg
  } else if (rm1 && op2 in sreg) {
    pushb(140)
    modrm(op1, sreg[op2], r16)
  } else if (rm2 && op1 in sreg) {
    pushb(142)
    modrm(op2, sreg[op1], r16)
  # reg <- imm
  } else if (op1 in r8) {
    pushb(176+r8[op1])
    pushb(getsym(op2))
  } else if (op1 in r16) {
    pushb(184+r16[op1])
    pushw(getsym(op2))
  # modrm <- imm
  } else if (byteop && rm1) {
    pushb(198)
    modrm(rm1, 0, r16)
  } else if (wordop && rm1) {
    pushb(199)
    modrm(rm1, 0, r16)
  }
}
x86 && op=="push" && op1 in r16 {
  pushb(80+r16[op1])
}
x86 && op=="pop" && op1 in r16 {
  pushb(88+r16[op1])
}
x86 && op=="test" && op2 in r8 { # 84
  pushb(132)
  modrm(op1, r8[op2], r8)
}
x86 && op=="int" { # CD
  pushb(205)
  pushb(getsym(op1))
}
x86 && op=="jmp" {
  pushb(233)
  pushw(getsym(op1)-(pos+3))
}
x86 && op=="call" {
  pushb(232)
  pushw(getsym(op1)-(pos+3))
}
# opcodes with rel8 encoding
x86 && op in ops_rel8 {
  pushb(ops_rel8[op])
  pushb(getsym(op1)-(pos+2))
}
# opcodes without arguments
x86 && op in ops_sb { pushb(ops_sb[op]) }
{
  if (!hex) err("no encoding found")
  submit(pos)
}
END{
  if (of=="hex") printf("\n")
  if (errors) exit(1)
}