use32
.switch [counter]
  .case 1
  .case 2
    mov eax, 2
    .continue
  .case 5
    mov eax, 3
    .switch ebx
      .case 4
        mov eax, 4
      .case 5
        mov eax, 5
      .default
        nop
    .endswitch
    nop
  .default
    nop
.endswitch    

macro .switch variable {
local continue, this, c_style, var
local stat, default, exit
local top, count, here, x, val, location
local save_eax

  continue=0
  this=0
  c_style=0
  save_eax=0
  
  match =c x, variable \{
    var equ x
    c_style=1
    stat equ
  \}
  match =stat x, stat variable \{
    var equ x
  \}
  restore stat

  if ~var eq eax
    save_eax=1
    push eax
    if var in <al, ah, ax, bl, bh, bx, cl, ch, cx, dl, dh, dx, bp, di, si>
      movzx eax, var
    else
      match x y, var \{
        movzx eax, var
        stat equ
      \}
      match =stat, stat \{
        mov eax, var
      \}
      restore stat
    end if
  end if
  label top DWORD
  repeat count
    cmp eax, DWORD 0
    je NEAR $
  end repeat
  if defined default
    jmp default
  else
    if save_eax
      jmp exit-1
    else
      jmp exit
    end if
  end if

  macro .case [value] \{
  \common
    if this
      if c_style | continue
        continue=0
        if save_eax
          jmp $+3
        end if
      else
        jmp exit
        align 16
      end if
    end if
    continue=0
  virtual
    dd $
    load here DWORD from $$
  end virtual
    if save_eax
      pop eax
    end if
  \forward
    this=this+1
    match =stat a-b, stat value \\{
      x equ a
      val equ b
      stat equ
    \\}
    match =stat b, stat value \\{
      x equ
      val equ b
    \\}
    restore stat
    location=top+(11*this)
    if ~x eq
      if x<>0
        store DWORD x at location-10           ;  cmp eax, DWORD x
        store DWORD 11 at location-4
        store BYTE 82h at location-5           ;  jb .1
        this=this+1
        location=location+size
      end if
      store DWORD val at location-10           ;  cmp eax, DWORD val
      store DWORD here-location at location-4
      store BYTE 86h at location-5             ;  jbe here
    else                                       ;.1:
      store DWORD val at location-10           ;  cmp eax, DWORD val
      store DWORD here-location at location-4  ;  je here
    end if
  \}
  
  macro .break arg \{
    match =.if x, arg \\{
      JCOND exit, x
      stat equ
    \\}
    match =stat, stat \\{
      jmp exit
    \\}
    restore stat
  \}
  
  macro .continue \{
    continue=1
  \}
  
  macro .default \{
    if c_style | continue
      continue=0
      if save_eax
        jmp $+3
      end if
    else
      jmp exit
      align 16
    end if
  default:
    if save_eax
      pop eax
    end if
  \}

  macro finish@switch \{
    count=this
    if save_eax
      jmp $+3
      pop eax
    end if
  exit:
  \}

  macro .table \{
  local cmin, cmax
  local min, max, switch_table
  local counter
  local start, next, tab
  tab=1
  cmin=0FFFFFFFFh
  cmax=0
    if this
      if c_style
        if save_eax
          jmp next+1
        else
          jmp next
        end if
      else
        if continue
          continue=0
          if save_eax
            jmp next+1
          else
            jmp next
          end if
        else
          jmp exit
        end if
      end if
    else
      continue=0
    end if
    this=this+1
    location=top+(11*this)
    if min
      store DWORD min at location-10           ;  cmp eax, DWORD min
      store DWORD 11 at location-4
      store BYTE 82h at location-5             ;  jb .1
      this=this+1
      location=location+11
    end if
    store DWORD max at location-10             ;  cmp eax, DWORD max
    store DWORD start-location at location-4
    store BYTE 86h at location-5               ;  jbe start
  start:                                       ;.1:
    jmp [switch_table+(eax-min)*4]
    align 4
    label switch_table DWORD
    times max+1-min dd exit
  next:
  
    macro .case [value] \\{
    \\common
      if ~tab
        if c_style | continue
          continue=0
          if save_eax
            jmp $+3
          end if
        else
          jmp exit
          align 16
        end if
      end if
      tab=0
      continue=0
    virtual
      dd $
      load here DWORD from $$
    end virtual
      if save_eax
        pop eax
      end if
    \\forward
      match =stat a-b, stat value \\\{
        x equ a
        val equ b
        stat equ
      \\\}
      match =stat b, stat value \\\{
        x equ
        val equ b
      \\\}
      restore stat
      if val>cmax
        cmax=val
      end if
      if ~x eq
        if x<cmin
          cmin=x
        end if
        if x<>0
          counter=val-x+1
        else
          counter=val+1
        end if
      else
        if val<cmin
          cmin=val
        end if
        counter=1
      end if
      location=switch_table+(val-min)*4
      repeat counter
        store DWORD here at location
        location=location-4
      end repeat
    \\}
     
    macro finish@table \\{
      max=cmax
      min=cmin
    \\}
  \}
}
  
macro .endtable {
  finish@table
  purge .case, finish@table
}

macro .endswitch {
  finish@switch
  purge .case, .break, .continue, .default, finish@switch
}    

cmp [mem32], imm32
jne  @F

@@:
cmp reg32, xxx
jne  @F

@@:

...
    

Could you write a version, that optimally combines jump tables and comparisons?

  if cases>3 & slots<(cases*2)
    jump_table
  else
    comparisons
  end if    

  .switch <variable>
    .case 1
    .case 5
    .table
      .case 10
      .case 11
      .case 12
      .case 13
    .endtable
    .case 20
  .endswitch    

Or how about mixing jump tables and comparisons in the same switch block?

use32
  .switch
    .case 1
    .case 2
    .table
      .case 3
      .case 4
    .endtable
    .case 5
    .default
  .endswitch