macro   cipher  m
        local   char,low,high,hex8,hex16l,hex16h
        char    substr  <m>,1,1
        low     catstr  char,<l>
        high    catstr  char,<h>
        irp     rch,<al,ah,bl,bh,cl,ch,dl,dh>
         ifidni <m>,<rch>
          sub   m,'0'
          cmp   m,10
          jb    hex8
          sub   m,7
        hex8:
          and   m,0Fh
          exitm
         endif
        endm
        irp     rch,<ax,bx,cx,dx>
         ifidni <m>,<rch>
          sub   m,'00'
          cmp   low,10
          jb    hex16l
          sub   low,7
        hex16l:
          cmp   high,10
          jb    hex16h
          sub   high,7
        hex16h:
          and   m,0F0Fh
          exitm
         endif
        endm
endm    cipher    

macro cipher m {
  irps reg, a b c d \{
    irps half, l h \\{
      match =m, reg\\#half \\\{
      \\\local ..
          sub m, '0'
          cmp m, 10
          jb  ..
          sub m, 7
        ..:
          and m, 0Fh
      \\\}
    \\}
    match =m, reg\#x \\{
      sub m, '00'
      irps half, l h \\\{
      \\\local ..
          cmp reg\\\#half, 10
          jb  ..
          sub reg\\\#half, 7
        ..:
      \\\}
      and m, 0F0Fh
    \\}
  \}
}