CHAR ARRAY digits="0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz!"

INT FUNC MyMod(INT a,b)
  IF b>=0 THEN
    RETURN (a MOD b)
  FI
RETURN (a-(b*(a/b)))

PROC Encode(INT n,base CHAR ARRAY res)
  INT i,d,len
  CHAR tmp

  IF base<-63 OR base>-1 THEN Break() FI
  IF n=0 THEN SAssign(res,"0") FI

  len=0
  WHILE n#0
  DO
    d=MyMod(n,base)
    n==/base
    IF d<0 THEN
      n==+1
      d==-base
    FI
    len==+1
    res(len)=digits(d+1)
  OD
  res(0)=len

  FOR i=1 to len/2
  DO
    tmp=res(i)
    res(i)=res(len-i+1)
    res(len-i+1)=tmp
  OD
RETURN

BYTE FUNC Index(CHAR ARRAY s CHAR c)
  BYTE i

  FOR i=1 TO s(0)
  DO
    IF s(i)=c THEN RETURN (i) FI
  OD
RETURN (0)

INT FUNC Decode(CHAR ARRAY s INT base)
  INT res,b,i,pos

  IF base<-63 OR base>-1 THEN Break() FI
  IF s(0)=1 AND s(1)='0 THEN RETURN (0) FI

  res=0
  b=1
  pos=s(0)
  WHILE pos>=1
  DO
    i=Index(digits,s(pos))-1
    res==+i*b
    b==*base
    pos==-1
  OD
RETURN (res)

PROC Test(INT n,base)
  CHAR ARRAY s(20)
  INT v

  Encode(n,base,s)
  PrintF("%I encoded in base %I is %S%E",n,base,s)
  v=Decode(s,base)
  PrintF("%S decoded in base %I is %I%E%E",s,base,v)
RETURN

PROC Main()
  INT v
  Test(10,-2)
  Test(146,-3)
  Test(15,-10)
  Test(-568,-63)
RETURN