convert integer to base 64 and back again

[kevin]

 This PlayBASIC source code provides two functions; one to convert a base 10 value into base 64 and the inverse function to convert a base 64 back to base 10

 

PlayBASIC Code: [Select]

   //  characters used to represent each digit in our base 64 number
   global Digits_key$="0123456789aAbBcCdDeEfFgGhHiIjJkKlLmMnNoOpPqQrRsStTuUvVwWxXyYzZ_@"

   //  table to help use convert back from numbers in our base 64 string
   dim Decode_Digits(255)
   for lp=1 to len(Digits_key$)
      ThisCHR=mid(Digits_Key$,lp)
      Decode_Digits(ThisCHR)=lp-1
   next



   for lp =0 to 10
         Value=rnd($7fffffff)
         key$=EncodeInt64(Value)
         Result =DecodeInt64(Key$)
         print "Value="+str$(Value)+ "   "+Key$+" = "+str$(Result)
   next



   print "Range Test Start."

   max=$7fff
   For lp =0 to max 
      key$=EncodeInt64(lp)
      Value =DecodeInt64(Key$)
      if lp<>Value
            print "error: " + key$ + " = " +str$(lp)+" <> "+str$(Value)
      endif
      if abs(timer()-CurrentTime) >200
         CurrentTime=timer()
         Sync   
      endif         
   next

   print "Test Over ......"

   sync
   waitkey
      

Function EncodeInt64(ThisValue)
      //  max digits within a 32bit integer
      Digits= 32/6
      for Digit=0 to Digits-1
            Value= ThisValue and 63
            ThisValue = ThisValue >> 6
            Result$ =mid$(Digits_key$,Value+1)+Result$
      next
EndFunction Result$


Function DecodeInt64(Number$)
      for Digit=1 to Len(Number$)
            Value= Decode_Digits(mid(Number$,Digit))
            Result = (Result << 6) or Value
      next
EndFunction Result