how can I display a 64 bit number (2 longs) as decimal

phishguy

I am working on software to decode a RFID chip that has a 64 bit ID. I know that it will be easy to display the hexadecimal value. However, I need to be able to display it as decimal. I actually only need the least significant 37 bits. How would I go about doing this?
·

Mike Green

You need to write a multiple precision divide by 10 routine that produces a dividend and remainder. It's really easy if you divide up the number into 24 bit pieces like this:

var
   long dividend[noparse][[/noparse] 2 ]
   byte buffer[noparse][[/noparse] 25 ]

pub convert | i
   ' return the starting address of a string with the decimal value
   result := @buffer[noparse][[/noparse]24]
   byte[noparse][[/noparse]result]~
   repeat
      byte[noparse][[/noparse]--result] := divBy10 + "0"
   while dividend[noparse][[/noparse] 0 ] or dividend[noparse][[/noparse] 1 ]

pri divBy10 | i, temp
   result := 0
   repeat i from 1 to 0
      temp := (result << 24) | dividend[noparse][[/noparse] i ]
      result := temp // 10
      dividend[noparse][[/noparse] i ] := temp / 10

phishguy

That was quick. Thanks a bunch.

phishguy

OK, forgive me for being dense and a noob. But, I can't figure out how to use that function. Could you show me an example using VGA_TEXT for output and an input example of $0000001B· $F21B02CA ?

Mike Green

You'd set "dividend[noparse][[/noparse] 1 ] := $001BF2" and "dividend[noparse][[/noparse] 0 ] := $1B02CA", then you'd call "vga.str(convert)" (assuming that "vga" is the object name of "VGA_TEXT").

Bobb Fwed

You can't break it up into a byte output? "0F04029599" this is an 80-bit RFID value of one of my cards. With the cards I am using all the bytes are within displayable-byte-values that look like a hex value (0..9 or A..F). I think this is a very common way to input/output values, it's fast (enough), easy to read, and easy to input.

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phishguy

OK, that sorta works. I get 20025973450 as a result when I should get 120025973450.

Mike Green

I don't understand why it doesn't produce the leftmost digit. It should output all the digits until the dividend is zero with a minimum of 1 digit.

phishguy

OK, I figured out how to get the first digit. Now I have a problem where I get 16 leading spaces when I send it to the screen.

''***************************************
''*  VGA Text Demo v1.0                 *
''*  Author: Chip Gracey                *
''*  Copyright (c) 2006 Parallax, Inc.  *
''*  See end of file for terms of use.  *
''***************************************

CON

  _clkmode = xtal1 + pll16x
  _xinfreq = 5_000_000

OBJ

  text : "vga_text"
  
Var
   long dividend[noparse][[/noparse] 2 ]
   byte buffer[noparse][[/noparse] 13 ]

PUB start | i
     
    dividend[noparse][[/noparse]1] := $1BF2
    dividend[noparse][[/noparse]0] := $1B02CA
     
  'start term
  text.start(16)
  text.str(string("12345678901234567890",13,10))
  
  text.str(convert)
  
 
pub convert | i
   ' return the starting address of a string with the decimal value
   result := @buffer[noparse][[/noparse]12]
   byte[noparse][[/noparse]result]~
   repeat
      byte[noparse][[/noparse]--result] := divBy10 + "0"
   while dividend[noparse][[/noparse] 0 ] or dividend[noparse][[/noparse] 1 ]  
  byte[noparse][[/noparse]--result] := divBy10 + "0"

pri divBy10 | i, temp
   result := 0
   repeat i from 1 to 0
      temp := (result << 24) | dividend[noparse][[/noparse] i ]
      result := temp // 10
      dividend[noparse][[/noparse] i ] := temp / 10

Phil Pilgrim (PhiPi)

phishguy,

I ran your program using tv_text instead of vga_text and didn't see any leading spaces. I also eliminated your extra byte[noparse][[/noparse]--result] := divBy10 + "0", since it was giving me a leading zero.

-Phil

Timmoore

I tried it with a serial port and got the same results as Phil

phishguy

weird! Why am I getting different results? Maybe it has something to do with VGA_text.

Timmoore

dec 10 is special to the vga text, try removing this from the end of your first string, i.e.

text.str(string("12345678901234567890",13))

phishguy

Doh! You're right. That bit me before and I completely forgot about it.

Thanks! All is well now.

VIRAND

There was a simple algorithm that requires only decimal addition I think it goes like this (pseudo code).

n = binary number to convert to decimal string

dec2add:="1",0 'NOT VALID SPIN set one decimal string to 1
str:="0",0 'NOT VALID SPIN set output decimal string to 0
repeat until n==0
if n&1 = 1
_adddec (str, dec2add) 'NOT VALID SPIN str := str+dec2add
n=n/2 'divide by 2
adddec (dec2add,dec2add) 'NOT VALID SPIN dec2add := dec2add x 2

Adddec would be a simple chalkboard addition of the second string to the first.
I tried to describe it more but I made it sound too complicated.