Cannon, Forgive my stupid question: why do you need to convert the hex string to number? Can’t you simply use it as your RFID? (of course you’d have to increase your key field to 16 chars). You’re already handling it as a string, why change?
> On Apr 17, 2017, at 6:36 PM, Cannon Smith via 4D_Tech <4d_tech@lists.4d.com> > wrote: > > I have a little problem I’m hoping someone can help me solve. First, a bit of > background. Our application deals with RFID tags for animals. These are > always 15 digit numbers like 124000123456789. Even though they are numbers, I > never have to deal with them as numbers. Instead, I always treat them as > strings. RFID readers are usually RS-232 devices that send the tag number > over as a string, so that works out well. > > Now I’m being asked to support a new kind of reader that works differently. I > have the algorithm to convert from the reader byte structure to a 15 digit > number. Unfortunately, 4D’s C_REAL variables are only precise to 13 digits, > so my last 2-3 digits are incorrect. I’m hoping someone knows how to convert > what I’m getting into a 15 digit string in some other way. > > Here is an example string coming across the wire: “02ABC877FAFB0200”. This > represents 8 bytes in little endian ordering. The algorithm that was given me > was to break the string into bytes (“02”, “AB”, “C8”, etc.) and then loop > through each byte, converting it to decimal and applying a little math. For > example: > > Hex “02” = Decimal 2. SubValue = 2 * (256^0) = 2 > Hex “AB" = Decimal 171. Subvalue = 171 * (256^1) = 43776 > Hex “C8" = Decimal 200. Subvalue = 200 * (256^2) = 13107200 > Hex “77" = Decimal 119. Subvalue = 119 * (256^3) =1996488704 > Hex “FA" = Decimal 250. Subvalue = 250 * (256^4) = 1073741824000 > Hex “FB" = Decimal 251. Subvalue = 251 * (256^5) = 275977418571776 (4D > gives 2.759774185718e+14) > Hex “02" = Decimal 2. Subvalue = 2 * (256^6) = 562949953421312 > (4D gives 5.629499534213e+14) > Hex “00" = Decimal 0. Subvalue = 0 * (256^7) = 0 > > Once this is done, all the subvalue results are summed which should give the > RFID number. In this case it should be 840003123456770. But 4D gives this: > 8.400031234568e+14. As you can see, the last three digits are not correct. > > So, does anyone know a way to convert the string “02ABC877FAFB0200” to the > string “840003123456770” within 4D’s limitations? > > Thanks. > > -- > Cannon.Smith > Synergy Farm Solutions Inc. > Hill Spring, AB Canada > 403-626-3236 > <can...@synergyfarmsolutions.com> > <www.synergyfarmsolutions.com> > > > ********************************************************************** > 4D Internet Users Group (4D iNUG) > FAQ: http://lists.4d.com/faqnug.html > Archive: http://lists.4d.com/archives.html > Options: http://lists.4d.com/mailman/options/4d_tech > Unsub: mailto:4d_tech-unsubscr...@lists.4d.com > ********************************************************************** -- Julio Carneiro jjfo...@gmail.com ********************************************************************** 4D Internet Users Group (4D iNUG) FAQ: http://lists.4d.com/faqnug.html Archive: http://lists.4d.com/archives.html Options: http://lists.4d.com/mailman/options/4d_tech Unsub: mailto:4d_tech-unsubscr...@lists.4d.com **********************************************************************
