Post by thread:Dumb Question

hello folks, I know this is a dumb question and I will probably want to crawl into a hole when I get the answer but ..... does anybody have some code to subtract one 16 bit number from another NOT using 2s compliment so that it returns an ABS result with a flag (AKA register) to say if it is negative. P. ==================================== Remember .... Every Silver Lining Has It's Cloud ==================================== Mailto:spam_OUTefocTakeThisOuTcyberstop.net

Peter Baines <.....PICLISTKILLspam@spam@MITVMA.MIT.EDU> wrote: > does anybody have some code to subtract one 16 bit number from > another NOT using 2s compliment so that it returns an ABS result > with a flag (AKA register) to say if it is negative. Peter: This routine computes DEST = DEST - SOURCE. After it executes, the Carry flag is valid (i.e., Carry = 0 if the result is negative, Carry = 1 if the result is zero or positive). Note that the Zero flag is NOT necessarily valid after execution. MOVF SOURCELO,W SUBWF DESTLO MOVF SOURCEHI,W SKPC INCFSZ SOURCEHI,W SUBWF DESTHI -Andy === Andrew Warren - fastfwdKILLspamix.netcom.com === Fast Forward Engineering - Vista, California === http://www.geocities.com/SiliconValley/2499

---------- > Van: Peter Baines <.....efocKILLspam.....CYBERSTOP.NET> > Aan: EraseMEPICLISTspam_OUTTakeThisOuTMITVMA.MIT.EDU > Onderwerp: Dumb question > Datum: dinsdag 3 maart 1998 12:32 > > hello folks, > I know this is a dumb question and I will probably want to crawl into a > hole when I get the answer but ..... does anybody have some code to > subtract one 16 bit number from another NOT using 2s compliment so that it > returns an ABS result with a flag (AKA register) to say if it is negative. > > P. Take the 2's complement of your answer _IF_ you get a Borrow (Not-Carry) from your subtraction. Remember my son, don't fight the force of your opponent, but use it to get what you want .... (You didn't want to use 2's complement, I'm using it twice :-) Greetz, Rudy Wieser

{Quote hidden}>Peter Baines <PICLISTspam_OUTMITVMA.MIT.EDU> wrote: > >> does anybody have some code to subtract one 16 bit number from >> another NOT using 2s compliment so that it returns an ABS result >> with a flag (AKA register) to say if it is negative. > >Peter: > >This routine computes DEST = DEST - SOURCE. After it executes, the >Carry flag is valid (i.e., Carry = 0 if the result is negative, >Carry = 1 if the result is zero or positive). Note that the Zero >flag is NOT necessarily valid after execution. > > MOVF SOURCELO,W > SUBWF DESTLO > MOVF SOURCEHI,W > SKPC > INCFSZ SOURCEHI,W > SUBWF DESTHI > >-Andy > Peter, Try this... returns ABS(DEST-SOURCE) in DEST MOVF SOURCELO,W SUBWF DESTLO MOVF SOURCEHI,W SKPC INCFSZ SOURCEHI,W SUBWF DESTHI ; SKPNC GOTO DONE ; DEST > SOURCE ; COMF DESTLO ; NEGATE if SOURCE > DEST INCF DESTLO SKPNZ DECF DESTHI COMF DESTHI DONE ; DEST = ABS( DEST - SOURCE ) I don't know if there is any simpler way, seem like there should be some cleverer way of doing the subtract. Ray Gardiner (DSP Systems) @spam@rayKILLspamdsp-systems.com http://www.dsp-systems.com private email to:- KILLspamrayKILLspamnetspace.net.au

Ok, it's late and I am tired and I can't wrap my head around attaching an LCD with Hitachi controller and a 3x4 keypad to the same single 8-bit port. Some hints would be much appreciated. Adi -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email RemoveMElistservTakeThisOuTmitvma.mit.edu with SET PICList DIGEST in the body