Post by thread:Multiplication

At 02:44 PM 2/24/97 -0600, you wrote: >Why can't I use multiplication with MPLABC and the 16C63? I get all kinds >of errors when I attempt it. Is it not possible, or am I doing something >wrong? The 16C parts don't have hardware multiply. If using software, how about posting the routine. Andy ================================================================== Andy Kunz - Montana Design - 409 S 6th St - Phillipsburg, NJ 08865 Hardware & Software for Industry & R/C Hobbies "Go fast, turn right, and keep the wet side down!" ==================================================================

This code: long i, j; i =j*5; causes these errors: ERROR C:\MPLAB\MPLABC14.LIB 20:16:ILLEGAL OR UNDEFINED ARGUMENT _t 1 ERROR C:\MPLAB\MPLABC14.LIB 21:7:EXPECTED ;, ERROR C:\MPLAB\MPLABC14.LIB 21:7:EXPECTED , got s ERROR C:\MPLAB\MPLABC14.LIB 24:5:ILLEGAL OR UNDEFINED ARGUMENT R1 .. 6 ERROR C:\MPLAB\MPLABC14.LIB 25:5:ILLEGAL OR UNDEFINED ARGUMENT R1 .. 6 ERROR C:\MPLAB\MPLABC14.LIB 26:5:ILLEGAL OR UNDEFINED ARGUMENT R1 .. 6 ERROR C:\MPLAB\MPLABC14.LIB 27:12:ILLEGAL OR UNDEFINED ARGUMENT R1 .. 6 ERROR C:\MPLAB\MPLABC14.LIB 35:14:ILLEGAL OR UNDEFINED ARGUMENT _r 2 ERROR C:\MPLAB\MPLABC14.LIB 36:14:ILLEGAL OR UNDEFINED ARGUMENT _q 2 ERROR C:\MPLAB\MPLABC14.LIB 37:14:ILLEGAL OR UNDEFINED ARGUMENT _s 2 I find this very disturbing since a file named ctutor.c which shipped with the compiler contains this code: #include <16c54.h> #include <math.h> unsigned int Num1=2, Num2=3; // Declare two eight bit numbers. unsigned long Num3; // Declare one long for the result. unsigned int Num3High @ &Num3+1; // Create an address for the top byte. void main() { while(1) { Num3 = Num1 * Num2; // Multiply the two bytes into a long. } } Thanks, David Novak Hopkins Mfg. .....novakKILLspam@spam@valu-line.net ---------- > From: Andy Kunz <montanaKILLspamFAST.NET> > To: .....PICLISTKILLspam.....MITVMA.MIT.EDU > Subject: Re: Multiplication > Date: Monday, February 24, 1997 5:25 PM > > At 02:44 PM 2/24/97 -0600, you wrote: > >Why can't I use multiplication with MPLABC and the 16C63? I get all kinds {Quote hidden}> >of errors when I attempt it. Is it not possible, or am I doing something > >wrong? > > The 16C parts don't have hardware multiply. > > If using software, how about posting the routine. > > Andy > ================================================================== > Andy Kunz - Montana Design - 409 S 6th St - Phillipsburg, NJ 08865 > Hardware & Software for Industry & R/C Hobbies > "Go fast, turn right, and keep the wet side down!" > ==================================================================

> Hi, > > I needed some help in multiplication. > > I needed to multiply a 24 and a 8 bit number -> result 32 bits You can do it the old fashioned shift and add method. Take the 24 bit value and for each of the 8 bits, shift it one bit to the left. The rlf instruction for each of the 4 bytes (because once you start shifting the 24 bits will expand to 32 bits) will do the job. Then for each bit in the 8 bit multiplicand, if it's a one add it to the product. Something like this: -------------------- mult24x8: clrf prod0 ; Clear the product clrf prod1 clrf prod2 clrf prod3 clrf twofour3 ; Clear the top byte of the multiplicand multloop: movf eight,W ; Check to see if eight bit is empty btfsc STATUS,Z ; Done if zero return bcf STATUS,C ; clear carry rrl eight,F ; Get the next bit btfss STATUS,C ; Add if carry is set goto multshift ; shift only if 0 movf twofour0,W ; Add the 32 bits of multiplicand to product addwf prod0,F ; each addwf sets the carry btfsc STATUS,C ; Don't increment if no carry incf prod1,F ; Add one to next byte if carry occured movf twofour1,W ; addwf prod1,F ; btfsc STATUS,C ; Don't increment if no carry incf prod2,F ; Add one to next byte if carry occured movf twofour2,W ; addwf prod2,F ; btfsc STATUS,C ; Don't increment if no carry incf prod3,F ; Add one to next byte if carry occured movf twofour3,W ; addwf prod3,F ; multshift: bcf STATUS,C ; clear carry rlf twofour0,F ; Shift the 24 bits one bit to the left rlf twofour1,F rlf twofour2,F rlf twofour3,F goto multloop ------------------------------------------------------------ I wrote this off the top of my head and I haven't tested it, but it should be in the ballpark. Not speedy, but should work. BAJ > > Also, could someone please explain how the comf instruction works... > > eg. comf 1111 -> 0000 ? Is that right? Yes. it just flips each bit. BAJ

See: http://www.piclist.com/faq under routines / math / basic math Also, please don't post in HTML to the PICList. See http://www.piclist.com --- James Newton (PICList Admin #3) EraseMEjamesnewtonspam_OUTTakeThisOuTpiclist.com 1-619-652-0593 PIC/PICList FAQ: http://www.piclist.com or .org -----Original Message----- From: pic microcontroller discussion list [PICLISTspam_OUTMITVMA.MIT.EDU]On Behalf Of Saurabh Sinha Sent: Saturday, March 11, 2000 09:17 To: @spam@PICLISTKILLspamMITVMA.MIT.EDU Subject: Multiplication Hi, I needed some help in multiplication. I needed to multiply a 24 and a 8 bit number ==> result 32 bits Also, could someone please explain how the comf instruction works... eg. comf 1111 = 0000 ? Is that right? Thanks in advance for your help. Saurabh