Post by thread:16x16 multiplication

Has anybody a 16x16 mutilpy code? Thanks a lot. I tried the one from Microchip but it doesn't work properly all the time: 8AD3h * 0919h : result OK, but if second 16 bit number > 0919, the result shift from about 257, and then the multiplication is OK BUT it has this kind of offset too much. I would appreciate any help. Thanks a lot. David

David BALDWIN wrote: > > Has anybody a 16x16 mutilpy code? Thanks a lot. I tried the one from > Microchip but it doesn't work properly all the time: > > 8AD3h * 0919h : result OK, but if second 16 bit number > 0919, the > result shift from about 257, and then the multiplication is OK BUT it > has this kind of offset too much. I would appreciate any help. Thanks a > lot. > > David Sometimes when i have this kind of problem, i use the Pic C compiler to see how it does a multiplication in Assembly! Miguel.

On Mon, Aug 04, 1997 at 10:15:27AM -0700, WF AUTOMAGCO wrote: > Sometimes when i have this kind of problem, i use the Pic C compiler to > see how it does a multiplication in Assembly! Here's the 16 bit multiply code from our C library. Enjoy. -- Clyde Smith-Stubbs |HI-TECH Software, |Email: spam_OUTclydeTakeThisOuThtsoft.com Ph: +61 7 3354 2411|P.O. Box 103, Alderley,|WWW: http://www.htsoft.com/ Fax: +61 7 3354 2422|QLD, 4051, AUSTRALIA. |PGP: finger .....clydeKILLspam@spam@htsoft.com --------------------------------------------------------------------------- ANSI C for the PIC! Now shipping! See http://www.htsoft.com for more info. Attachment converted: wonderland:wmul.as (TEXT/MSIE) (00003756)

David BALDWIN <baldwinKILLspamETCA.ALCATEL.BE> wrote: >Has anybody a 16x16 mutilpy code? Thanks a lot. I tried the one from >Microchip but it doesn't work properly all the time: David, try this: ;******************************************************************* ; Double Precision Multiplication ; ; n_2 : n_1 * n_4 : n_3 -> q_4:q_3:q_2:q_1 ; ; Standard shift and add. ; Execution time: 215 to 295 clock cycles. ; Code space: 22 locations ; ; Cleaned up and corrected version from Microchip Ap note by BF. ; Note: Ap note has errors! Additional mods by Scott Dattalo. ; ;******************************************************************* mpy16b16: macro local m1, m2 clrf q_4 clrf q_3 clrf q_2 clrf q_1 bsf q_2, 7 m1: rrf n_2, f rrf n_1, f skpc goto m2 movf n_3, w addwf q_3, f movf n_4, w skpnc incfsz n_4, w addwf q_4, f m2: rrf q_4, f rrf q_3, f rrf q_2, f rrf q_1, f skpc goto m1 endm -- Bob Fehrenbach Wauwatosa, WI .....bfehrenbKILLspam.....execpc.com

Bob Lunn 08/05/97 10:12 AM > Thanks for multiply routines, but I had like to have > the corrections to bring ti Mchip one to put it to work. > Any idea? Not an idea (?) but a comment and suggestion. Comment. Why bother? Suggestion. You now have at least a couple of implementations of 16x16 multiply. By studying these known good implementations you will quickly understand what is required. Apply your new found knowledge to the task of repairing Mchip's broken code. ___Bob