;email@example.com ;unsigned multiply of a2:a1 with b2:b1 leaving result in res4:res3:res2:res1 ; These 8 variables need to be defined ; ; Program length 32 line ; time 129 to 228 cycles ; This program looks at the lsb of a1 to decide whether to add b1 to res2 ; ; and b2 to res3, with appropriate carrys ; It then looks at the lsb of a2 to decide whether to add b1 to res3 and ; b2 to res4, again with appropriate carrys. ; The rotates then only have to be done 8 times ; ; This is uses slightly more program but takes a little less time than ; a routine that performs one 16 bit addition per rotate and 16 rotates ; ; Multiple byte addition routine from Microchip AN617 ; Result registers used as loop counter from Bob Fehrenbach & Scott Dattalo ; clrf res4 clrf res3 clrf res2 movlw 0x80 movwf res1 nextbit rrf a2,f rrf a1,f btfss status, carry goto nobit_l movf b1,w addwf res2,f movf b2, w btfsc status, carry incfsz b2, w addwf res3, f btfsc status, carry incf res4, f bcf status, carry nobit_l btfss a1, 7 goto nobit_h movf b1,w addwf res3,f movf b2, w btfsc status, carry incfsz b2, w addwf res4, f nobit_h rrf res4,f rrf res3,f rrf res2,f rrf res1,f btfss status, carry goto nextbit
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