Dividend DS 6 Divisor DS 3 Temp DS 3 BitCount DS 1 ;********************************************************************** ; ;48 BY 23 BIT UNSIGNED DIVISION (Non-restoring method) ; ;********************************************************************** ; ; Input: Dividend, 6 bytes (Dividend+0 MSB, ... , Dividend+5 LSB) ; Divisor, 3 bytes (Divisor+0 MSB, ... , Divisor+2 LSB) ; ; Output: Dividend, 6 bytes (Dividend = Dividend / Divisor) ; Z - division by zero ; NZ - okay ; ; Temporary: Temp, 3 bytes - remainder ; BitCount, 1 byte - counter ; ; Size: 52 instructions ; ;Max timing: 3+5+6+28*48-2+7+3=1366 cycles ; ;********************************************************************** DIVIDE_48by23 ; Test for zero division mov W, Divisor or W, Divisor+1 or W, Divisor+2 snz ret ; divisor = zero, not possible to calculate - ; return with set zero flag (Z) ; clear remainder clr Temp clr Temp+1 clr Temp+2 mov W, #48 ; initialize bit counter mov BitCount, W stc ; set carry to perform subtraction ; first in the following loop DIVIDE_LOOP_48by23 ; shift in next result bit and ; shift out next bit of dividend rl Dividend+5 rl Dividend+4 rl Dividend+3 rl Dividend+2 rl Dividend+1 rl Dividend ; shift in highest bit from dividend through carry in temp rl Temp+2 rl Temp+1 rl Temp mov W, Divisor+2 ; load w with LSB of divisor ; to use it in subtraction or ; addition afterwards ; If previous result bit was set (subtraction was performed ; without borrow or addition made the remainder positive), ; subtract divisor from remainder, ; else add divisor to remainder sb Dividend+5.0 jmp Div48by23_add ; subtract 23 bit divisor from 24 bit temp, ; divisor LSB is in w sub Temp+2, W ; subtract LSB mov W, Divisor+1 ; get middle byte sc ; if overflow ( from prev. subtraction ) movsz W, ++Divisor+1 ; incresase source sub Temp+1, W ; and subtract from dest. mov W, Divisor ; get top byte sc ; if overflow ( from prev. subtraction ) movsz W, ++Divisor ; increase source sub Temp, W ; and subtract from dest. jmp DIVIDE_NEXT_48by23 ; jump to loop end Div48by23_add ; add 23 bit divisor to 24 bit temp ; divisor LSB is in w add Temp+2, W ; add LSB mov W, Divisor+1 ; middle byte snc ; check carry for overflow from previous addition movsz W, ++Divisor+1 ; if carry set we add 1 to the source add Temp+1, W ; and add it if not zero mov W, Divisor ; MSB byte snc ; check carry for overflow from previous addition movsz W, ++Divisor add Temp, W ; add DIVIDE_NEXT_48by23 ; carry contains next result bit decsz BitCount ; decrement loop counter (carry not influenced) jmp DIVIDE_LOOP_48by23 ; another run ; finally shift in the last carry rl Dividend+5 rl Dividend+4 rl Dividend+3 rl Dividend+2 rl Dividend+1 rl Dividend clz ; done, clear zero flag (NZ) and ret ; return ;**********************************************************************

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