; Divide 16 bit number in R7,R6 by 8 bit number in B. Put result in A. div16: CJNE R6,#0,calcdiv CJNE R7,#0,calcdiv MOV R2,#0 ; If R7:R6 is 0, then result is 0 LJMP dend calcdiv:CLR C MOV A,B RRC A MOV R5,A MOV A,#0 RRC A MOV R4,A ; R5,R4 is the initial divisor MOV R2,#0 ; Result MOV R3,#80h ; Bit value for result dloop: MOV A,R6 CLR C SUBB A,R4 ; LS Byte subtract MOV R1,A MOV A,R7 SUBB A,R5 ; MS Byte subtract JC set0 ; If carry set, subtract was not possible MOV R7,A MOV A,R1 MOV R6,A ; R7,R6 is the new value to subtract from MOV A,R2 ADD A,R3 MOV R2,A ; Set bit in result set0: CLR C MOV A,R3 RRC A MOV R3,A ; New bit value for result JZ dend ; all bits have been done CLR C MOV A,R5 RRC A MOV R5,A MOV A,R4 RRC A MOV R4,A ; R5,R4 is new divisor LJMP dloop ; do next bit dend: MOV A,R2 ; Result in A RET ; Divide 20 bit number in R7:R6:R5 by 10 bit number in R3:R2. ; Put result in A:B. div20: MOV A,R5 ORL A,R6 ORL A,R7 JNZ caldiv SETB RS0 ; Reg bank 1 MOV R7,#0 MOV R6,#0 ; If R7:R6:R5 is 0, then result is 0 CLR RS0 ; Reg bank 0 LJMP d20end caldiv: MOV R4,#0 MOV R1,#3 ; Divisor is already 6 left. Shift another 3. shftsub:CLR C MOV A,R2 RLC A MOV R2,A MOV A,R3 RLC A MOV R3,A MOV A,R4 RLC A MOV R4,A DJNZ R1,shftsub ; R4:R3:R2 is the initial sutractor SETB RS0 ; Reg bank 1 MOV R7,#0 MOV R6,#0 ; Result in R7:R6 bank 1 MOV R5,#80h MOV R4,#0 ; Bit value for result in R5:R4 bank 1 CLR RS0 ; Reg bank 0 d20loop:CLR C MOV A,R5 SUBB A,R2 ; LS Byte subtract MOV R0,A MOV A,R6 SUBB A,R3 ; Mid Byte subtract MOV R1,A MOV A,R7 SUBB A,R4 ; MS Byte subtract JC res0 ; If carry set, subtract was not possible MOV R7,A MOV A,R1 MOV R6,A MOV A,R0 MOV R5,A ; Update subtractee SETB RS0 ; Reg bank 1 MOV A,R6 ORL A,R4 MOV R6,A ; Set bit in result LS Byte MOV A,R7 ORL A,R5 MOV R7,A ; Set bit in result MS Byte res0: SETB RS0 ; Reg bank 1 CLR C MOV A,R5 RRC A MOV R5,A MOV A,R4 RRC A MOV R4,A ; New bit value for result ANL A,#20h CLR RS0 ; Reg bank 0 JNZ d20end ; all bits have been done CLR C MOV A,R4 RRC A MOV R4,A MOV A,R3 RRC A MOV R3,A MOV A,R2 RRC A MOV R2,A ; R4:R3:R2 is the new subtractor LJMP d20loop ; do next bit d20end: SETB RS0 ; Reg bank 1 MOV A,R7 MOV B,R6 ; Result in A:B CLR RS0 ; Reg bank 0 RET
See:
file: /Techref/8051/div32by16-ad.htm, 4KB, , updated: 2007/9/25 14:24, local time: 2024/8/21 13:14,
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