.define .dvi4 .sect .text .sect .rom .sect .data .sect .bss .sect .text ! 32 bits integer divide and remainder routine ! Bit 0 of a-reg is set iff quotient has to be delivered ! Bit 7 of a-reg is set iff the operands are signed, so: ! Expects in a-reg: 0 if called by rmu 4 ! 1 if called by dvu 4 ! 128 if called by rmi 4 ! 129 if called by dvi 4 ! Expects on stack: divisor ! dividend ! Yields on stack: quotient or remainder .dvi4: pop h shld .retadr mov h,b mov l,c shld .bcreg sta .areg pop h ! store divisor shld block3 xchg pop h shld block3+2 dad d jc 1f mov a,l ora h cz eidivz ! trap if divisor = 0 1: pop h ! store dividend shld block1 pop h shld block1+2 lxi h,0 ! store initial value of remainder shld block2 shld block2+2 mvi b,0 lda .areg ral jnc 2f ! jump if unsigned lda block1+3 ral jnc 1f mvi b,129 lxi h,block1 call compl ! dividend is positive now 1: lda block3+3 ral jnc 2f inr b lxi h,block3 call compl ! divisor is positive now 2: push b ! save b-reg mvi b,32 dv0: lxi h,block1 ! left shift: block2 <- block1 <- 0 mvi c,8 xra a 1: mov a,m ral mov m,a inx h dcr c jnz 1b lxi h,block2+3 ! which is larger: divisor or remainder? lxi d,block3+3 mvi c,4 1: ldax d cmp m jz 0f jnc 3f jmp 4f 0: dcx d dcx h dcr c jnz 1b 4: lxi d,block2 ! remainder is larger or equal: subtract divisor lxi h,block3 mvi c,4 xra a 1: ldax d sbb m stax d inx d inx h dcr c jnz 1b lxi h,block1 inr m 3: dcr b jnz dv0 ! keep looping pop b lda .areg ! quotient or remainder? rar jnc 4f ! for dvi 4 and dvu 4 only: mov a,b rar lxi h,block1 ! complement quotient if divisor cc compl ! and dividend have different signs lhld block1+2 ! push quotient push h lhld block1 push h jmp 5f ! for rmi 4 and rmu 4 only: 4: mov a,b ral lxi h,block2 cc compl ! negate remainder if dividend was negative lhld block2+2 push h lhld block2 push h 5: lhld .bcreg mov b,h mov c,l lhld .retadr pchl ! make 2's complement of 4 bytes pointed to by hl. compl: push b mvi c,4 xra a 1: mvi a,0 sbb m mov m,a inx h dcr c jnz 1b pop b ret