-DenHighZero:
- mov.w A0E,A2
- mov.b A2H,S0L
- mov.b A2L,A2H
- mov.b A0H,A2L
- mov.w A2,A0E
- mov.b A0L,A0H
- mov.b #0,A0L
- mov.b #24,S2H ; only do 24 iterations
-
-nextbit:
- shll.l A0P ; double the answer guess
- rotxl.l S0P ; double remainder
- sub.l A1P,S0P ; does it all fit?
- bhs setone
-
- add.l A1P,S0P ; no, restore mistake
- dec S2H
- bne nextbit
- rts
-
-setone:
- inc A0L
- dec S2H
- bne nextbit
+ ; er0 = er0 / er1
+ ; er3 = er0 % er1
+ ; trashes er1 er2
+ ; expects er1 >= 2^16
+DenHighNonZero:
+ mov.l er0,er3
+ mov.l er1,er2
+#ifdef __H8300H__
+divmod_L21:
+ shlr.l er0
+ shlr.l er2 ; make divisor < 2^16
+ mov.w e2,e2
+ bne divmod_L21
+#else
+ shlr.l #2,er2 ; make divisor < 2^16
+ mov.w e2,e2
+ beq divmod_L22A
+divmod_L21:
+ shlr.l #2,er0
+divmod_L22:
+ shlr.l #2,er2 ; make divisor < 2^16
+ mov.w e2,e2
+ bne divmod_L21
+divmod_L22A:
+ rotxl.w r2
+ bcs divmod_L23
+ shlr.l er0
+ bra divmod_L24
+divmod_L23:
+ rotxr.w r2
+ shlr.l #2,er0
+divmod_L24:
+#endif
+ ;; At this point,
+ ;; er0 contains shifted dividend
+ ;; er1 contains divisor
+ ;; er2 contains shifted divisor
+ ;; er3 contains dividend, later remainder
+ divxu.w r2,er0 ; r0 now contains the approximate quotient (AQ)
+ extu.l er0
+ beq divmod_L25
+ subs #1,er0 ; er0 = AQ - 1
+ mov.w e1,r2
+ mulxu.w r0,er2 ; er2 = upper (AQ - 1) * divisor
+ sub.w r2,e3 ; dividend - 65536 * er2
+ mov.w r1,r2
+ mulxu.w r0,er2 ; compute er3 = remainder (tentative)
+ sub.l er2,er3 ; er3 = dividend - (AQ - 1) * divisor
+divmod_L25:
+ cmp.l er1,er3 ; is divisor < remainder?
+ blo divmod_L26
+ adds #1,er0
+ sub.l er1,er3 ; correct the remainder
+divmod_L26: