With ABCD on 68000, am I right that you need the halfcarry bit in order to use a DAA table?
That's the conclusion I've come to anyway... in fact the only way I can think of to do ABCD on ARM...which has no halfcarry bit and no daa or das instructions... is this:
ot(";@ Add units into r2:\n"); ot(" and r2,r10,#0x0f\n"); ot(" and r0,r1, #0x0f\n"); ot(" add r2,r2,r0\n"); ot(" cmp r2,#0x0a ;@ Decimal adjust units\n"); ot(" addge r2,r2,#0x06\n"); ot("\n"); ot(";@ Add tens into r3:\n"); ot(" and r3,r10,#0xf0\n"); ot(" and r0,r1, #0xf0\n"); ot(" add r3,r3,r0\n"); ot(" add r1,r3,r2 ;@ Add tens and units into r1\n"); ot(" cmp r1,#0xa0 ;@ Decimal adjust tens\n"); ot(" addge r1,r1,#0x60\n");
Haven't added flags and SBCD yet. I mean that's not too bad a routine since abcd isn't used a lot, but will it cater for all the undocumented non decimal cases, e.g 0xfe 0x2b or something ??
update  Thanks for the notes Bart! Also, can you think of a better way on ARM, or is that it do you think?
Cyclone is *almost* there... ;) just a few bits and bugs to go
For completeness here is my SBCD:
ot(";@ Sub units into r2:\n"); ot(" and r2,r1, #0x0f\n"); ot(" and r0,r10,#0x0f\n"); ot(" subs r2,r2,r0\n"); ot(" sublt r2,r2,#0x06\n"); ot(";@ Sub tens into r3:\n"); ot(" and r3,r1, #0xf0\n"); ot(" and r0,r10,#0xf0\n"); ot(" sub r3,r3,r0\n"); ot(" adds r1,r3,r2 ;@ Add tens and units into r1\n"); ot(" sublt r2,r2,#0x60\n");
Seems to work for Ghouls N Ghosts. Haven't thought about flags yet...
You learn something old everyday...
