PDP-8 GTF question

[Brian L. Stuart]

> To Stuart - are you sure your code does it right. Could you post it?

That's kind of what got me here.  I was running the 8E-D1HA
maindec on my emulator and it was failing at that point.  My
initial reaction was that I was misinterpreting the RTF behavior
and that perhaps it wasn't setting the interrupt inhibit as I
had thought.  So I ran the diag on the real thing and single
stepped through that part.  Sure enough the RTF does set it,
but GTF seems to not report it.  That's when I got confused
enough to break down and look at other people's code :)

Here's my code for both the RTF and GTF instructions.  Caveat:
it's in MCPL, but it should be close enough to C that it'll be
recognizable what's going on:

: 0, 0, 4 =>					// GTF
	 ac := link << 11 | irq() << 9 | ie << 7 | sf
//	 ac := link << 11 | irq() << 9 | ii << 8 | ie << 7 | sf
: 0, 0, 5 =>					// RTF
	ie := 1
	ii := 1
	link := ac >> 11
	ub := (ac >> 6) & #o1
	ib := (ac >> 3) & #o7
	df := ac & #o7

The line that's commented out on the GTF is the original version
I had where I did include the interrupt inhibit.

For comparison, here's the version in simh:

            case 4:                                     /* GTF */
                LAC = (LAC & 010000) |
                      ((LAC & 010000) >> 1) | (gtf << 10) |
                      (((int_req & INT_ALL) != 0) << 9) |
                      (((int_req & INT_ION) != 0) << 7) | SF;
                break;

            case 5:                                     /* RTF */
                gtf = ((LAC & 02000) >> 10);
                UB = (LAC & 0100) >> 6;
                IB = (LAC & 0070) << 9;
                DF = (LAC & 0007) << 12;
                LAC = ((LAC & 04000) << 1) | iot_data;
                int_req = (int_req | INT_ION) & ~INT_NO_CIF_PENDING;
                break;

 and the one in Doug Jones' emulator:

				case 04: /* GTF */
					ac = (link >> 1)       /* bit 0 */
#ifdef KE8E
					   | (gt?)	       /* bit 1 */
#endif
					   | ((irq > 0) << 9)  /* bit 2 */
#ifdef KM8E
					   | (0)	/*?*/  /* bit 3 */
#endif
					   | (enab << 7)       /* bit 4 */
#ifdef KM8E
					   | sf 	       /* bit 5-11 */
#endif
					;
					break;
				case 05: /* RTF */
					link = (ac<<1)& 010000; /* bit 0 */
#ifdef KE8E
					gt = ?			/* bit 1 */
#endif
					/* nothing */		/* bit 2 */
					/* nothing */		/* bit 3 */
					enab = 1;		/* bit 4 */
#ifdef KM8E
					ub = (ac & 00100) >> 6; /* bit 5 */
					ib = (ac & 00070) << 9; /* bit 6-8 */
					dfr = (ac & 00007) << 12;/* bit 9-11 */
#endif
					/* disable interrupts until branch */
					enab_rtf = 0;
					break;

BLS