From: Doug Ingraham: Tuesday, September 13, 2016 1:38 PM
This struck me as a pretty clever bit of code. My first cut used 23 words
including 2 masks and 3 temporaries.
Thanks!!
This is the working version of Vince's original. It uses 18 words
including 1 mask and 2 temporaries.
I have done some edge testing and it appears to work.
30 / THIS VERSION BY VINCE SLYNGSTAD
31 00210 0000 BSWI, .-. /ENTRY POINT
32 00211 3175 DCA SAVEAC
33 00212 7420 SNL /REMEMBER LINK STATE
34 00213 7040 CMA /AS A -1 FOR ISZ TEST
35 00214 3176 DCA SAVEL
36 00215 7100 CLL /NEED THE LINK CLEARED
Ok, I just don't see why one should need to clear link here.
37 00216 1175 TAD SAVEAC /GET 0 XXX XXX YYY YYY
38 00217 0177 AND C7700 / 0 XXX XXX 000 000
These two lines, the comment would have "L" instead of their first "0".
39 00220 1175 TAD SAVEAC / X XXX XX0 YYY YYY
Poof! There goes the prior value of link! And the "0" in the comment
is correct.
40 00221 7006 RTL / X XXX 0YY YYY YXX
41 00222 7006 RTL / X X0Y YYY YYX XXX
42 00223 7006 RTL / 0 YYY YYY XXX XXX
43 00224 2176 ISZ SAVEL /WAS LINK SET?
44 00225 7020 CML /YES, RESTORE LINK
45 00226 5610 JMP I BSWI /RETURN
46 $
As Klemens Krause points out you do need the CLL (line 36) somewhere before
the second TAD SAVEAC or it will flip
what was the original leftmost bit (AC 0).
Someone help me understand this claim.
I have thought about this a bunch and have come up with an improved
version. It also uses 18 words including 2 constants
two temporaries. This is one less instruction executed.
32 00210 0000 BSWI, .-. /ENTRY POINT
33 00211 3174 DCA SAVEAC
34 00212 7430 SZL /REMEMBER LINK STATE
35 00213 1177 TAD C0100 /PRE ROTATE LINK POSITION
36 00214 3175 DCA SAVEL
37 00215 7100 CLL /NEED THE LINK CLEARED
38 00216 1174 TAD SAVEAC /GET 0 XXX XXX YYY YYY
39 00217 0176 AND C7700 / 0 XXX XXX 000 000
40 00220 1174 TAD SAVEAC / X XXX XX0 YYY YYY
41 00221 1175 TAD SAVEL / X XXX XXL YYY YYY
42 00222 7006 RTL / X XXX LYY YYY YXX
43 00223 7006 RTL / X XLY YYY YYX XXX
44 00224 7006 RTL / L YYY YYY XXX XXX
45 00225 5610 JMP I BSWI /RETURN
Not bad but I realized even more was possible.
31 00210 0000 BSWI, .-. /ENTRY POINT
32 00211 3174 DCA SAVEAC
33 00212 7430 SZL /REMEMBER LINK STATE
34 00213 1176 TAD C0100 /PRE ROTATE LINK POSITION
35 00214 7100 CLL /NEED THE LINK CLEARED
36 00215 1174 TAD SAVEAC /GET 0 XXX XXX YYY YYY
37 00216 0175 AND C7700 / 0 XXX XXX 000 000
38 00217 1174 TAD SAVEAC / X XXX XX0 YYY YYY
39 00220 7006 RTL / X XXX LYY YYY YXX
40 00221 7006 RTL / X XLY YYY YYX XXX
41 00222 7006 RTL / L YYY YYY XXX XXX
42 00223 5610 JMP I BSWI /RETURN
Nice!
Vince
