These are some of the noteworthy examples from ORing or XORing with constants.
Taking advantage of the fact that anything ORed with one is one:
Code:
00321 ; 00013 W0 := W1 or $FF00;
0106 D6 35 [3] 00322 ldab W1+1
0108 86 FF [2] 00323 ldaa #$FF
010A 97 38 [4] 00324 staa W0
010C D7 39 [4] 00325 stab W0+1
00326 ; 00014 W0 := W1 or $FF;
010E 96 34 [3] 00327 ldaa W1
0110 C6 FF [2] 00328 ldab #$FF
0112 97 38 [4] 00329 staa W0
0114 D7 39 [4] 00330 stab W0+1
Something XORed with zero is unchanged:
Code:
00331 ; 00015 W0 := B1 xor $9900;
0116 D6 18 [3] 00332 ldab B1
0118 86 99 [2] 00333 ldaa #153
011A 97 38 [4] 00334 staa W0
011C D7 39 [4] 00335 stab W0+1
XORing with one flips the bit. On the 6800, we have an instruction for that. Same speed but only a single byte:
Code:
00336 ; 00016 W0 := W1 xor $FF00;
011E 96 34 [3] 00337 ldaa W1
0120 D6 35 [3] 00338 ldab W1+1
0122 43 [2] 00339 coma
0123 97 38 [4] 00340 staa W0
0125 D7 39 [4] 00341 stab W0+1
00342 ; 00017 W0 := W1 xor $FF;
0127 96 34 [3] 00343 ldaa W1
0129 D6 35 [3] 00344 ldab W1+1
012B 53 [2] 00345 comb
012C 97 38 [4] 00346 staa W0
012E D7 39 [4] 00347 stab W0+1
This is the usual sign extension:
Code:
00348 ; 00018 W0 := S1;
0130 D6 36 [3] 00349 ldab S1
0132 86 7F [2] 00350 ldaa #$7F ; Thanks Mike B!
0134 11 [2] 00351 cba
0135 82 7F [2] 00352 sbca #$7F
0137 97 38 [4] 00353 staa W0
0139 D7 39 [4] 00354 stab W0+1
No need to actually do the sign extension here...
Code:
00355 ; 00019 W0 := S1 or $FF00;
013B D6 36 [3] 00356 ldab S1
013D 86 FF [2] 00357 ldaa #$FF
013F 97 38 [4] 00358 staa W0
0141 D7 39 [4] 00359 stab W0+1
And here we want the inverse of that:
Code:
00360 ; 00020 W0 := S1 xor $FF00;
0143 D6 36 [3] 00361 ldab S1
0145 86 7F [2] 00362 ldaa #$7F ; Thanks Mike B!
0147 11 [2] 00363 cba
0148 89 80 [2] 00364 adca #$80
014A 97 38 [4] 00365 staa W0
014C D7 39 [4] 00366 stab W0+1
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