From: terje.mathisen@nospicedham.tmsw.no   
      
   James Harris wrote:   
   > One more "wheel", though, just out of interest. I see that of the   
   > opcodes available there are, in hex, these "ranges":   
   >   
   > the 3x range which gives some very useful xor and cmp the 7x range   
   > which provides short jumps _if_ offsets fit   
      
   Exactly right. :-)   
   >   
   > but there are not many useful instructions available. Has it already   
   > been looked at to xor a run of bytes in order to make some other   
   > opcode ranges available (and maybe make jCC offsets more amenable)?   
      
   We use XOR in the SMC part to change known legal ascii values into the   
   desired opcode bytes.   
      
   > I've not worked out any particular xor value. Just asking if it's   
   > already been considered.   
      
   In my code I added one more (strong!) limitation: I wanted to write a   
   primary decoder that would work with as little self-modification as   
   possible, so when I figured out a way that only needed to fixup the   
   absolute minimum (a single short (two-byte)) backwards branch   
   instruction) I called it a day.   
      
   Terje   
      
   --   
   -    
   "almost all programming can be viewed as an exercise in caching"   
      
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