XPost: comp.lang.forth   
   From: nowhere@nospicedham.never.at   
      
   On 10.03.2020 06:09, JJ wrote:   
      
   >> In AMD64, the 4x instructions are *all* REX prefices. The 48   
   >> instruction is NOT a DEC reg instruction, it's a REX prefix.   
      
   > That's interresting. I didn't realize that there are two sets of opcode for   
   > `INC/DEC ` instructions in x86: `4x` and `FF Cx`. Is there any article   
   > about it? Why there's two set of them? And if one was added later, when was   
   > that?   
      
   There are lots of duplicate opcodes already from the start of it, Caused   
   by incomplete decoding, but it was cheaper to keep them ...   
      
   the classical LOAD vs STORE group:   
      
   8A C1 == 88 C8   
   8A c2 == 88 D0   
   ...   
   8B FE == 89 F7   
      
   and much more.   
      
   find the whole instruction set in sandpile.org.   
   __   
   wolfgang   
      
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