From: james.harris.1@nospicedham.gmail.com   
      
   On 30/06/2017 07:41, James Harris wrote:   
   > On 29/06/2017 23:40, Rod Pemberton wrote:   
      
   ...   
      
   >> When "if (x == MIGHT)", the XOR result is 0x20, meaning that the two   
   >> characters are either an upper- and lower-case alphabetic which are the   
   >> same when lower-cased, or they're two different graphics characters   
   >> 0x20 apart.   
   >   
   > That's far from obvious but I have to say that for ASCII it seems to be   
   > correct. And it may work for EBCDIC too (with an XOR of 0x40).   
      
   Maybe that suggests a fast way of recognising a letter in ASCII without   
   using a lookup table:   
      
      or al, 'a' ^ 'A'   
      sub al, 'a'   
      cmp al, 'z' - 'a'   
      ja is_not_alphabetic   
      
      
   --   
   James Harris   
      
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