Great! Glad that we agree that ($B,$A)=($A,$B) is FAR superior the XOR trick! Clarity is an important aspect of software engineering.

XOR is fundamental to data encryption and error correction codes. But for the most part, you won't need to use this in your normal code!!

This is a bit off topic as this is 'C' Code, but just to show you another tricky way of using XOR in a low level sub. This is basically "modem code" as it looks like the gibberish that would result from an unsync'd modem!!

Low level C has stuff like this, but almost no Perl code should have it! Heck the raw assembly code is easier to understand this this critter below, but this idiomatic good C code. enjoy.

/* flip all bits except between range defined 
   by startBit and numBits to left*/
/* bit numbering like: 7 6 5 4 3 2 1 0 */

inline unsigned short flipNotInRange (unsigned short in, int startBit,
+ int numBits)
{
  unsigned short result;
  
  result =(~in) ^ (~((unsigned short) ~0<<numBits )<< startBit);
  return result;
}
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