A quick glance at the source suggests that they are flags/values indicating/used for:

• refin
  reflect bitwise (mirror) the input before processing the message
• refout
  reflect bitwise (mirror) the processed data before returning (hmmm, unless refin is set...)
• xorout
  the output is XORed with this value prior to returning it
• init
  is the initial crc value

Update: (added init explanation) I suggest you take a closer look at the %_typedef hash!

Edit: removed doubt-indicating questionmarks.

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