LEA TagData,A3

  ; pack from
  MOVE.L #XPK_InBuf,(A3)+
  MOVE.L MemoryPtr,(A3)+
  MOVE.L #XPK_InLen,(A3)+
  MOVE.L FileSize,(A3)+

  ; pack to
  MOVE.L FileSize,D0
  ; word aligned
  ADDQ #2,D0
  AND.W #$FFFFFFFE,D0
  MOVE.L D0,D1
  ADD.L MemoryPtr,D0
  MOVE.L #XPK_OutBuf,(A3)+
  MOVE.L D0,(A3)+

  ; XPK needs lots of space to work when compressing
  ADD.L #XPK_MARGIN,D1
  ADD.L #XPK_MARGIN,D1
  MOVE.L #XPK_OutBufLen,(A3)+
  MOVE.L D1,(A3)+

  ; pack how
  LEA FASTPacker,A1
  MOVE.L #XPK_PackMethod,(A3)+
  MOVE.L A1,(A3)+

  ; how did it go
  LEA OutLen,A1
  MOVE.L #XPK_GetOutLen,(A3)+
  MOVE.L A1,(A3)+

  ; technically a TagItem is two ULONGs so be sure to have enough allocated for them
  ; XPKExamine was acting poorly when i wasn't providing enough ULONGs
  MOVE.L #TAG_DONE,(A3)+
  MOVE.L #TAG_DONE,(A3)+

  ; pack!
  MOVE.L XpkmasterBase,A6
  LEA TagData,A0
  CALLLIB _LVOXpkPack
  
  CNOP 0,4
TagData DS.L 32
MemoryPtr DS.L 1 ; place where compressed data is stored. long enough to handle buffer needed for compression and decompression
FileSize DS.L 1 ; the total bytes to compress
OutLen DS.L 1 ; how big is the compressed output
FASTPacker DC.B "FAST",0