--- /dev/null
+! Copyright (C) 2011 John Benediktsson
+! See http://factorcode.org/license.txt for BSD license
+
+USING: accessors alien.c-types classes.struct
+classes.struct.private kernel locals math sequences slots
+words ;
+
+IN: classes.struct.packed
+
+<PRIVATE
+
+CONSTANT: ALIGNMENT 1
+
+GENERIC: compute-packed-offset ( offset class -- offset' )
+
+M: struct-slot-spec compute-packed-offset
+ [ ALIGNMENT 8 * align ] dip
+ [ [ 8 /i ] dip offset<< ] [ type>> heap-size 8 * + ] 2bi ;
+
+M: struct-bit-slot-spec compute-packed-offset
+ [ offset<< ] [ bits>> + ] 2bi ;
+
+: compute-packed-offsets ( slots -- size )
+ 0 [ compute-packed-offset ] reduce 8 align 8 /i ;
+
+:: (define-packed-class) ( class slots offsets-quot -- )
+ slots empty? [ struct-must-have-slots ] when
+ class redefine-struct-tuple-class
+ slots make-slots dup check-struct-slots :> slot-specs
+ slot-specs offsets-quot call :> unaligned-size
+ ALIGNMENT :> alignment
+ unaligned-size :> size
+
+ class slot-specs size alignment c-type-for-class :> c-type
+
+ c-type class typedef
+ class slot-specs define-accessors
+ class size "struct-size" set-word-prop
+ class dup make-struct-prototype "prototype" set-word-prop
+ class (struct-methods) ; inline
+
+: define-packed-struct-class ( class slots -- )
+ [ compute-packed-offsets ] (define-packed-class) ;
+
+PRIVATE>
+
+SYNTAX: PACKED-STRUCT:
+ parse-struct-definition define-packed-struct-class ;
+
+