(* field-def.sml
 *
 * COPYRIGHT (c) 2010 The Diderot Project (http://diderot.cs.uchicago.edu)
 * All rights reserved.
 *)

structure FieldDef =
  struct

  (* the static definition of a field value *)
    datatype field_def
      = CONV of ImageInfo.info * Kernel.kernel	(* convolution *)
      | DIFF of int * field_def			(* k levels of differentiation *)
      | NEG of field_def
      | SUM of field_def * field_def
(* scaling too? *)

  (* normalize a field definition by pushing the DIFF operators to the
   * leaves
   *)
    fun normalize fld = let
	  fun norm fld = (case fld
		 of CONV _ => fld
		  | DIFF(k, fld) => diff (k, fld)
		  | NEG fld => NEG(norm fld)
		  | SUM(fld1, fld2) => SUM(norm fld1, norm fld2)
		(* end case *))
	  and diff (k, fld) = (case fld
		 of CONV _ => DIFF(k, fld)
		  | DIFF(k', fld) => diff (k+k', fld)
		  | NEG fld => NEG(diff(k, fld))
		  | SUM(fld1, fld2) => SUM(diff(k, fld1), diff(k, fld2))
		(* end case *))
	  in
	    norm fld
	  end

  (* equality test for field definitions *)
    fun same (CONV(img1, kern1), CONV(img2, kern2)) =
	  ImageInfo.same(img1, img2) andalso Kernel.same(kern1, kern2)
      | same (DIFF(k1, fld1), DIFF(k2, fld2)) =
	  (k1 = k2) andalso same(fld1, fld2)
      | same (NEG fld1, NEG fld2) = same(fld1, fld2)
      | same (SUM(fld11, fld12), SUM(fld21, fld22)) = 
	  same(fld11, fld21) andalso same(fld12, fld22)

  (* hash value *)
    fun hash (CONV(img, kern)) = 0w3 * ImageInfo.hash img + Kernel.hash kern
      | hash (DIFF(k, fld)) = Word.fromInt k * 0w17 + hash fld
      | hash (NEG fld) = 0w3 * hash fld + 0w11
      | hash (SUM(fld1, fld2)) = 0w7 * hash fld1 + hash fld2

    fun toString (CONV(img, kern)) =
	  concat["<", ImageInfo.toString img, "*", Kernel.name kern, ">"]
      | toString (DIFF(k, fld)) =
	  concat["(D", Int.toString k, " ", toString fld, ")"]
      | toString (NEG fld) = "-" ^ toString fld
      | toString (SUM(fld1, NEG fld2)) =
	  concat["(", toString fld1, "-", toString fld2, ")"]
      | toString (SUM(fld1, fld2)) =
	  concat["(", toString fld1, "+", toString fld2, ")"]

  end

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	<div class="error">does not end with &lt;/html&gt; tag</div>
	<div class="error">does not end with &lt;/body&gt; tag</div>
	<div class="info">The output has ended thus: ]
      | toString (SUM(fld1, fld2)) =
	  concat[&quot;(&quot;, toString fld1, &quot;+&quot;, toString fld2, &quot;)&quot;]

  end</div>
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