nitg-s: introduced unique perfect hasher

Signed-off-by: Alexandre Terrasa <alexandre@moz-code.org>

diff --git a/src/coloring.nit b/src/coloring.nit
index f1dcf87..e80ed87 100644 (file)
--- a/src/coloring.nit
+++ b/src/coloring.nit
@@ -716,6 +716,55 @@ private abstract class AbstractHasher[E: Object]
        fun super_elements(element: E, elements: Set[E]): Set[E] is abstract
 end
 
+# Perfect Hashing (PH)
+# T = type of holder
+# U = type of elements to hash
+private class PerfectHasher[T, U]
+
+       var operator: PHOperator
+
+       init(operator: PHOperator) do self.operator = operator
+
+       fun compute_masks(conflicts: Map[T, Set[U]], ids: Map[U, Int]): Map[T, Int] do
+               var masks = new HashMap[T, Int]
+               for mclasstype, mtypes in conflicts do
+                       masks[mclasstype] = compute_mask(mtypes, ids)
+               end
+               return masks
+       end
+
+       private fun compute_mask(mtypes: Set[U], ids: Map[U, Int]): Int do
+               var mask = 0
+               loop
+                       var used = new List[Int]
+                       for mtype in mtypes do
+                               var res = operator.op(mask, ids[mtype])
+                               if used.has(res) then
+                                       break
+                               else
+                                       used.add(res)
+                               end
+                       end
+                       if used.length == mtypes.length then break
+                       mask += 1
+               end
+               return mask
+       end
+
+       fun compute_hashes(elements: Map[T, Set[U]], ids: Map[U, Int], masks: Map[T, Int]): Map[T, Map[U, Int]] do
+               var hashes = new HashMap[T, Map[U, Int]]
+               for mclasstype, mtypes in elements do
+                       var mask = masks[mclasstype]
+                       var inhashes = new HashMap[U, Int]
+                       for mtype in mtypes do
+                               inhashes[mtype] = operator.op(mask, ids[mtype])
+                       end
+                       hashes[mclasstype] = inhashes
+               end
+               return hashes
+       end
+end
+
 # Abstract operator used for perfect hashing
 abstract class PHOperator
        fun op(mask: Int, id:Int): Int is abstract