Add support for Boolean argmin/argmax to FlatZinc, and perform offset calculation natively rather than through MiniZinc constraints

Author: guidotack

changelog.in

@@ -68,6 +68,21 @@ Date: 2019-??-??
 [DESCRIPTION]
 Let's see.
 
+[ENTRY]
+Module: flatzinc
+What:   new
+Rank:   minor
+[DESCRIPTION]
+Support minimum_arg_bool and maximum_arg_bool constraints.
+
+[ENTRY]
+Module: flatzinc
+What:   change
+Rank:   minor
+[DESCRIPTION]
+Use native offset calculation instead of additional constraints
+for argmin/argmax constraints.
+
 [ENTRY]
 Module: int
 What:   new

gecode/flatzinc/mznlib/arg_max_bool.mzn

@@ -0,0 +1,4 @@
+predicate gecode_maximum_arg_bool_offset(array[int] of var bool: x, int: offset, var int: i);
+
+predicate maximum_arg_bool(array[int] of var bool: x, var int: i) =
+  gecode_maximum_arg_bool_offset(x,min(index_set(x)),i);

gecode/flatzinc/mznlib/arg_max_int.mzn

@@ -1,4 +1,4 @@
-predicate gecode_maximum_arg_int(array[int] of var int: x, var int: i);
+predicate gecode_maximum_arg_int_offset(array[int] of var int: x, int: offset, var int: i);
 
 predicate maximum_arg_int(array[int] of var int: x, var int: i) =
-  gecode_maximum_arg_int(x,(i-min(index_set(x)))::domain);
+  gecode_maximum_arg_int_offset(x,min(index_set(x)),i);

gecode/flatzinc/mznlib/arg_min_bool.mzn

@@ -0,0 +1,4 @@
+predicate gecode_minimum_arg_bool_offset(array[int] of var bool: x, int: offset, var int: i);
+
+predicate minimum_arg_bool(array[int] of var bool: x, var int: i) =
+  gecode_minimum_arg_bool_offset(x,min(index_set(x)),i);

gecode/flatzinc/mznlib/arg_min_int.mzn

@@ -1,4 +1,4 @@
-predicate gecode_minimum_arg_int(array[int] of var int: x, var int: i);
+predicate gecode_minimum_arg_int_offset(array[int] of var int: x, int: offset, var int: i);
 
 predicate minimum_arg_int(array[int] of var int: x, var int: i) =
-  gecode_minimum_arg_int(x,(i-min(index_set(x)))::domain);
+  gecode_minimum_arg_int_offset(x,min(index_set(x)),i);

gecode/flatzinc/registry.cpp

@@ -1022,12 +1022,26 @@ namespace Gecode { namespace FlatZinc {
 
     void p_minimum_arg(FlatZincSpace& s, const ConExpr& ce, AST::Node* ann) {
       IntVarArgs iv = s.arg2intvarargs(ce[0]);
-      argmin(s, iv, s.arg2IntVar(ce[1]), true, s.ann2ipl(ann));
+      int offset = ce[1]->getInt();
+      argmin(s, iv, offset, s.arg2IntVar(ce[2]), true, s.ann2ipl(ann));
     }
 
     void p_maximum_arg(FlatZincSpace& s, const ConExpr& ce, AST::Node* ann) {
       IntVarArgs iv = s.arg2intvarargs(ce[0]);
-      argmax(s, iv, s.arg2IntVar(ce[1]), true, s.ann2ipl(ann));
+      int offset = ce[1]->getInt();
+      argmax(s, iv, offset, s.arg2IntVar(ce[2]), true, s.ann2ipl(ann));
+    }
+
+    void p_minimum_arg_bool(FlatZincSpace& s, const ConExpr& ce, AST::Node* ann) {
+      BoolVarArgs bv = s.arg2boolvarargs(ce[0]);
+      int offset = ce[1]->getInt();
+      argmin(s, bv, offset, s.arg2IntVar(ce[2]), true, s.ann2ipl(ann));
+    }
+
+    void p_maximum_arg_bool(FlatZincSpace& s, const ConExpr& ce, AST::Node* ann) {
+      BoolVarArgs bv = s.arg2boolvarargs(ce[0]);
+      int offset = ce[1]->getInt();      
+      argmax(s, bv, offset, s.arg2IntVar(ce[2]), true, s.ann2ipl(ann));
     }
 
     void p_regular(FlatZincSpace& s, const ConExpr& ce, AST::Node* ann) {
@@ -1562,8 +1576,10 @@ namespace Gecode { namespace FlatZinc {
           &p_global_cardinality_low_up_closed);
         registry().add("array_int_minimum", &p_minimum);
         registry().add("array_int_maximum", &p_maximum);
-        registry().add("gecode_minimum_arg_int", &p_minimum_arg);
-        registry().add("gecode_maximum_arg_int", &p_maximum_arg);
+        registry().add("gecode_minimum_arg_int_offset", &p_minimum_arg);
+        registry().add("gecode_maximum_arg_int_offset", &p_maximum_arg);
+        registry().add("gecode_minimum_arg_bool_offset", &p_minimum_arg_bool);
+        registry().add("gecode_maximum_arg_bool_offset", &p_maximum_arg_bool);
         registry().add("array_int_maximum", &p_maximum);
         registry().add("gecode_regular", &p_regular);
         registry().add("sort", &p_sort);