From 5b7b50f206089c52daf6ab7d59b1b9829e5a6bda Mon Sep 17 00:00:00 2001
From: Jean-Guillaume Fages <jg.fages@cosling.com>
Date: Fri, 21 Jul 2023 17:55:18 +0200
Subject: [PATCH] use square when possible and stronger filtering

practical interest to be confirmed by experiments
---
 .../constraints/IIntConstraintFactory.java    |  4 +-
 .../solver/constraints/binary/PropSquare.java | 44 ++++++++++---------
 2 files changed, 26 insertions(+), 22 deletions(-)

diff --git a/solver/src/main/java/org/chocosolver/solver/constraints/IIntConstraintFactory.java b/solver/src/main/java/org/chocosolver/solver/constraints/IIntConstraintFactory.java
index e857536d7b..fc844e9b25 100644
--- a/solver/src/main/java/org/chocosolver/solver/constraints/IIntConstraintFactory.java
+++ b/solver/src/main/java/org/chocosolver/solver/constraints/IIntConstraintFactory.java
@@ -736,7 +736,9 @@ default Constraint mod(IntVar X, IntVar Y, IntVar Z) {
      */
     @SuppressWarnings("SuspiciousNameCombination")
     default Constraint times(IntVar X, IntVar Y, IntVar Z) {
-        if (Y.isInstantiated()) {
+        if (X == Y) {
+            return square(Z, X);
+        } else if (Y.isInstantiated()) {
             return times(X, Y.getValue(), Z);
         } else if (X.isInstantiated()) {
             return times(Y, X.getValue(), Z);
diff --git a/solver/src/main/java/org/chocosolver/solver/constraints/binary/PropSquare.java b/solver/src/main/java/org/chocosolver/solver/constraints/binary/PropSquare.java
index 1daf550ad1..00aa828474 100644
--- a/solver/src/main/java/org/chocosolver/solver/constraints/binary/PropSquare.java
+++ b/solver/src/main/java/org/chocosolver/solver/constraints/binary/PropSquare.java
@@ -117,7 +117,6 @@ protected void updateLowerBoundofX() throws ContradictionException {
 
     protected void updateUpperBoundofX() throws ContradictionException {
         vars[0].updateUpperBound(Math.max(sqr(vars[1].getLB()), sqr(vars[1].getUB())), this);
-
     }
 
     protected boolean updateHolesinX() throws ContradictionException {
@@ -158,7 +157,11 @@ protected boolean updateHolesinX() throws ContradictionException {
     }
 
     protected boolean updateLowerBoundofY() throws ContradictionException {
-        return vars[1].updateLowerBound(-ceil_sqrt(vars[0].getUB()), this);
+        if (vars[1].getLB() >= 0) {
+            return vars[1].updateLowerBound(ceil_sqrt(vars[0].getLB()), this);
+        } else {
+            return vars[1].updateLowerBound(-floor_sqrt(vars[0].getUB()), this);
+        }
     }
 
     protected boolean updateUpperBoundofY() throws ContradictionException {
@@ -166,8 +169,19 @@ protected boolean updateUpperBoundofY() throws ContradictionException {
     }
 
     protected boolean updateHolesinY() throws ContradictionException {
-        // remove intervals to deal with consecutive value removal and upper bound modification
-        if (bothEnum) {
+        if (vars[0].isInstantiatedTo(0)) {
+            return vars[1].instantiateTo(0, this);
+        }
+        boolean impact = false;
+        // remove interval around 0 based on X LB
+        if (vars[1].hasEnumeratedDomain()) {
+            int val = ceil_sqrt(vars[0].getLB()) - 1;
+            if (val >= 0) {
+                impact = vars[1].removeInterval(-val, val, this);
+            }
+        }
+        // remove values based on X holes
+        if (bothEnum && hasHoles(vars[0])) {
             int ub = vars[1].getUB();
             vrms.clear();
             vrms.setOffset(vars[1].getLB());
@@ -176,24 +190,12 @@ protected boolean updateHolesinY() throws ContradictionException {
                     vrms.add(value);
                 }
             }
-            return vars[1].removeValues(vrms, this);
-        } else if (vars[1].hasEnumeratedDomain()) {
-            int lb = vars[1].getLB();
-            int ub = vars[1].getUB();
-            while (!vars[0].contains(sqr(lb))) {
-                lb = vars[1].nextValue(lb);
-                if (lb > ub) break;
-            }
-            boolean filter = vars[1].updateLowerBound(lb, this);
-
-            while (!vars[0].contains(sqr(ub))) {
-                ub = vars[1].nextValue(ub);
-                if (ub < lb) break;
-            }
-            return filter | vars[1].updateUpperBound(ub, this);
+            impact |= vars[1].removeValues(vrms, this);
         }
-        return false;
+        return impact;
     }
 
-
+    private boolean hasHoles(IntVar var) {
+        return (var.getUB() - var.getLB() + 1) > var.getDomainSize();
+    }
 }