Fix integer overflow when composing nested affine views

solver/src/main/java/org/chocosolver/solver/variables/IViewFactory.java

@@ -32,6 +32,7 @@
  * A kind of factory relying on interface default implementation to allow (multiple) inheritance
  *
  * @author Jean-Guillaume FAGES
+ * @author Aditya Nikam <adityanikam9502@gmail.com>
  */
 public interface IViewFactory extends ISelf<Model> {
 
@@ -128,16 +129,21 @@ default IntVar intView(int a, IntVar var, int b) {
             }
             if (var instanceof IntAffineView) {
                 IntAffineView<?> view = (IntAffineView<?>) var;
-                int av = (view.p ? 1 : -1) * view.a * a;
-                int bv = a * view.b + b;
-                if (av == 1 && bv == 0) {
-                    return view.getVariable();
-                } else {
-                    return intView(av, view.getVariable(), bv);
+                // Compose in long: flattening can overflow int even when every
+                // value the composed expression can take is well within range.
+                long av = (view.p ? 1L : -1L) * view.a * a;
+                long bv = (long) a * view.b + b;
+                if (fitsInt(av) && fitsInt(bv)) {
+                    if (av == 1 && bv == 0) {
+                        return view.getVariable();
+                    } else {
+                        return intView((int) av, view.getVariable(), (int) bv);
+                    }
                 }
-            } else {
-                return new IntAffineView<>(var, a, b);
+                // Flattening would overflow, so stack a view on the view: its
+                // own coefficients are small enough to be applied one at a time.
             }
+            return new IntAffineView<>(var, a, b);
         } else {
             int lb, ub;
             if (a > 0) {
@@ -167,6 +173,14 @@ default IntVar intView(int a, IntVar var, int b) {
         }
     }
 
+    /**
+     * @param value a value computed in long arithmetic
+     * @return {@code true} if <i>value</i> can be stored in an int without loss
+     */
+    private static boolean fitsInt(long value) {
+        return value >= Integer.MIN_VALUE && value <= Integer.MAX_VALUE;
+    }
+
     /**
      * Create a view based on <i>var</i>, i.e. <i>view = |var|</i>
      *

solver/src/test/java/org/chocosolver/solver/variables/view/integer/IntAffineViewTest.java

@@ -27,6 +27,7 @@
  * <br/>
  *
  * @author Charles Prud'homme
+ * @author Aditya Nikam <adityanikam9502@gmail.com>
  * @since 06/10/2023
  */
 public class IntAffineViewTest {
@@ -229,4 +230,30 @@ public void testViewAndReification(boolean lcg) {
         assertEquals(m.getSolver().getSolutionCount(), 2);
         assertEquals(m.getSolver().getFailCount(), 2);
     }
+
+    @Test(groups = "1s", timeOut = 60000)
+    public void testNestedAffineViewOverflowKeepsSolution() {
+        Model m = new Model();
+        IntVar x = m.intVar("x", 46_341, 46_342, false);
+        // Flattening (x - 46341) * 46341 gives b = 46341 * -46341, which does
+        // not fit in an int, although the product itself is at most 46341.
+        IntVar result = x.sub(46_341).mul(46_341).intVar();
+        result.eq(0).post();
+        assertEquals(m.getSolver().solve(), true);
+        assertEquals(x.getValue(), 46_341);
+    }
+
+    @Test(groups = "1s", timeOut = 60000)
+    public void testNestedAffineViewOverflowRejectsInvalidSolution() {
+        Model m = new Model();
+        IntVar x = m.intVar("x", 46_341, 46_342, false);
+        IntVar result = x.sub(46_341).mul(46_341).intVar();
+        result.ne(0).post();
+        m.getSolver().setSearch(inputOrderLBSearch(x));
+        while (m.getSolver().solve()) {
+            assertEquals(x.getValue(), 46_342);
+            assertEquals(result.getValue(), 46_341);
+        }
+        assertEquals(m.getSolver().getSolutionCount(), 1);
+    }
 }