Non-zero result of Vector3.Cross with parallel vectors (#119438)

* Non-zero result of Vector3.Cross with parallel vectors

* fix first remark

* improve codegen

Co-authored-by: Tanner Gooding <tagoo@outlook.com>

---------

Co-authored-by: Tanner Gooding <tagoo@outlook.com>

Author: pedrobsaila

src/libraries/System.Numerics.Vectors/tests/Vector3Tests.cs

@@ -207,6 +207,17 @@ public void Vector3CrossTest1()
             Assert.True(MathHelper.Equal(expected, actual), "Vector3f.Cross did not return the expected value.");
         }
 
+        // A test for Cross (Vector3f, Vector3f)
+        // Cross test of the same parallel vector
+        [Fact]
+        public void Vector3CrossSameParallelVectors()
+        {
+            var v = new Vector3(-1, 1, 0);
+            var n = Vector3.Normalize(v);
+            var actual = Vector3.Cross(n, n);
+            Assert.Equal(Vector3.Zero, actual);
+        }
+
         // A test for Distance (Vector3f, Vector3f)
         [Fact]
         public void Vector3DistanceTest()

src/libraries/System.Private.CoreLib/src/System/Numerics/Vector3.cs

@@ -471,13 +471,10 @@ public static Vector3 Cross(Vector3 vector1, Vector3 vector2)
             Vector128<float> v1 = vector1.AsVector128Unsafe();
             Vector128<float> v2 = vector2.AsVector128Unsafe();
 
-            Vector128<float> temp = Vector128.Shuffle(v1, Vector128.Create(1, 2, 0, 0)) * Vector128.Shuffle(v2, Vector128.Create(2, 0, 1, 0));
+            Vector128<float> temp1 = Vector128.Shuffle(v1, Vector128.Create(1, 2, 0, 0)) * Vector128.Shuffle(v2, Vector128.Create(2, 0, 1, 0));
+            Vector128<float> temp2 = Vector128.Shuffle(v1, Vector128.Create(2, 0, 1, 0)) * Vector128.Shuffle(v2, Vector128.Create(1, 2, 0, 0));
 
-            return Vector128.MultiplyAddEstimate(
-                -Vector128.Shuffle(v1, Vector128.Create(2, 0, 1, 0)),
-                 Vector128.Shuffle(v2, Vector128.Create(1, 2, 0, 0)),
-                 temp
-            ).AsVector3();
+            return (temp1 - temp2).AsVector3();
         }
 
         /// <inheritdoc cref="Vector4.DegreesToRadians(Vector4)" />