From a2f435bed347b43a9efc2bf239a71143d4d07bfd Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?L=C3=A9a=20Saviot?= <lea.saviot@numworks.com>
Date: Fri, 23 Aug 2019 16:53:50 +0200
Subject: [PATCH] [poincare/inv_norm] Don't simplify if variance is not checked
 to be >0

---
 poincare/src/inv_norm.cpp        | 35 ++++++++++++++++++++++++++++----
 poincare/test/simplification.cpp |  3 +++
 2 files changed, 34 insertions(+), 4 deletions(-)

diff --git a/poincare/src/inv_norm.cpp b/poincare/src/inv_norm.cpp
index 447645efd..95370a0c9 100644
--- a/poincare/src/inv_norm.cpp
+++ b/poincare/src/inv_norm.cpp
@@ -50,16 +50,43 @@ Expression InvNorm::shallowReduce(ExpressionNode::ReductionContext reductionCont
   }
   Expression c0 = childAtIndex(0);
   Expression c1 = childAtIndex(1);
+  Expression c2 = childAtIndex(2);
+  Context * context = reductionContext.context();
+
+  if (c0.deepIsMatrix(context) || c1.deepIsMatrix(context) || c2.deepIsMatrix(context)) {
+    return replaceWithUndefinedInPlace();
+  }
+
+  if (!c1.isReal(context) || !c2.isReal(context)) {
+    // If we cannot check that mu and variance are real, return
+    return *this;
+  }
+
   {
-    Context * context = reductionContext.context();
-    Expression c2 = childAtIndex(2);
-    if (c0.deepIsMatrix(context) || c1.deepIsMatrix(context) || c2.deepIsMatrix(context)) {
+    ExpressionNode::Sign s = c2.sign(context);
+    if (s == ExpressionNode::Sign::Negative) {
       return replaceWithUndefinedInPlace();
     }
-    if (c0.type() != ExpressionNode::Type::Rational) {
+    // If we cannot check that the variance is positive, return
+    if (s != ExpressionNode::Sign::Positive) {
       return *this;
     }
   }
+
+  // If we cannot check that the variance is not null, return
+  if (c2.type() != ExpressionNode::Type::Rational) {
+    return *this;
+  }
+  {
+    Rational r2 = static_cast<Rational &>(c2);
+    if (r2.isZero()) {
+      return replaceWithUndefinedInPlace();
+    }
+  }
+
+  if (c0.type() != ExpressionNode::Type::Rational) {
+    return *this;
+  }
   // Undef if x < 0 or x > 1
   Rational r0 = static_cast<Rational &>(c0);
   if (r0.isNegative()) {
diff --git a/poincare/test/simplification.cpp b/poincare/test/simplification.cpp
index e7dc628a4..cec1614a6 100644
--- a/poincare/test/simplification.cpp
+++ b/poincare/test/simplification.cpp
@@ -1066,4 +1066,7 @@ QUIZ_CASE(poincare_probabolity) {
   assert_parsed_expression_simplify_to("invnorm(0.5,2,3)", "2");
   assert_parsed_expression_simplify_to("invnorm(1,2,3)", "inf");
   assert_parsed_expression_simplify_to("invnorm(1.3,2,3)", "undef");
+  assert_parsed_expression_simplify_to("invnorm(3/4,2,random())", "invnorm(3/4,2,random())"); // random can be 0
+  assert_parsed_expression_simplify_to("invnorm(0.5,2,0)", Undefined::Name());
+  assert_parsed_expression_simplify_to("invnorm(0.5,2,-1)", Undefined::Name());
 }