From 0c040a7db6f0fa35f4127f019e3cfc8eec0b59b3 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?L=C3=A9a=20Saviot?= <lea.saviot@numworks.com>
Date: Wed, 3 Jun 2020 11:39:37 +0200
Subject: [PATCH] [poincare/power] Fix infinite loop in reduction

Fix the broken simplification test 1/identity(2)^500
---
 poincare/src/power.cpp | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/poincare/src/power.cpp b/poincare/src/power.cpp
index 4ab6fb07f..525e9a89f 100644
--- a/poincare/src/power.cpp
+++ b/poincare/src/power.cpp
@@ -439,6 +439,12 @@ Expression Power::shallowReduce(ExpressionNode::ReductionContext reductionContex
       if (exponent.isNegative()) {
         index.setSign(ExpressionNode::Sign::Positive, reductionContext);
         Expression reducedPositiveExponentMatrix = shallowReduce(reductionContext);
+        if (reducedPositiveExponentMatrix.type() == ExpressionNode::Type::Power) {
+          /* The shallowReduce did not work, stop here so we do not get in an
+           * infinite loop. */
+          static_cast<Power &>(reducedPositiveExponentMatrix).childAtIndex(1).setSign(ExpressionNode::Sign::Negative, reductionContext);
+          return reducedPositiveExponentMatrix;
+        }
         Expression dummyExpression = Undefined::Builder();
         MatrixInverse inv = MatrixInverse::Builder(dummyExpression);
         reducedPositiveExponentMatrix.replaceWithInPlace(inv);