From 48bd7b6a770cfdea8dd86ac85495036bf73f7f5c Mon Sep 17 00:00:00 2001
From: Gabriel Ozouf <gabriel.ozouf@numworks.com>
Date: Wed, 2 Dec 2020 15:19:49 +0100
Subject: [PATCH] [poincare/logarithm] Factor corner case log(x,0) and log(x,1)

---
 poincare/src/logarithm.cpp | 14 +++++---------
 1 file changed, 5 insertions(+), 9 deletions(-)

diff --git a/poincare/src/logarithm.cpp b/poincare/src/logarithm.cpp
index c38076685..a9faf8020 100644
--- a/poincare/src/logarithm.cpp
+++ b/poincare/src/logarithm.cpp
@@ -268,21 +268,17 @@ Expression Logarithm::simpleShallowReduce(ExpressionNode::ReductionContext reduc
   Expression c = childAtIndex(0);
   Expression b = childAtIndex(1);
 
-  // log(x,1)->Undefined
-  if (b.type() == ExpressionNode::Type::Rational && static_cast<Rational &>(b).isOne()) {
-    return replaceWithUndefinedInPlace();
-  }
-  // log(x,0) -> undef
-  if (b.type() == ExpressionNode::Type::Rational && static_cast<Rational &>(b).isZero()) {
+  // log(x,0) = log(x,1) = undef
+  if (b.type() == ExpressionNode::Type::Rational && (static_cast<Rational &>(b).isZero() || static_cast<Rational &>(b).isOne())) {
     return replaceWithUndefinedInPlace();
   }
   if (c.type() == ExpressionNode::Type::Rational) {
     const Rational r = static_cast<Rational &>(c);
-    // log(0, x) = undef
+    // log(0,x) = undef
     if (r.isZero()) {
       return replaceWithUndefinedInPlace();
     }
-    // log(1) = 0;
+    // log(1,x) = 0;
     if (r.isOne()) {
       Expression result = Rational::Builder(0);
       replaceWithInPlace(result);
@@ -290,7 +286,7 @@ Expression Logarithm::simpleShallowReduce(ExpressionNode::ReductionContext reduc
     }
   }
   bool infiniteArg = c.recursivelyMatches(Expression::IsInfinity, reductionContext.context());
-  // log(x,x)->1 with x != inf and log(inf,inf) = undef
+  // log(x,x) = 1 with x != inf, and log(inf,inf) = undef
   if (c.isIdenticalTo(b)) {
     Expression result = infiniteArg ? Undefined::Builder().convert<Expression>() : Rational::Builder(1).convert<Expression>();
     replaceWithInPlace(result);