#1017 Fix empty range handling of min/max_element (#1018)

Author: jonasgampigbmw

include/etl/algorithm.h

@@ -1449,16 +1449,20 @@ namespace etl
                         TCompare  compare)
   {
     TIterator minimum = begin;
-    ++begin;
 
-    while (begin != end)
+    if (begin != end)
     {
-      if (compare(*begin, *minimum))
+      ++begin;
+
+      while (begin != end)
       {
-        minimum = begin;
-      }
+        if (compare(*begin, *minimum))
+        {
+          minimum = begin;
+        }
 
-      ++begin;
+        ++begin;
+      }
     }
 
     return minimum;
@@ -1493,16 +1497,20 @@ namespace etl
                         TCompare  compare)
   {
     TIterator maximum = begin;
-    ++begin;
 
-    while (begin != end)
+    if (begin != end)
     {
-      if (!compare(*begin, *maximum))
+      ++begin;
+
+      while (begin != end)
       {
-        maximum = begin;
-      }
+        if (!compare(*begin, *maximum))
+        {
+          maximum = begin;
+        }
 
-      ++begin;
+        ++begin;
+      }
     }
 
     return maximum;
@@ -1538,21 +1546,25 @@ namespace etl
   {
     TIterator minimum = begin;
     TIterator maximum = begin;
-    ++begin;
 
-    while (begin != end)
+    if (begin != end)
     {
-      if (compare(*begin, *minimum))
-      {
-        minimum = begin;
-      }
+      ++begin;
 
-      if (compare(*maximum, *begin))
+      while (begin != end)
       {
-        maximum = begin;
-      }
+        if (compare(*begin, *minimum))
+        {
+          minimum = begin;
+        }
 
-      ++begin;
+        if (compare(*maximum, *begin))
+        {
+          maximum = begin;
+        }
+
+        ++begin;
+      }
     }
 
     return ETL_OR_STD::pair<TIterator, TIterator>(minimum, maximum);

test/test_algorithm.cpp

@@ -190,6 +190,15 @@ namespace
       CHECK_EQUAL(std::distance(data.begin(), expected), std::distance(data.begin(), result));
     }
 
+    //*************************************************************************
+    TEST(min_element_empty)
+    {
+      Vector dataEmpty;
+      Vector::iterator expected = std::min_element(dataEmpty.begin(), dataEmpty.end());
+      Vector::iterator result = etl::min_element(dataEmpty.begin(), dataEmpty.end());
+      CHECK_EQUAL(std::distance(dataEmpty.end(), expected), std::distance(dataEmpty.end(), result));
+    }
+
     //*************************************************************************
     TEST(max_element)
     {
@@ -206,6 +215,15 @@ namespace
       CHECK_EQUAL(std::distance(data.begin(), expected), std::distance(data.begin(), result));
     }
 
+    //*************************************************************************
+    TEST(max_element_empty)
+    {
+      Vector dataEmpty;
+      Vector::iterator expected = std::max_element(dataEmpty.begin(), dataEmpty.end());
+      Vector::iterator result = etl::max_element(dataEmpty.begin(), dataEmpty.end());
+      CHECK_EQUAL(std::distance(dataEmpty.end(), expected), std::distance(dataEmpty.end(), result));
+    }
+
     //*************************************************************************
     TEST(minmax_element)
     {
@@ -224,6 +242,16 @@ namespace
       CHECK_EQUAL(std::distance(data.begin(), expected.second), std::distance(data.begin(), result.second));
     }
 
+    //*************************************************************************
+    TEST(minmax_element_empty)
+    {
+      Vector dataEmpty;
+      std::pair<Vector::iterator, Vector::iterator> expected = std::minmax_element(dataEmpty.begin(), dataEmpty.end());
+      std::pair<Vector::iterator, Vector::iterator> result = etl::minmax_element(dataEmpty.begin(), dataEmpty.end());
+      CHECK_EQUAL(std::distance(dataEmpty.begin(), expected.first), std::distance(dataEmpty.begin(), result.first));
+      CHECK_EQUAL(std::distance(dataEmpty.begin(), expected.second), std::distance(dataEmpty.begin(), result.second));
+    }
+
     //*************************************************************************
     TEST(minmax)
     {