[MXNET-1422] Fix wrong results of min([inf, inf]) and max([-inf,-inf])

3rdparty/mshadow/mshadow/base.h

@@ -645,6 +645,25 @@ MSHADOW_XINLINE int64_t MinValue<int64_t>(void) {
   return LLONG_MIN;
 }
 
+/*!
+ * \brief negative infinity of certain types
+ * \tparam DType data type
+ */
+template<typename DType>
+MSHADOW_XINLINE DType NegInfValue(void) {
+  return MinValue<DType>();
+}
+/*! \brief negative infinity value of float */
+template<>
+MSHADOW_XINLINE float NegInfValue<float>(void) {
+  return -HUGE_VALF;
+}
+/*! \brief negative infinity value of double */
+template<>
+MSHADOW_XINLINE double NegInfValue<double>(void) {
+  return -HUGE_VAL;
+}
+
 /*!
  * \brief maximum value of certain types
  * \tparam DType data type
@@ -686,6 +705,26 @@ template<>
 MSHADOW_XINLINE int64_t MaxValue<int64_t>(void) {
   return LLONG_MAX;
 }
+
+/*!
+ * \brief positive infinity of certain types
+ * \tparam DType data type
+ */
+template<typename DType>
+MSHADOW_XINLINE DType PosInfValue(void) {
+  return MaxValue<DType>();
+}
+/*! \brief positive infinity value of float */
+template<>
+MSHADOW_XINLINE float PosInfValue<float>(void) {
+  return HUGE_VALF;
+}
+/*! \brief positive infinity value of double */
+template<>
+MSHADOW_XINLINE double PosInfValue<double>(void) {
+  return HUGE_VAL;
+}
+
 }  // namespace limits
 
 /*! \brief sum reducer */
@@ -793,7 +832,7 @@ struct maximum {
    */
   template<typename DType>
   MSHADOW_XINLINE static void SetInitValue(DType &initv) { // NOLINT(*)
-    initv = limits::MinValue<DType>();
+    initv = limits::NegInfValue<DType>();
   }
   /*!
    *\brief set the initial value during reduction
@@ -849,7 +888,7 @@ struct minimum {
    */
   template<typename DType>
   MSHADOW_XINLINE static void SetInitValue(DType &initv) { // NOLINT(*)
-    initv = limits::MaxValue<DType>();
+    initv = limits::PosInfValue<DType>();
   }
   /*!
    *\brief set the initial value during reduction

tests/python/unittest/test_operator.py

@@ -9252,6 +9252,23 @@ def test_sample_normal_default_shape():
     assert s.shape == (1, 1)
 
 
+def test_min_max_inf():
+    dtypes = [np.float32, np.double]
+    elem_list = [-1, 1, 0, np.inf, -np.inf]
+
+    for dtype in dtypes:
+        for a in elem_list:
+            for b in elem_list:
+                data_np = np.array([a, b], dtype=dtype)
+                data_mx = mx.nd.array(data_np, dtype=dtype)
+
+                min_data_np, max_data_np = data_np.min(), data_np.max()
+                min_data_mx, max_data_mx = data_mx.min(), data_mx.max()
+
+                assert_array_equal(min_data_np, min_data_mx.asnumpy())
+                assert_array_equal(max_data_np, max_data_mx.asnumpy())
+
+
 if __name__ == '__main__':
     import nose
     nose.runmodule()