Fix unary operator ceil/floor/trunc when data type is integer (#14251)

* fix integer precision loss due to casting to float

* add test

* update comment

src/operator/math_functions-inl.h

@@ -35,19 +35,24 @@ namespace op {
 namespace math {
 
 // Wrappers for math.h unary and binary functions
-// - For DType != double: math::name(a) does computation in float
+// - For DType == float: math::name(a) does computation in float
 //   and returns float
-// - For DType == double: math::name(a) does computation in double
+// - For DType == double or DType == integer: math::name(a) does computation in double
 //   and returns double
 
 #define MXNET_UNARY_MATH_FUNC(name) \
-template<typename DType> MSHADOW_XINLINE \
-float name(DType a) { \
-  return ::name##f(static_cast<float>(a)); \
+MSHADOW_XINLINE \
+float name(float a) { \
+  return ::name##f(a); \
 } \
 MSHADOW_XINLINE \
 double name(double a) { \
   return ::name(a); \
+} \
+template<typename DType> MSHADOW_XINLINE \
+typename std::enable_if<std::is_integral<DType>::value, double>::type \
+name(DType a) { \
+  return ::name(static_cast<double>(a)); \
 }
 
 #define MXNET_BINARY_MATH_FUNC(name) \

tests/python/unittest/test_ndarray.py

@@ -1952,6 +1952,25 @@ def test_op(op, num_inputs, mutated_inputs, **kwargs):
             {'rescale_grad': 0.1, 'lr': 0.01, 'wd': 1e-3})
 
 
+def test_large_int_rounding():
+    large_integer = 50000001
+
+    a = mx.nd.array([large_integer], dtype='int32')
+    assert np.all(a == large_integer)
+
+    a = mx.nd.array([large_integer], dtype='int32').floor()
+    assert np.all(a == large_integer)
+
+    a = mx.nd.array([large_integer], dtype='int32').round()
+    assert np.all(a == large_integer)
+
+    a = mx.nd.array([large_integer], dtype='int32').ceil()
+    assert np.all(a == large_integer)
+
+    a = mx.nd.array([large_integer], dtype='int32').trunc()
+    assert np.all(a == large_integer)
+
+
 if __name__ == '__main__':
     import nose
     nose.runmodule()