From ff3dc8ac73ec344c1595b7151e6f1a3fcdb2a731 Mon Sep 17 00:00:00 2001
From: ShenLiang <shenliang03@baidu.com>
Date: Fri, 4 Sep 2020 13:15:26 +0800
Subject: [PATCH] fix the remainder (#26995)

---
 .../elementwise/elementwise_mod_op.h          | 40 +++++++++++++++++--
 .../unittests/test_elementwise_mod_op.py      |  8 ++++
 2 files changed, 44 insertions(+), 4 deletions(-)

diff --git a/paddle/fluid/operators/elementwise/elementwise_mod_op.h b/paddle/fluid/operators/elementwise/elementwise_mod_op.h
index 47bd6af0b95..87e940e2ed6 100644
--- a/paddle/fluid/operators/elementwise/elementwise_mod_op.h
+++ b/paddle/fluid/operators/elementwise/elementwise_mod_op.h
@@ -31,6 +31,15 @@ struct ModFunctor {
   }
 };
 
+template <typename T>
+struct InverseModFunctor {
+  inline HOSTDEVICE T operator()(T a, T b) const {
+    T res = b % a;
+    if ((res != 0) && ((res < 0) != (a < 0))) res += a;
+    return res;
+  }
+};
+
 template <typename T>
 struct ModFunctorFP {
   inline HOSTDEVICE T operator()(T a, T b) const {
@@ -40,13 +49,29 @@ struct ModFunctorFP {
   }
 };
 
+template <typename T>
+struct InverseModFunctorFP {
+  inline HOSTDEVICE T operator()(T a, T b) const {
+    T res = fmod(b, a);
+    if ((res != 0) && ((a < 0) != (res < 0))) res += a;
+    return res;
+  }
+};
+
 template <typename DeviceContext, typename T>
 void elementwise_mod(const framework::ExecutionContext &ctx,
                      const framework::Tensor *x, const framework::Tensor *y,
                      framework::Tensor *z) {
   int axis = ctx.Attr<int>("axis");
-  ElementwiseComputeEx<ModFunctor<T>, DeviceContext, T>(ctx, x, y, axis,
-                                                        ModFunctor<T>(), z);
+  auto x_dims = x->dims();
+  auto y_dims = y->dims();
+  if (x_dims.size() >= y_dims.size()) {
+    ElementwiseComputeEx<ModFunctor<T>, DeviceContext, T>(ctx, x, y, axis,
+                                                          ModFunctor<T>(), z);
+  } else {
+    ElementwiseComputeEx<InverseModFunctor<T>, DeviceContext, T>(
+        ctx, x, y, axis, InverseModFunctor<T>(), z);
+  }
 }
 
 template <typename DeviceContext, typename T>
@@ -54,8 +79,15 @@ void elementwise_mod_fp(const framework::ExecutionContext &ctx,
                         const framework::Tensor *x, const framework::Tensor *y,
                         framework::Tensor *z) {
   int axis = ctx.Attr<int>("axis");
-  ElementwiseComputeEx<ModFunctorFP<T>, DeviceContext, T>(ctx, x, y, axis,
-                                                          ModFunctorFP<T>(), z);
+  auto x_dims = x->dims();
+  auto y_dims = y->dims();
+  if (x_dims.size() >= y_dims.size()) {
+    ElementwiseComputeEx<ModFunctorFP<T>, DeviceContext, T>(
+        ctx, x, y, axis, ModFunctorFP<T>(), z);
+  } else {
+    ElementwiseComputeEx<InverseModFunctorFP<T>, DeviceContext, T>(
+        ctx, x, y, axis, InverseModFunctorFP<T>(), z);
+  }
 }
 
 template <typename DeviceContext, typename T>
diff --git a/python/paddle/fluid/tests/unittests/test_elementwise_mod_op.py b/python/paddle/fluid/tests/unittests/test_elementwise_mod_op.py
index f5d8b4f704d..cab6160d761 100644
--- a/python/paddle/fluid/tests/unittests/test_elementwise_mod_op.py
+++ b/python/paddle/fluid/tests/unittests/test_elementwise_mod_op.py
@@ -220,6 +220,14 @@ class TestRemainderAPI(unittest.TestCase):
                 z_expected = np.array([0, 1, 1, -1])
                 self.assertEqual(np.allclose(z_expected, z.numpy()), True)
 
+                np_x = np.array([-3, 3])
+                np_y = np.array([[2, 3], [-2, -1]])
+                x = paddle.to_tensor(np_x, dtype="int64")
+                y = paddle.to_tensor(np_y, dtype="int64")
+                z = x % y
+                z_expected = np.array([[1, 0], [-1, 0]])
+                self.assertEqual(np.allclose(z_expected, z.numpy()), True)
+
 
 if __name__ == '__main__':
     unittest.main()
-- 
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