[GitHub] [incubator-mxnet] access2rohit commented on a change in pull request #19547: port & update pr16744 numpy gcd

[GitBox <gi...@apache.org>]

access2rohit commented on a change in pull request #19547:
URL: https://github.com/apache/incubator-mxnet/pull/19547#discussion_r569007106



##########
File path: tests/python/unittest/test_numpy_op.py
##########
@@ -3021,6 +3021,7 @@ def hybrid_forward(self, F, a, b, *args, **kwargs):
                       [[_np.float16, _np.float32, _np.float64], [_np.int32]]),
         'power': (1.0, 3.0, [lambda y, x1, x2: _np.power(x1, x2 - 1.0) * x2],
                              [lambda y, x1, x2: _np.power(x1, x2) * _np.log(x1)]),
+        'gcd': (-100, 100, [None], None, [[_np.int32]]),

Review comment:
       Can you tell me what is the test case here ? I didn't understand i/p and expected o/p 

##########
File path: src/common/cuda/rtc/forward_functions-inl.h
##########
@@ -541,6 +541,49 @@ lcm(const DType a, const DType2 b) {
   }
 }
 
+template <typename DType, typename DType2>
+__device__ inline typename type_util::mixed_type<DType, DType2>::type
+gcd(const DType a, const DType2 b) {
+  if (type_util::is_integral<DType>::value &&
+      type_util::is_integral<DType2>::value) {
+    DType A = a;
+    DType2 B = b;
+    // minus cases.
+    if (a < 0) {
+      A = -a;
+    }
+    if (b < 0) {
+      B = -b;
+    }
+    // handle zero-valued cases.
+    DType c;
+    if (a == 0 && b != 0) {
+      c = B;
+    } else if (b == 0 && a != 0) {
+      c = A;
+    } else if (a == 0 && b == 0) {
+      c = 0;
+    } else {
+      DType tmp;
+      if (A < B) {
+        tmp = A;
+        A = B;
+        B = tmp;
+      }
+      while (A % B != 0) {

Review comment:
       if the code executes in GPU it might be better to convert 
   `a%b = a - Floor(a/b) * b`
   this is a lot faster on GPU plus save the a%b in a variable instead of evaluating in the while loop 




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