[GitHub] larroy commented on a change in pull request #13857: float32 -> float16 cast consistency across implementations

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

larroy commented on a change in pull request #13857: float32 -> float16 cast consistency across implementations
URL: https://github.com/apache/incubator-mxnet/pull/13857#discussion_r248657815
 
 

 ##########
 File path: tests/python/unittest/test_operator.py
 ##########
 @@ -3994,6 +3994,44 @@ def test_cast():
             assert_almost_equal(exe.grad_arrays[0].asnumpy(), X.astype(dsttype).astype(srctype), rtol=1e-3, atol=1e-5)
 
 
+# Test requires all platforms to round float32->float16 with same round-to-nearest-even policy.
+@with_seed()
+def test_cast_float32_to_float16():
+    fp16_fraction_bits = 10
+    fp32_fraction_bits = 23
+    fp32_exp_min = -126
+    fp32_exp_max = 127
+    # generate test cases in the vicinity of representable float16 mantissas
+    # and mid-way between them, but over the full range of float32 exponents.
+    def get_data():
+        for sign_bit in [0, 1]:
+            for exponent in range(fp32_exp_min - fp32_fraction_bits - 1, fp32_exp_max + 2):
+                denominator = 2**(fp16_fraction_bits + 1)
+                for numerator in range(0, denominator):
+                    for y in [-1.0, 0.0, 1.0]:
+                        small_delta = y / 2**fp32_fraction_bits
+                        val = (-1.0)**sign_bit * 2.0**exponent * (1.0 +
 
 Review comment:
   nit: Could we break (1.0 +  also in the next line for readability?

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