hot fix log (#14293)

chengduo · web-flow · commit ffc866159fcd · 2018-11-07T14:50:10.000+08:00
test=develop
diff --git a/paddle/fluid/operators/math/cross_entropy.cu b/paddle/fluid/operators/math/cross_entropy.cu
@@ -28,7 +28,7 @@ __device__ __forceinline__ double real_log(double x) { return log(x); }
 
 __device__ __forceinline__ platform::float16 real_log(
     const platform::float16& val) {
-  return static_cast<platform::float16>(hlog(static_cast<half>(val)));
+  return static_cast<platform::float16>(logf(static_cast<float>(val)));
 }
 
 template <typename T>

Original file line number	Diff line number	Diff line change
`@@ -28,7 +28,7 @@ __device__ __forceinline__ double real_log(double x) { return log(x); }`
`28`	`28`
`29`	`29`	`__device__ __forceinline__ platform::float16 real_log(`
`30`	`30`	`const platform::float16& val) {`
`31`		`- return static_cast<platform::float16>(hlog(static_cast<half>(val)));`
	`31`	`+ return static_cast<platform::float16>(logf(static_cast<float>(val)));`
`32`	`32`	`}`
`33`	`33`
`34`	`34`	`template <typename T>`