[SYCL][libdevice] Add type cast functions between half and float/integral type (#6930)

Signed-off-by: jinge90 <[email protected]>

Author: jinge90

libdevice/device.h

@@ -40,4 +40,13 @@
 #define DEVICE_EXTERN_C_INLINE DEVICE_EXTERN_C __attribute__((always_inline))
 #endif // __LIBDEVICE_HOST_IMPL__
 
+// Rounding mode are used internally by type convert functions in imf libdevice
+//  and we don't want to include system's fenv.h, so we define ourselves'.
+typedef enum {
+  __IML_RTE, // round to nearest-even
+  __IML_RTZ, // round to zero
+  __IML_RTP, // round to +inf
+  __IML_RTN, // round to -inf
+} __iml_rounding_mode;
+
 #endif // __LIBDEVICE_DEVICE_H__

libdevice/device_imf.hpp

@@ -90,6 +90,7 @@ static inline TyFP __integral2FP_host(TyINT x, int rdMode) {
   fesetround(roundingOriginal);
   return res;
 }
+#pragma STDC FENV_ACCESS OFF
 #endif // __LIBDEVICE_HOST_IMPL__
 
 template <typename Ty> static inline Ty __imax(Ty x, Ty y) {