Add support for fp16/fp16alt to double and double to fp16/fp16alt. Fl…

…oatlib.c + t-elf to have it compile. This is a bit of a hack and could be done in a more generic manner

libgcc/config/riscv/floatlib.c

@@ -0,0 +1,46 @@
+#ifdef __gap9__
+
+/* Convert half to double */
+double __extendhfdf2 (float16 a1)
+
+{
+        register float F;
+        __asm ("fcvt.s.h %0, %1" : "=r" (F) : "r" (a1) );
+        return F;
+}
+
+/* */
+
+/* Convert alternative half to double */
+double __extendohfdf2 (float16alt a1)
+
+{
+	float F;
+	__asm ("fcvt.s.ah %0, %1" : "=r" (F) : "r" (a1) );
+	return F;
+}
+
+
+/* Truncate double to half*/
+float16 __truncdfhf2 (double a1)
+
+{
+	register float F = a1;
+	float16 R;
+	__asm ("fcvt.h.s %0, %1" : "=r" (R) : "r" (F) );
+	return R;
+
+}
+
+/* Truncate double to alternative half*/
+float16alt __truncdfohf2 (double a1)
+
+{
+	register float F = a1;
+	float16alt R;
+	__asm ("fcvt.ah.s %0, %1" : "=r" (R) : "r" (F) );
+	return R;
+
+}
+
+#endif

libgcc/config/riscv/t-elf

@@ -3,4 +3,5 @@ LIB2ADD += $(srcdir)/config/riscv/save-restore.S \
 	   $(srcdir)/config/riscv/multi3.S \
 	   $(srcdir)/config/riscv/div.S \
 	   $(srcdir)/config/riscv/atomic.c \
+	   $(srcdir)/config/riscv/floatlib.c \