Juan 13/09/2022: add new ARCH_SRC/cray_gu/gu.c , for Automatic Gradual Underflow on CPU (like GPU)

src/ARCH_SRC/cray_gu/gu.c

+/*
+
+*  Copyright -2022 Hewlett Packard Enterprise Development LP
+
+*/
+
+void __cce_floatingpt_gu( void ); // Gradual Underflow.
+
+ 
+
+static void (*p)(void)  __attribute__((section(".init_array"))) = __cce_floatingpt_gu;
+
+ 
+
+#define DENORMS_ARE_ZEROS                      6
+
+#define FLUSH_TO_ZERO_MASK                    15
+
+ 
+
+void __cce_floatingpt_gu( void )
+
+{
+
+  unsigned long gu_src = (1 << DENORMS_ARE_ZEROS);
+
+  unsigned long gu_dst = (1 << FLUSH_TO_ZERO_MASK);
+
+ 
+
+  do {
+
+      unsigned long __mxcsr;
+
+      __asm__ volatile("stmxcsr %0" : : "m" (__mxcsr));
+
+      __mxcsr &= ~(gu_src | gu_dst);
+
+      __asm__ volatile("ldmxcsr %0" : : "m" (__mxcsr));
+
+  }
+
+  while (0);
+
+}