implement Ivy Bridge RDRAND support

Signed-off-by: Steven Noonan <steven@uplinklabs.net>

src/rnd.c

@@ -15,6 +15,46 @@ extern int NDECL(rand);
 # endif
 #endif /* LINT */
 
+#ifdef __RDRND__
+static int
+has_rdrand(void)
+{
+	const unsigned int RDRAND_BIT = 0x40000000;
+	unsigned int eax, ebx, ecx, edx;
+
+	static int cache = -1;
+
+	if (cache != -1)
+		return cache;
+
+	eax = 1;
+	ecx = 0;
+	ebx = edx = 0;
+	asm volatile(
+		"cpuid"
+		: "=a" (eax),
+		  "=b" (ebx),
+		  "=c" (ecx),
+		  "=d" (edx)
+		: "0" (eax), "2" (ecx));
+
+	cache = (ecx & RDRAND_BIT) ? 1 : 0;
+	return cache;
+}
+
+#include <immintrin.h>
+static unsigned int rdrand()
+{
+	unsigned int x;
+	if (has_rdrand() && _rdrand32_step(&x))
+		return x;
+	else
+		return rand();
+}
+#undef RND
+#define RND(x)  (int)(rdrand() % (long)(x))
+#endif
+
 #ifdef OVL0
 
 int

sys/unix/Makefile.src

@@ -184,6 +184,11 @@ endif
 
 LFLAGS = 
 
+ifeq ($(RNG),rdrand)
+CFLAGS += -mrdrnd
+LFLAGS += -mrdrnd
+endif
+
 # The Qt and Be window systems are written in C++, while the rest of
 # NetHack is standard C.  If using Qt, uncomment the LINK line here to get
 # the C++ libraries linked in.

sys/unix/Makefile.utl

@@ -103,6 +103,11 @@ endif
 
 LFLAGS =
 
+ifeq ($(RNG),rdrand)
+CFLAGS += -mrdrnd
+LFLAGS += -mrdrnd
+endif
+
 LIBS =
 
 # If you are cross-compiling, you must use this: