rand/rand.c: Add support for x86 `RDRAND' instruction in `rand_quick'.

diff --git a/rand/rand.c b/rand/rand.c
index aa3fb45..29b180d 100644 (file)
--- a/rand/rand.c
+++ b/rand/rand.c
@@ -161,8 +161,30 @@ CPU_DISPATCH(static, return, int, quick, (rand_pool *r), (r),
 
 static int trivial_quick(rand_pool *r) { return (-1); }
 
+#if __GNUC__ && (CPUFAM_X86 || CPUFAM_AMD64)
+static int rdrand_quick(rand_pool *r)
+{
+  unsigned long rr;
+  unsigned char w;
+  int i;
+
+  for (i = 0; i < 16; i++) {
+    __asm__ ("rdrand %0; setc %1" : "=r" (rr), "=g" (w) : : "cc");
+    if (w) {
+      rand_add(r, &rr, sizeof(rr), 8*sizeof(rr));
+      return (0);
+    }
+  }
+  return (-1);
+}
+#endif
+
 static quick__functype *pick_quick(void)
 {
+#if __GNUC__ && (CPUFAM_X86 || CPUFAM_AMD64)
+  DISPATCH_PICK_COND(rand_quick, rdrand_quick,
+                    cpu_feature_p(CPUFEAT_X86_RDRAND));
+#endif
   DISPATCH_PICK_FALLBACK(rand_quick, trivial_quick);
 }