Add virRandom() API to generate numbers with non-power-of-2 limit

The current virRandomBits() API is only usable if the caller wants
a random number in the range [0, n-1) where n is a power of two.
This adds a virRandom() API which generates a double in the
range [0.0,1.0) with 48 bits of entropy. It then also adds a
virRandomInt(uint32_t max) API which generates an unsigned
in the range [0,@max)

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>

src/libvirt_private.syms

@@ -1641,8 +1641,10 @@ virPidFileDeletePath;
 
 
 # virrandom.h
+virRandom;
 virRandomBits;
 virRandomGenerateWWN;
+virRandomInt;
 
 
 # virsocketaddr.h

src/util/virrandom.c

@@ -23,6 +23,7 @@
 
 #include <stdlib.h>
 #include <inttypes.h>
+#include <math.h>
 
 #include "virrandom.h"
 #include "threads.h"
@@ -108,6 +109,37 @@ uint64_t virRandomBits(int nbits)
     return ret;
 }
 
+
+/**
+ * virRandom:
+ *
+ * Generate an evenly distributed random number between [0.0,1.0)
+ *
+ * Return: a random number with 48 bits of entropy
+ */
+double virRandom(void)
+{
+    uint64_t val = virRandomBits(48);
+
+    return ldexp(val, -48);
+}
+
+
+/**
+ * virRandomInt:
+ * @max: upper limit
+ *
+ * Generate an evenly distributed random integer between [0, @max)
+ *
+ * Return: a random number between [0,@max)
+ */
+uint32_t virRandomInt(uint32_t max)
+{
+    double val = virRandom();
+    return val * max;
+}
+
+
 #define QUMRANET_OUI "001a4a"
 #define VMWARE_OUI "000569"
 #define MICROSOFT_OUI "0050f2"

src/util/virrandom.h

@@ -25,6 +25,8 @@
 # include "internal.h"
 
 uint64_t virRandomBits(int nbits);
+double virRandom(void);
+uint32_t virRandomInt(uint32_t max);
 int virRandomGenerateWWN(char **wwn, const char *virt_type);
 
 #endif /* __VIR_RANDOM_H__ */