[libvirt] [PATCH v2] Add virRandom() API to generate numbers with non-power-of-2 limit

[Daniel P. Berrange]

From: "Daniel P. Berrange" <berrange at redhat.com>

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, at max]

Signed-off-by: Daniel P. Berrange <berrange at redhat.com>
---
 src/libvirt_private.syms |  2 ++
 src/util/virrandom.c     | 32 ++++++++++++++++++++++++++++++++
 src/util/virrandom.h     |  2 ++
 3 files changed, 36 insertions(+)

diff --git a/src/libvirt_private.syms b/src/libvirt_private.syms
index 018d3a9..1905d6f 100644
--- a/src/libvirt_private.syms
+++ b/src/libvirt_private.syms
@@ -1641,8 +1641,10 @@ virPidFileDeletePath;
 
 
 # virrandom.h
+virRandom;
 virRandomBits;
 virRandomGenerateWWN;
+virRandomInt;
 
 
 # virsocketaddr.h
diff --git a/src/util/virrandom.c b/src/util/virrandom.c
index 50bed46..2092afc 100644
--- a/src/util/virrandom.c
+++ b/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);
+}
+
+
+/**
+ * virRandomInt32:
+ * @max: upper limit
+ *
+ * Generate an evenly distributed random integer between [0, at max]
+ *
+ * Return: a random number between [0, at 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"
diff --git a/src/util/virrandom.h b/src/util/virrandom.h
index 29a055d..bd34c94 100644
--- a/src/util/virrandom.h
+++ b/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__ */
-- 
1.7.11.2