From a1933bd1847951b959016f59ee744d1b18a00142 Mon Sep 17 00:00:00 2001
From: Laurent Bercot <ska-skaware@skarnet.org>
Date: Fri, 14 Oct 2016 17:07:56 +0000
Subject:  Clean up and modernize librandom.

 Correct random number generation has historically been
suprisingly painful to achieve. There was no standard,
every system behaved in a subtly different way, and there
were a few userland initiatives to get decent randomness,
all incompatible of course.
 The situation is a bit better now, we're heading towards
some standardization. The arc4random() series of functions
is a good API, and available on a lot of systems -
unfortunately not Linux, but on Linux the new getrandom()
makes using /dev/random obsolete.

 So I removed the old crap in librandom, dropped EGD support,
dropped dynamic backend selection, made a single API series
(random_* instead of goodrandom_* and badrandom_*), added
an arc4random backend and a getrandom backend, and defaulted
to /dev/urandom backed up by SURF in the worst case. This
should be much smaller and logical. However, it's a major
API break, so the skarnet.org stack will be changed to
adapt.
---
 src/librandom/random_uint32.c | 56 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 56 insertions(+)
 create mode 100644 src/librandom/random_uint32.c

(limited to 'src/librandom/random_uint32.c')

diff --git a/src/librandom/random_uint32.c b/src/librandom/random_uint32.c
new file mode 100644
index 0000000..d011885
--- /dev/null
+++ b/src/librandom/random_uint32.c
@@ -0,0 +1,56 @@
+/* ISC license. */
+
+#include <skalibs/sysdeps.h>
+
+#ifdef SKALIBS_HASARC4RANDOM
+
+#include <stdlib.h>
+#include <skalibs/random.h>
+
+uint32 random_uint32 (uint32 n)
+{
+  return arc4random_uniform(n) ;
+}
+
+#else
+
+#include <skalibs/uint32.h>
+#include <skalibs/random.h>
+
+static inline uint32 random_mask2 (register uint32 n)
+{
+  for (;;)
+  {
+    register uint32 m = n | (n >> 1) ;
+    if (m == n) return n ;
+    n = m ;
+  }
+}
+
+static inline unsigned int random_nchars (register uint32 n)
+{
+  return n <= 0xff ? 1 :
+         n <= 0xffff ? 2 :
+         n <= 0xffffffUL ? 3 : 4 ;
+}
+
+uint32 random_uint32 (uint32 n)
+{
+  if (!n) return 0 ;
+  else
+  {
+    uint32 i = n, m = random_mask2(n-1) ;
+    unsigned int nchars = random_nchars(n) ;
+    char tmp[4] ;
+    while (i >= n)
+    {
+      random_string(tmp, nchars) ;
+      byte_zero(tmp + nchars, 4 - nchars) ;
+      uint32_unpack(tmp, &i) ;
+      i &= m ;
+    }
+    return i ;
+  }
+}
+
+#endif
-- 
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