- (djm) [openbsd-compat/bsd-arc4random.c openbsd-compat/openbsd-compat.c]

     [configure.ac] Implement arc4random_buf(), import implementation of
     arc4random_uniform() from OpenBSD

1 files changed, 65 insertions, 0 deletions

diff --git a/openbsd-compat/bsd-arc4random.c b/openbsd-compat/bsd-arc4random.c
index d45fb182a..8bf31e5d3 100644
--- a/openbsd-compat/bsd-arc4random.c
+++ b/openbsd-compat/bsd-arc4random.c
@@ -82,3 +82,68 @@ arc4random_stir(void)
         rc4_ready = REKEY_BYTES;
 }
 #endif /* !HAVE_ARC4RANDOM */
+
+#ifndef ARC4RANDOM_BUF
+void
+arc4random_buf(void *_buf, size_t n)
+{
+        size_t i;
+        u_int32_t r;
+        char *buf = (char *)_buf;
+
+        for (i = 0; i < n; i++) {
+                if (i % 4 == 0)
+                        r = arc4random();
+                buf[i] = r & 0xff;
+                r >>= 8;
+        }
+        i = r = 0;
+}
+#endif /* !HAVE_ARC4RANDOM_BUF */
+
+#ifndef ARC4RANDOM_UNIFORM
+/*
+ * Calculate a uniformly distributed random number less than upper_bound
+ * avoiding "modulo bias".
+ *
+ * Uniformity is achieved by generating new random numbers until the one
+ * returned is outside the range [0, 2**32 % upper_bound).  This
+ * guarantees the selected random number will be inside
+ * [2**32 % upper_bound, 2**32) which maps back to [0, upper_bound)
+ * after reduction modulo upper_bound.
+ */
+u_int32_t
+arc4random_uniform(u_int32_t upper_bound)
+{
+        u_int32_t r, min;
+
+        if (upper_bound < 2)
+                return 0;
+
+#if (ULONG_MAX > 0xffffffffUL)
+        min = 0x100000000UL % upper_bound;
+#else
+        /* Calculate (2**32 % upper_bound) avoiding 64-bit math */
+        if (upper_bound > 0x80000000)
+                min = 1 + ~upper_bound;         /* 2**32 - upper_bound */
+        else {
+                /* (2**32 - (x * 2)) % x == 2**32 % x when x <= 2**31 */
+                min = ((0xffffffff - (upper_bound << 2)) + 1) % upper_bound;
+        }
+#endif
+
+        /*
+         * This could theoretically loop forever but each retry has
+         * p > 0.5 (worst case, usually far better) of selecting a
+         * number inside the range we need, so it should rarely need
+         * to re-roll.
+         */
+        for (;;) {
+                r = arc4random();
+                if (r >= min)
+                        break;
+        }
+
+        return r % upper_bound;
+}
+#endif /* !HAVE_ARC4RANDOM_UNIFORM */