Rewrite csrand_interval() as a wrapper around csrand_uniform()

The old code didn't produce very good random numbers.  It had a bias.
And that was from performing some unnecessary floating-point
calculations that overcomplicate the problem.

Cc: "Jason A. Donenfeld" <Jason@zx2c4.com>
Cc: Cristian Rodríguez <crrodriguez@opensuse.org>
Cc: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Cc: Björn Esser <besser82@fedoraproject.org>
Cc: Yann Droneaud <ydroneaud@opteya.com>
Cc: Joseph Myers <joseph@codesourcery.com>
Cc: Sam James <sam@gentoo.org>
Signed-off-by: Alejandro Colomar <alx@kernel.org>

libmisc/csrand.c

@@ -85,3 +85,13 @@ csrand_uniform(unsigned long n)
 
 	return r;
 }
+
+
+/*
+ * Return a uniformly-distributed CS random value in the interval [min, max].
+ */
+unsigned long
+csrand_interval(unsigned long min, unsigned long max)
+{
+	return csrand_uniform(max - min + 1) + min;
+}