random: Use a different RNG for testing

This RNG is more predictable, which makes it great for testing.

Signed-off-by: Anna Schumaker <Anna@OcarinaProject.net>

DESIGN

@@ -828,6 +828,26 @@ Track Tag:
 
 
 
+Random:
+	The random number generator is used by the Queue to pick a song as
+	randomly as possible.  I use two different RNG implementations,
+	depending on if Ocarina is compiled with CONFIG_TEST or not.
+
+	When CONFIG_TEST is enabled, the RNG is a simple counter.  Every time
+	_pick_random() is called, the counter is incremented and returned.
+	When compiled without CONFIG_TEST we will return values using the
+	rand() function from stdlib.h.
+
+- API:
+	void random_seed(unsigned int n);
+		Seed the random number generator based on n.
+
+	void random(unsigned int min, unsigned int max);
+		Return a random number between min and max, inclusive.
+		If min >= max: return min.
+
+
+
 Queue:
 	Queues are lists of songs that the user has requested to play.  They
 	are the main interface for all music played by Ocarina.

include/random.h

@@ -0,0 +1,36 @@
+/*
+ * Copyright 2014 (c) Anna Schumaker
+ */
+
+#ifndef OCARINA_RANDOM_H
+#define OCARINA_RANDOM_H
+
+#ifndef CONFIG_TEST
+
+#include <stdlib.h>
+static inline void _seed_random(unsigned int n) { srand(time(NULL) + n); }
+static inline unsigned int _pick_random() { return rand(); }
+
+#else /* CONFIG_TEST */
+
+void _seed_random(unsigned int);
+unsigned int _pick_random();
+
+#endif /* CONFIG_TEST */
+
+
+
+static inline void random_seed(unsigned int n)
+{
+	_seed_random(n);
+}
+
+static inline unsigned int random(unsigned int min, unsigned int max)
+{
+	if (min >= max)
+		return min;
+	return min + (_pick_random() % (max - min));
+}
+
+
+#endif /* OCARINA_RANDOM_H */

lib/random.cpp

@@ -0,0 +1,21 @@
+/*
+ * Copyright 2014 (c) Anna Schumaker
+ */
+#ifdef CONFIG_TEST
+
+#include <random.h>
+
+static unsigned int _random_value = 0;
+
+
+void _seed_random(unsigned int n)
+{
+	_random_value = n;
+}
+
+unsigned int _pick_random()
+{
+	return ++_random_value;
+}
+
+#endif /* CONFIG_TEST */

tests/.gitignore

@@ -5,4 +5,5 @@ index
 filter
 idle
 tags
+random
 queue

tests/Sconscript

@@ -16,6 +16,7 @@ tests = [
 	("filter.cpp",   True,  [], []),
 	("idle.cpp",     False, [ "idle.cpp" ], []),
 	("tags.cpp",     True,  [], [ "taglib" ]),
+	("random.cpp",   False, [ "random.cpp" ], []),
 	("queue.cpp",    True,  [ "callback.cpp" ], []),
 
 ]

tests/random.cpp

@@ -0,0 +1,36 @@
+/*
+ * Copyright 2014 (c) Anna Schumaker.
+ */
+
+#include <random.h>
+#include "test.h"
+
+#include <sstream>
+
+static void do_test_rng(unsigned int seed)
+{
+	random_seed(seed);
+
+	for (unsigned int i = 0; i <= 10; i++) {
+		if (i <= seed)
+			test_equal(random(seed, i), seed);
+		else
+			test_equal(random(seed, i), seed + (i % (i - seed)));
+	}
+}
+
+static void test_rng(unsigned int seed)
+{
+	std::stringstream ss;
+	ss << " (seed = " << seed << ")";
+	std::string seed_str = ss.str();
+
+	run_test("Random Number Generator Test" + seed_str, do_test_rng, seed);
+}
+
+int main(int argc, char **argv)
+{
+	for (unsigned int i = 0; i < 10; i++)
+		test_rng(i);
+	return 0;
+}