From a92649f9185dad6565a4c09a4def41d7843f8896 Mon Sep 17 00:00:00 2001
From: Norbert Manthey <nmanthey@amazon.de>
Date: Tue, 29 Sep 2020 14:38:46 +0200
Subject: [PATCH] rand: add prng

This commit adds the ability to use random numbers with a seed, via the
known methods rand() and srand().

As generator, a simple linear congruential generator is used, with the
same parameters as used in musl or newlib.

Signed-off-by: Norbert Manthey <nmanthey@amazon.de>
---
 include/lib.h | 4 ++++
 lib/lib.c     | 9 +++++++++
 2 files changed, 13 insertions(+)

diff --git a/include/lib.h b/include/lib.h
index 75503feb..b243a809 100644
--- a/include/lib.h
+++ b/include/lib.h
@@ -385,4 +385,8 @@ static inline unsigned int next_power_of_two(unsigned int n) {
 
 extern void halt(void);
 
+extern void srand(unsigned s);
+
+extern int rand(void);
+
 #endif /* KTF_LIB_H */
diff --git a/lib/lib.c b/lib/lib.c
index 07f220c2..053e638d 100644
--- a/lib/lib.c
+++ b/lib/lib.c
@@ -33,3 +33,12 @@ void __noreturn halt(void) {
         pause();
     }
 }
+
+static uint64_t seed;
+
+void srand(unsigned s) { seed = s - 1; }
+
+int rand(void) {
+    seed = 6364136223846793005ULL * seed + 1;
+    return seed >> 33;
+}