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 <[email protected]>
KernelTestFramework · Sep 29, 2020 · a92649f · a92649f
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commit a92649f
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diff --git 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
@@ -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;
+}