prng: fix rand() to give good sequence with small state

[musl] / src / prng / rand.c

diff --git a/src/prng/rand.c b/src/prng/rand.c
index e3ce634..c000cd2 100644 (file)
--- a/src/prng/rand.c
+++ b/src/prng/rand.c
@@ -1,6 +1,7 @@
 #include <stdlib.h>
+#include <stdint.h>
 
-static unsigned seed;
+static uint64_t seed;
 
 void srand(unsigned s)
 {
@@ -9,5 +10,6 @@ void srand(unsigned s)
 
 int rand(void)
 {
-       return (seed = (seed+1) * 1103515245 + 12345 - 1)+1 & 0x7fffffff;
+       seed = 6364136223846793005ULL*seed + 1;
+       return seed>>33;
 }