cleanup

[rpikern] / src / libc / rand.c

diff --git a/src/libc/rand.c b/src/libc/rand.c
new file mode 100644 (file)
index 0000000..6ea2624
--- /dev/null
+++ b/src/libc/rand.c
@@ -0,0 +1,48 @@
+/* random number generator, based on this description of the algorithm
+ * used by the GNU libc: https://www.mathstat.dal.ca/~selinger/random
+ */
+#include <stdlib.h>
+#include <inttypes.h>
+
+static int init_done;
+static int32_t rng[34];
+static int32_t *ptr0, *ptr1;
+
+int rand(void)
+{
+       int res;
+
+       if(!init_done) {
+               srand(1);
+       }
+
+       *ptr1 += *ptr0;
+       res = (uint32_t)*ptr1 >> 1;
+       if(++ptr0 >= rng + 34) ptr0 = rng;
+       if(++ptr1 >= rng + 34) ptr1 = rng;
+
+       return res;
+}
+
+void srand(unsigned int seed)
+{
+       int i;
+
+       init_done = 1;
+       if(seed == 0) seed = 1;
+
+       rng[0] = seed;
+       for(i=1; i<31; i++) {
+               rng[i] = (16807 * rng[i - 1]) % RAND_MAX;
+               if(rng[i] < 0) rng[i] += RAND_MAX;
+       }
+       for(i=31; i<34; i++) {
+               rng[i] = rng[i - 31];
+       }
+       ptr0 = rng + 3;
+       ptr1 = rng + 31;
+
+       for(i=34; i<344; i++) {
+               rand();
+       }
+}