X-Git-Url: http://git.mutantstargoat.com/user/nuclear/?p=rpikern;a=blobdiff_plain;f=src%2Flibc%2Frand.c;fp=src%2Flibc%2Frand.c;h=6ea26248cbdc86ce22ccfe6f4357d584a01314a7;hp=0000000000000000000000000000000000000000;hb=32ccc707bc0821d7ff4248fe9f58e92e9c6ebef9;hpb=203b43a75a028e9238307bd6e73768eb8e942071

diff --git a/src/libc/rand.c b/src/libc/rand.c
new file mode 100644
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();
+	}
+}