1 files changed, 87 insertions, 0 deletions
diff --git a/xs_random.h b/xs_random.h
new file mode 100644
index 0000000..3566827
--- /dev/null
+++ b/xs_random.h
@@ -0,0 +1,87 @@
+/* copyright (c) 2022 - 2023 grunfink / MIT license */
+
+#ifndef _XS_RANDOM_H
+
+#define _XS_RANDOM_H
+
+unsigned int xs_rnd_int32_d(unsigned int *seed);
+void *xs_rnd_buf(void *buf, int size);
+
+#ifdef XS_IMPLEMENTATION
+
+#include <stdio.h>
+#include <sys/time.h>
+#include <unistd.h>
+#include <stdlib.h>
+
+unsigned int xs_rnd_int32_d(unsigned int *seed)
+/* returns a deterministic random integer. If seed is NULL, uses a static one */
+{
+    static unsigned int s = 0;
+
+    if (seed == NULL)
+        seed = &s;
+
+    if (*seed == 0) {
+        struct timeval tv;
+
+        gettimeofday(&tv, NULL);
+        *seed = tv.tv_sec ^ tv.tv_usec ^ getpid();
+    }
+
+    /* Linear congruential generator by Numerical Recipes */
+    *seed = (*seed * 1664525) + 1013904223;
+
+    return *seed;
+}
+
+
+void *xs_rnd_buf(void *buf, int size)
+/* fills buf with random data */
+{
+#ifdef __OpenBSD__
+
+    /* available since OpenBSD 2.2 */
+    arc4random_buf(buf, size);
+
+#else
+
+    FILE *f;
+    int done = 0;
+
+    if ((f = fopen("/dev/urandom", "r")) != NULL) {
+        /* fill with great random data from the system */
+        if (fread(buf, size, 1, f) == 1)
+            done = 1;
+
+        fclose(f);
+    }
+
+    if (!done) {
+        /* fill the buffer with poor quality, deterministic data */
+        unsigned int s   = 0;
+        unsigned char *p = (unsigned char *)buf;
+        int n            = size / sizeof(s);
+
+        /* fill with full integers */
+        while (n--) {
+            xs_rnd_int32_d(&s);
+            p = memcpy(p, &s, sizeof(s)) + sizeof(s);
+        }
+
+        if ((n = size % sizeof(s))) {
+            /* fill the remaining */
+            xs_rnd_int32_d(&s);
+            memcpy(p, &s, n);
+        }
+    }
+
+#endif /* __OpenBSD__ */
+
+    return buf;
+}
+
+
+#endif /* XS_IMPLEMENTATION */
+
+#endif /* XS_RANDOM_H */