1 files changed, 52 insertions, 0 deletions
diff --git a/libgloss/m68k/atari/atari-getentropy.c b/libgloss/m68k/atari/atari-getentropy.c
new file mode 100644
index 0000000..0b5b461
--- /dev/null
+++ b/libgloss/m68k/atari/atari-getentropy.c
@@ -0,0 +1,52 @@
+/*
+	Copyright (C) 2025 Mikael Hildenborg
+	SPDX-License-Identifier: BSD-2-Clause
+*/
+
+#include <_ansi.h>
+#include <_syslist.h>
+#include <errno.h>
+#include "atari-gem_errno.h"
+#include "atari-traps.h"
+
+/*
+    Xorshift pseudorandom number generator.
+    https://en.wikipedia.org/wiki/Xorshift
+    Inited with random seed.
+*/
+
+int getentropy(void *buf, size_t buflen)
+{
+    unsigned int a;
+    unsigned int state[4];
+
+    // Init state
+    a = trap14_11();     // Atari Random func.
+    for (int i = 0; i < 4; ++i)
+    {
+        // xorshift32
+        a ^= (a << 13);
+        a ^= (a >> 17);
+        a ^= (a << 5);
+        state[i] = a;
+    }
+
+    for (size_t i = 0; i < buflen; ++i)
+    {
+        // xorshift128
+        unsigned int t = state[3];
+        unsigned int s = state[0];
+        state[3] = state[2];
+        state[2] = state[1];
+        state[1] = s;
+
+        t ^= t << 11;
+        t ^= t >> 7;
+        state[0] = t ^ s ^ (s >> 19);
+
+        // use lowest byte (could be optimized to adapt to buf len and output whole 32 bits when possible.)
+        ((unsigned char*)buf)[i] = (unsigned char)state[0];
+    }
+
+    return 0;
+}