libc: stdlib: POSIX-compliant randomness

This commit implements two functions: rand(), and srand()
which together allow for the generation of pseudorandom
numbers.

Signed-off-by: AptRock327 <dominik032009@gmail.com>
Signed-off-by: Ian Moffett <ian@osmora.org>

1 files changed, 63 insertions, 0 deletions

diff --git a/lib/libc/src/stdlib/rand.c b/lib/libc/src/stdlib/rand.c
new file mode 100644
index 0000000..8a0899f
--- /dev/null
+++ b/lib/libc/src/stdlib/rand.c
@@ -0,0 +1,63 @@
+/*
+ * Copyright (c) 2023-2024 Ian Marco Moffett and the Osmora Team.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice,
+ *    this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of Hyra nor the names of its
+ *    contributors may be used to endorse or promote products derived from
+ *    this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <stdlib.h>
+
+/* linear feedback shift register - static global variable */
+static unsigned int lfsr = 0;
+
+/*
+ * Sets the global LFSR to a provided seed
+ *
+ * @seed: Seed that will be used for random number generation
+ */
+void
+srand(unsigned int seed)
+{
+    lfsr = seed;
+}
+
+/*
+ * Generates a random number between 0 and RAND_MAX
+ *
+ * Returns random number (unsigned int) between 0 and RAND_MAX
+ */
+unsigned int
+rand(void)
+{
+    unsigned int intResult = 0;
+    unsigned int bitResult;
+    for(int i = 0; i < 32; i++) {
+        bitResult = lfsr % 2;
+        intResult |= (bitResult << i);
+        lfsr >>= 1;
+        lfsr |= ((bitResult ^ (lfsr % 2)) << 31);
+    }
+    return intResult;
+}