From 4c96aac02cd78f7fd2d054906d5c4ca2e2c6c5bf Mon Sep 17 00:00:00 2001
From: Imbus <>
Date: Tue, 2 Sep 2025 01:59:24 +0200
Subject: [PATCH] Badrand pseudo random number generator, emphasis on pseudo

---
 Makefile               |  3 ++-
 kern/libkern/badrand.c | 35 ++++++++++++++++++++++++++++++++++
 kern/libkern/badrand.h | 43 ++++++++++++++++++++++++++++++++++++++++++
 kern/libkern/stdint.h  | 15 +++++++++++++++
 4 files changed, 95 insertions(+), 1 deletion(-)
 create mode 100644 kern/libkern/badrand.c
 create mode 100644 kern/libkern/badrand.h

diff --git a/Makefile b/Makefile
index c9e8c3c..928c492 100644
--- a/Makefile
+++ b/Makefile
@@ -59,7 +59,8 @@ KERNEL_OBJ := \
 	kern/libkern/memory.o \
 	kern/libkern/spinlock.o \
 	kern/libkern/mini-printf.o \
-	kern/libkern/stdio.o
+	kern/libkern/stdio.o \
+	kern/libkern/badrand.o
 
 kern/kernel.elf: $(KERNEL_OBJ)
 	@echo LD $@
diff --git a/kern/libkern/badrand.c b/kern/libkern/badrand.c
new file mode 100644
index 0000000..48df698
--- /dev/null
+++ b/kern/libkern/badrand.c
@@ -0,0 +1,35 @@
+#include "badrand.h"
+#include <stdint.h>
+
+#define PRAND_BUILD_SEED                                                                                               \
+    ((uint64_t)(__TIME__[0]) * (uint64_t)(__TIME__[1]) * (uint64_t)(__TIME__[3]) * (uint64_t)(__TIME__[4]) *           \
+     (uint64_t)(__TIME__[6]) * (uint64_t)(__TIME__[7]))
+
+static uint64_t seed = PRAND_BUILD_SEED * 6364136223846793005ULL + 1;
+
+uint64_t badrand() {
+    seed = seed * 6364136223846793005ULL + 1;
+    return seed;
+}
+
+uint64_t badrand_range(uint64_t min, uint64_t max) {
+    uint64_t range = max - min + 1;
+    uint64_t x;
+    uint64_t limit = UINT64_MAX - (UINT64_MAX % range);
+
+    do {
+        x = badrand();
+    } while (x > limit);
+
+    return min + (x % range);
+}
+
+void sbadprand(uint64_t s) {
+    if (s) {
+        seed ^= (s * 0x9e3779b97f4a7c15ULL) + (seed << 6) + (seed >> 2);
+    } else {
+        seed ^= PRAND_BUILD_SEED;
+    }
+}
+
+#undef PRAND_BUILD_SEED
diff --git a/kern/libkern/badrand.h b/kern/libkern/badrand.h
new file mode 100644
index 0000000..8a0ab9c
--- /dev/null
+++ b/kern/libkern/badrand.h
@@ -0,0 +1,43 @@
+#ifndef BADRAND_H
+#define BADRAND_H
+
+#include <stdint.h>
+
+/*
+ * This is a PRNG for non-cryptographic use.
+ *
+ * See:
+ *      https://en.wikipedia.org/wiki/Linear_congruential_generator
+ */
+
+/**
+ * @brief Sets the seed for the PRNG.
+ *
+ * @param s The specific seed value or zero. If zero is passed, it will call
+ * rand_reseed().
+ */
+void sbadrand(uint64_t s);
+
+/**
+ * @brief Generates a pseudo-random 64-bit number.
+ *
+ * Uses a simple Linear Congruential Generator (LCG) to produce
+ * a sequence of pseudo-random numbers.
+ *
+ * @return A pseudo-random 64-bit unsigned integer.
+ */
+uint64_t badrand();
+
+/**
+ * @brief Generates a random number within a specified range.
+ *
+ * Produces a random number in the inclusive range [min, max].
+ * Ensures uniform distribution by applying a modulo operation.
+ *
+ * @param min The lower bound of the range (inclusive).
+ * @param max The upper bound of the range (inclusive).
+ * @return A random number between min and max.
+ */
+uint64_t badrand_range(uint64_t min, uint64_t max);
+
+#endif // BADRAND_H
diff --git a/kern/libkern/stdint.h b/kern/libkern/stdint.h
index 0ce4c00..095e598 100644
--- a/kern/libkern/stdint.h
+++ b/kern/libkern/stdint.h
@@ -12,3 +12,18 @@ typedef unsigned long  uint64_t;
 typedef uint64_t       size_t;
 
 typedef uint64_t uintptr_t;
+
+#define INT8_MIN  (-128)
+#define INT16_MIN (-32767 - 1)
+#define INT32_MIN (-2147483647 - 1)
+#define INT64_MIN (-__INT64_C(9223372036854775807) - 1)
+
+#define INT8_MAX  (127)
+#define INT16_MAX (32767)
+#define INT32_MAX (2147483647)
+#define INT64_MAX (__INT64_C(9223372036854775807))
+
+#define UINT8_MAX  (255)
+#define UINT16_MAX (65535)
+#define UINT32_MAX (4294967295U)
+#define UINT64_MAX (__UINT64_C(18446744073709551615))