Refactor/RNG system (#476)

* Extract rng manipulation to its own file

* clang format

* Get CPU cycles since game start to use for RNG

* change a few things

* clang format

* Implement suggestions from @ricfehr3

* clang format

* Fix rebase issue

* clang format

* Create RngInfo struct to hold seed and step

* clang format

* Make a note about rng_restore system not having been tested properly yet

* Apply suggestions from @ricfehr3

Co-authored-by: Rickey <ric@rf3.xyz>

* clang format

---------

Co-authored-by: MathisMartin31 <mathis.martin31@gmail.com>
Co-authored-by: Rickey <ric@rf3.xyz>

include/game.h

@@ -175,8 +175,6 @@ void display_mult(void);
 void display_money(void);
 void set_retrigger(bool new_retrigger);
 
-u32 get_rand(void);
-
 // joker specific functions
 bool is_shortcut_joker_active(void);
 int get_straight_and_flush_size(void);

include/game_variables.h

@@ -7,6 +7,7 @@
 #define GAME_VARIABLES_H
 
 #include "blind.h"
+#include "random.h"
 
 #include <tonc.h>
 
@@ -37,8 +38,7 @@ typedef struct
     // Internal variables
 
     s32 timer; // This might already exist in libtonc but idk so i'm just making my own
-    u32 rng_seed;
-    u32 rng_step; // Position in the rng sequence.
+    RngInfo rng_info;
 
     // Variables visible by the player
 

include/random.h

@@ -0,0 +1,76 @@
+/**
+ * @file random.h
+ *
+ * @brief Common functions to handle RNG manipulation. Using this interface has three goals:
+ * 1. Make RNG repeatable so that people can share seeds and saves, and end up with the same run
+ * 2. Prevent the players from engaging in save-scumming since the pseudo-RNG is deterministic
+ * 3. Accomodate for base-36 seeds, so that we can freely chose one with alpha-numeric characters in
+ * the seed screen input
+ */
+#ifndef RANDOM_H
+#define RANDOM_H
+
+#include <tonc.h>
+
+/**
+ * @brief Hex value of "ZZZZZZ" in base 36
+ */
+#define MAX_SEED 0x81BF0FFF
+
+/**
+ * @brief Information to track and restore RNG state
+ */
+typedef struct
+{
+    /** Initial seed */
+    u32 seed;
+    /** Position in the rng sequence. */
+    u32 step;
+} RngInfo;
+
+/**
+ * @brief Starts counting CPU cycles, this will be used by rng_shuffle_seed to
+ *         generate a more random seed. To be called once on game start.
+ */
+void rng_init(void);
+
+/**
+ * @brief Update the CPU cycles counter and accumulate it into a bigger u32 `timer_acc` variable.
+ */
+void rng_update(void);
+
+/**
+ * @brief Set the rng seed to the chosen value, and reset the step counter to 0.
+ *         The seed will be capped at `MAX_SEED` for compatibility with the Seed Input screen
+ *         used to choose a seed for seeded runs.
+ *
+ * @param seed the new RNG seed
+ */
+void rng_set_seed(u32 seed);
+
+/**
+ * @brief Uses the CPU cycles counter to randomize the RNG seed as much as possible.
+ *         This will be called by the main menu and the game over screens so that
+ *         the next run's seed isn't the same as the last's.
+ *         rng_start_sampling needs to have been called, and will stop the profiling.
+ */
+void rng_shuffle_seed(void);
+
+/**
+ * @brief Get the next "randomly" generated number in the sequence from the current seed.
+ *
+ * @return u32
+ */
+u32 rng_get_u32(void);
+
+/**
+ * @brief Restore RNG info struct in the GameVariables. Sets the `seed` and seeks the
+ *         position `step` in the rng sequence.
+ *
+ * @param info RngInfo struct applied
+ *
+ * @note Consistency of the RNG after reloading the RngInfo struct has yet to be tested properly
+ */
+void rng_restore(RngInfo info);
+
+#endif // RANDOM_H