From: Christian Heller <c.heller@plomlompom.de>
Date: Sun, 26 May 2013 02:40:24 +0000 (+0200)
Subject: Use own pseudo-random number generator to ensure portable predictability.
X-Git-Tag: tce~1276
X-Git-Url: https://plomlompom.com/repos/%7B%7B%20web_path%20%7D%7D/decks/%7B%7Bprefix%7D%7D/%7B%7Byoutube_prefix%7D%7D%7B%7Bresult.id%7D%7D?a=commitdiff_plain;h=67396848cb5e3e55385a466d7a24a4f68d0a6c9c;p=plomrogue

Use own pseudo-random number generator to ensure portable predictability.
---

diff --git a/roguelike.c b/roguelike.c
index cc218a3..7b2d159 100644
--- a/roguelike.c
+++ b/roguelike.c
@@ -8,6 +8,16 @@
 #include "roguelike.h"
 #include "keybindings.h"
 
+static uint32_t seed = 0;
+
+uint16_t rrand() {
+// Pseudo-random number generator (LGC algorithm). Use instead of rand() to ensure portable predictability.
+  uint32_t a   = 1103515245;      // Values for a and b as recommended by POSIX.1-2001 (see man page rand(3)).
+  uint16_t b   =      12345;
+  uint32_t mod = 2147483648;
+  seed = ((seed * a) + b) % mod;
+  return (seed / 65536); }        // Ignore least significant 16 bits (they are less random).
+
 void toggle_window (struct WinMeta * win_meta, struct Win * win) {
 // Toggle display of window win.
   if (0 != win->curses)
@@ -43,7 +53,7 @@ struct Map init_map () {
   for (y = 0; y < map.height; y++)
     for (x = 0; x < map.width; x++) {
       terrain = '.';
-      ran = rand();
+      ran = rrand();
       if (   0 == ran % ((x*x) / 3 + 1)
           || 0 == ran % ((y*y) / 3 + 1)
           || 0 == ran % ((map.width - x - 1) * (map.width - x - 1) / 3 + 1)
@@ -66,7 +76,7 @@ void map_scroll (struct Map * map, char dir) {
 void next_turn (struct World * world) {
 // Increment turn and move enemy.
   world->turn++;
-  char d = rand() % 5;
+  char d = rrand() % 5;
   char ty = world->monster->y;
   char tx = world->monster->x;
   if (1 == d)
diff --git a/roguelike.h b/roguelike.h
index 668d52c..650ddc1 100644
--- a/roguelike.h
+++ b/roguelike.h
@@ -22,6 +22,7 @@ struct Monster {
   uint16_t y;
   uint16_t x; };
 
+uint16_t rrand();
 void toggle_window (struct WinMeta *, struct Win *);
 void growshrink_active_window (struct WinMeta *, char);
 struct Map init_map ();