[#48] Add Rand API and make StrRandom() use it.

src/Rand.c

@@ -0,0 +1,83 @@
+/*
+ * Copyright (C) 2022-2023 Jordan Bancino <@jordan:bancino.net>
+ *
+ * Permission is hereby granted, free of charge, to any person
+ * obtaining a copy of this software and associated documentation files
+ * (the "Software"), to deal in the Software without restriction,
+ * including without limitation the rights to use, copy, modify, merge,
+ * publish, distribute, sublicense, and/or sell copies of the Software,
+ * and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT.  IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
+ * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
+ * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+ * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+#include <Rand.h>
+
+#include <Util.h>
+
+#include <stdlib.h>
+#include <pthread.h>
+#include <unistd.h>
+
+/* Generate random numbers using rejection sampling.
+* The basic idea is to "reroll" if a number happens to be
+* outside the range. However this could be extremely inefficient.
+*
+* Another idea would just be to "reroll" if the generated number
+* ends up in the previously "biased" range, and THEN do a modulo.
+*
+* This would be far more efficient for small values of max,
+* and fixes the bias issue. */
+
+/* This algorithm therefore computes N random numbers generally in 
+ * O(N) time, while being less biased. */
+void
+RandIntN(int * buf, size_t size, unsigned int max)
+{
+    static pthread_mutex_t seedLock = PTHREAD_MUTEX_INITIALIZER;
+    static unsigned int seed = 0;
+    int tmp;
+    /* Limit the range to banish all previously biased results */
+    const int allowed = RAND_MAX - RAND_MAX % max;
+
+    size_t i;
+
+    pthread_mutex_lock(&seedLock);
+    if (!seed)
+    {
+        /* Generate a seed from the system time, PID, and TID */
+        seed = UtilServerTs() ^ getpid() ^ (unsigned long) pthread_self();
+    }
+    
+    /* Generate {size} random numbers. */
+    for (i = 0; i < size; i++)
+    {
+        /* Most of the time, this will take about 1 loop */
+        do
+        {
+            tmp = rand_r(&seed);
+        } while (tmp >= allowed);
+        /* Since a generated number here is never in the biased range,
+         * we can now safely use modulo. */
+        buf[i] = tmp % max;
+    }
+    pthread_mutex_unlock(&seedLock);
+}
+/* Generate just 1 random number */
+int
+RandInt(unsigned int max)
+{
+    int val = 0;
+    RandIntN(&val, 1, max);
+    return val;
+}

src/Str.c

@@ -25,6 +25,7 @@
 
 #include <Memory.h>
 #include <Util.h>
+#include <Rand.h>
 
 #include <stdlib.h>
 #include <string.h>
@@ -153,10 +154,9 @@ char *
 StrRandom(size_t len)
 {
     static const char charset[] = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
-    static pthread_mutex_t seedLock = PTHREAD_MUTEX_INITIALIZER;
-    static unsigned int seed = 0;
 
     char *str;
+    int * nums;
     size_t i;
 
     if (!len)
@@ -165,25 +165,27 @@ StrRandom(size_t len)
     }
 
     str = Malloc(len + 1);
+
     if (!str)
     {
         return NULL;
     }
 
-    pthread_mutex_lock(&seedLock);
-
-    if (!seed)
+    nums = Malloc(len);
+    if (!nums)
     {
-        seed = UtilServerTs() ^ getpid() ^ (unsigned long) pthread_self();
+        Free(str);
+        return NULL;
     }
 
+    /* TODO: This seems slow. */
+    RandIntN(nums, len, sizeof(charset) - 1);
     for (i = 0; i < len; i++)
     {
-        str[i] = charset[rand_r(&seed) % (sizeof(charset) - 1)];
+        str[i] = charset[nums[i]];
     }
 
-    pthread_mutex_unlock(&seedLock);
-
+    Free(nums);
     str[len] = '\0';
     return str;
 }

src/include/Rand.h

@@ -0,0 +1,35 @@
+/*
+ * Copyright (C) 2022-2023 Jordan Bancino <@jordan:bancino.net>
+ *
+ * Permission is hereby granted, free of charge, to any person
+ * obtaining a copy of this software and associated documentation files
+ * (the "Software"), to deal in the Software without restriction,
+ * including without limitation the rights to use, copy, modify, merge,
+ * publish, distribute, sublicense, and/or sell copies of the Software,
+ * and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT.  IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
+ * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
+ * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+ * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+#ifndef TELODENDRIA_RAND_H
+#define TELODENDRIA_RAND_H
+#include <stddef.h>
+
+extern int
+ RandInt(unsigned int);
+
+extern void
+ RandIntN(int *, size_t, unsigned int);
+
+#endif                             /* TELODENDRIA_RAND_H */