optimize randint() function for massive performance increase

inc/random.h

@@ -1,6 +1,7 @@
 #ifndef RANDOM_HEADER
 #define RANDOM_HEADER
 
+void random_init(void);
 size_t randint(size_t max);
 
 #endif

src/main.c

@@ -25,6 +25,8 @@ main(void)
 {
 	system_time = 0;
 
+	random_init();
+
 	free_pages_cnt = 0;
 	busy_pages_cnt = 0;
 

src/random.c

@@ -1,14 +1,34 @@
+#include <stdio.h>
 #include <fcntl.h>
 #include <stddef.h>
 #include <unistd.h>
 
-size_t randint(size_t max)
+#define RANDOM_BUFFER_SIZE 16384
+
+static size_t index = RANDOM_BUFFER_SIZE;
+static size_t value_buff[RANDOM_BUFFER_SIZE];
+static int random_fd = -1;
+
+void
+random_init(void)
 {
-	size_t random_value;
+	random_fd = open("/dev/urandom", O_RDONLY);
 
-	int f = open("/dev/urandom", O_RDONLY);
-	read(f, &random_value, 8);
-	close(f);
-
-	return random_value % max;
+	if (random_fd < 0)
+		printf("[random:error] Failed to open /dev/urandom\n");
+}
+
+size_t
+randint(size_t max)
+{
+	if (index >= RANDOM_BUFFER_SIZE) {
+		read(random_fd, value_buff, 8 * RANDOM_BUFFER_SIZE);
+
+		index = 0;
+	}
+
+	size_t rv = value_buff[index] % max;
+	index++;
+
+	return rv;
 }