add lab answers

labcodes_answer/lab5_result/libs/rand.c

@@ -0,0 +1,26 @@
+#include <x86.h>
+#include <stdlib.h>
+
+static unsigned long long next = 1;
+
+/* *
+ * rand - returns a pseudo-random integer
+ *
+ * The rand() function return a value in the range [0, RAND_MAX].
+ * */
+int
+rand(void) {
+    next = (next * 0x5DEECE66DLL + 0xBLL) & ((1LL << 48) - 1);
+    unsigned long long result = (next >> 12);
+    return (int)do_div(result, RAND_MAX + 1);
+}
+
+/* *
+ * srand - seed the random number generator with the given number
+ * @seed:   the required seed number
+ * */
+void
+srand(unsigned int seed) {
+    next = seed;
+}
+