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random.h

+#ifndef RANDOM_NUMBER_GENERATOR
+#define RANDOM_NUMBER_GENERATOR
+
+#include <time.h>
+
+// used to generate random number from current seed and update seed
+const unsigned long maxshort  = 65536L;
+const unsigned long multiplier = 1194211693L;
+const unsigned long adder = 12345L;
+
+class RandomNumber                              
+{
+    private:
+        // private member containing current seed
+        unsigned long randSeed;
+    public:
+        // constructor. default 0 gives automatic seeding
+        RandomNumber(unsigned long s = 0);
+        
+        // generate random integer 0 <= value <= n-1 (0到n-1内随机整数) 
+        unsigned short Random(unsigned long n);
+        
+        // generate random real number 0 <= value < 1.0 (0到1内随机实数)
+        double fRandom(void);
+};
+
+// seed the generator
+RandomNumber::RandomNumber (unsigned long s)
+{
+    if (s == 0)
+        randSeed = time(0); // Timestamp时间戳 (using system time)
+    else
+        randSeed = s;       // user supplies the seed
+}
+// return random integer 0 <= value <= n-1 < 65536
+unsigned short RandomNumber::Random (unsigned long n)
+{
+    randSeed = multiplier * randSeed + adder;
+    return (unsigned short)((randSeed >> 16)  % n);
+}
+
+// return (value in range 0..65535) / 65536
+double RandomNumber::fRandom (void)
+{
+    return Random(maxshort)/double(maxshort); 
+}
+#endif  // RANDOM_NUMBER_GENERATOR