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/*
* File: random.cpp
* ----------------
* This file implements the random.h interface.
*/
#include <cstdlib>
#include <cmath>
#include <ctime>
#include "random.h"
#include "private/randompatch.h"
using namespace std;
/* Private function prototype */
static void initRandomSeed();
/*
* Implementation notes: randomInteger
* -----------------------------------
* The code for randomInteger produces the number in four steps:
*
* 1. Generate a random real number d in the range [0 .. 1).
* 2. Scale the number to the range [0 .. N) where N is the number of values.
* 3. Translate the number so that the range starts at the appropriate value.
* 4. Convert the result to the next lower integer.
*
* The implementation is complicated by the fact that both the expression
*
* RAND_MAX + 1
*
* and the expression for the number of values
*
* high - low + 1
*
* can overflow the integer range. These calculations must therefore be
* performed using doubles instead of ints.
*/
int randomInteger(int low, int high) {
initRandomSeed();
double d = rand() / (double(RAND_MAX) + 1);
double s = d * (double(high) - low + 1);
return int(floor(low + s));
}
/*
* Implementation notes: randomReal
* --------------------------------
* The code for randomReal is similar to that for randomInteger,
* without the final conversion step.
*/
double randomReal(double low, double high) {
initRandomSeed();
double d = rand() / (double(RAND_MAX) + 1);
double s = d * (high - low);
return low + s;
}
/*
* Implementation notes: randomChance
* ----------------------------------
* The code for randomChance calls randomReal(0, 1) and then checks
* whether the result is less than the requested probability.
*/
bool randomChance(double p) {
initRandomSeed();
return randomReal(0, 1) < p;
}
/*
* Implementation notes: setRandomSeed
* -----------------------------------
* The setRandomSeed function simply forwards its argument to srand.
* The call to initRandomSeed is required to set the initialized flag.
*/
void setRandomSeed(int seed) {
initRandomSeed();
srand(seed);
}
/*
* Implementation notes: initRandomSeed
* ------------------------------------
* The initRandomSeed function declares a static variable that keeps track
* of whether the seed has been initialized. The first time initRandomSeed
* is called, initialized is false, so the seed is set to the current time.
*/
static void initRandomSeed() {
static bool initialized = false;
if (!initialized) {
srand(int(time(NULL)));
initialized = true;
}
}
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