Mrand48_R Gnu Extension Cập Nhật Mới

mrand48_r is a function provided by the GNU C Library (glibc) that generates a sequence of pseudorandom integers using a linear congruential generator. The function is thread-safe, meaning that it can be called concurrently by multiple threads without causing race conditions or other issues.

The _r suffix in the function name indicates that it is a reentrant function, which means that it can be called safely from multiple threads or signal handlers without interference. This is achieved by providing a separate state structure for each thread or signal handler, which allows each instance of the function to maintain its own internal state without interfering with other instances.

mrand48_r is a POSIX-compliant function, meaning that it conforms to the Portable Operating System Interface (POSIX) standard. However, it is not part of the standard C library and is instead provided as a GNU extension. It is typically used in Unix-like systems, such as Linux, where it is provided by the glibc library.

To use mrand48_r, you need to provide a seed value and a pointer to a state structure, which should be initialized using the memset function. You can then call mrand48_r repeatedly to generate a sequence of pseudorandom integers.

Here’s an example usage:

c
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <stdint.h>

int main() {
    unsigned short seed[3] = {1, 2, 3};
    struct drand48_data rand_state;
    memset(&rand_state, 0, sizeof(rand_state));
    srand48_r(*(uint64_t*)seed, &rand_state);

    for (int i = 0; i < 10; i++) {
        long int rand_num;
        mrand48_r(&rand_state, &rand_num);
        printf("%ld\n", rand_num);
    }

    return 0;
}

In this example, we initialize the state structure rand_state with zeros using memset, then seed it with the values 1, 2, and 3. We then call mrand48_r repeatedly to generate a sequence of 10 pseudorandom integers, which we print to the console using printf.