tz

#include <time.h>

/*
$ gcc -Wall -O3 time.c -o time
$ time ./time

real    0m7.102s
user    0m2.060s
sys     0m5.040s
$ time TZ=:/etc/localtime ./time

real    0m0.952s
user    0m0.948s
sys     0m0.000s
*/

int main(int argc, char *argv[])
{
        int i = 0;
        time_t timep;

        for (i = 0; i < 10000000; i++) {
                time(&timep);
                localtime(&timep);
        }

        return 0;
}