Find first erring seek position

gistfile1.txt

#include <errno.h>
#include <unistd.h>
#include <stdio.h>
#include <string.h>
#include <stdint.h>
#include <sys/fcntl.h>
#include <inttypes.h>

int main()
{
        int fd = open("test", O_RDWR | O_CREAT, 0644);
        off_t st = 0;
        off_t en = INT64_MAX;
        while (st < en) {
                off_t md = ((en - st) >> 1) + st;
                if (lseek(fd, md, SEEK_SET) < 0)
                        en = md;
                else
                        st = md + 1;
        }
        printf("%" PRIx64 "", st);
}