Reverse a C string using bitwise XOR operator.

stringReverse.c

void stringReverse(char *str)
{
    char *p1, *p2;

    if (!str || !*str)
    {
        NSLog(@"No string passed into reverse function.");
    }
    for (p1 = str, p2 = str + strlen(str) - 1; p2 > p1; ++p1, --p2)
    {
        *p1 ^= *p2;
        *p2 ^= *p1;
        *p1 ^= *p2;
    }
}

can u please give me the explanation of line 11 12 13