string_expandtabs(PyStringObject *self, PyObject *args)
{
    const char *e, *p, *qe;
    char *q;
    Py_ssize_t i, j, incr;
    PyObject *u;
    int tabsize = 8;

    if (!PyArg_ParseTuple(args, "|i:expandtabs", &tabsize))
        return NULL;

    /* First pass: determine size of output string */
    i = 0; /* chars up to and including most recent \n or \r */
    j = 0; /* chars since most recent \n or \r (use in tab calculations) */
    e = PyString_AS_STRING(self) + PyString_GET_SIZE(self); /* end of input */
    for (p = PyString_AS_STRING(self); p < e; p++) {
        if (*p == '\t') {
            if (tabsize > 0) {
                incr = tabsize - (j % tabsize);
                if (j > PY_SSIZE_T_MAX - incr)
                    goto overflow1;
                j += incr;
            }
        }
        else {
            if (j > PY_SSIZE_T_MAX - 1)
                goto overflow1;
            j++;
            if (*p == '\n' || *p == '\r') {
                if (i > PY_SSIZE_T_MAX - j)
                    goto overflow1;
                i += j;
                j = 0;
            }
        }
    }

    if (i > PY_SSIZE_T_MAX - j)
        goto overflow1;

    /* Second pass: create output string and fill it */
    u = PyString_FromStringAndSize(NULL, i + j);
    if (!u)
        return NULL;

    j = 0; /* same as in first pass */
    q = PyString_AS_STRING(u); /* next output char */
    qe = PyString_AS_STRING(u) + PyString_GET_SIZE(u); /* end of output */

    for (p = PyString_AS_STRING(self); p < e; p++) {
        if (*p == '\t') {
            if (tabsize > 0) {
                i = tabsize - (j % tabsize);
                j += i;
                while (i--) {
                    if (q >= qe)
                        goto overflow2;
                    *q++ = ' ';
                }
            }
        }
        else {
            if (q >= qe)
                goto overflow2;
            *q++ = *p;
            j++;
            if (*p == '\n' || *p == '\r')
                j = 0;
        }
    }

    return u;

  overflow2:
    Py_DECREF(u);
  overflow1:
    PyErr_SetString(PyExc_OverflowError, "new string is too long");
    return NULL;
}
Unknown