StringScanner#scan_base10_integer

static VALUE
strscan_scan_base10_integer(VALUE self)
{
    char *ptr;
    long len = 0;
    struct strscanner *p;

    GET_SCANNER(self, p);
    CLEAR_MATCH_STATUS(p);

    strscan_must_ascii_compat(p->str);

    ptr = CURPTR(p);

    long remaining_len = S_RESTLEN(p);

    if (remaining_len <= 0) {
        return Qnil;
    }

    if (ptr[len] == '-' || ptr[len] == '+') {
        len++;
    }

    if (!rb_isdigit(ptr[len])) {
        return Qnil;
    }

    MATCHED(p);
    p->prev = p->curr;

    while (len < remaining_len && rb_isdigit(ptr[len])) {
        len++;
    }

    return strscan_parse_integer(p, 10, len);
}