question about tzload's buffer size

[Paul Eggert]

In this code:

        union {
                struct tzhead   tzhead;
                char            buf[2 * sizeof(struct tzhead) +
                                        2 * sizeof *sp +
                                        4 * TZ_MAX_TIMES];
        } u;

it's not clear to me that the buffer is large enough.  For example,
aren't there two copies of the leap second transitions, and isn't the
second copy bigger, so shouldn't TZ_MAX_LEAPS be involved?  And is
there guaranteed to be room for the POSIX TZ string?

Perhaps a comment is in order, at any rate?