how can we git out source code base on git log?

From: loody <miloody@gmail.com>
Date: Mar 7, 2011, 17:25 UTC
Message-ID: <AANLkTimAPBoHJX0iZOt949xQ8HeGPXRyKfD4CDNJFv7u@mail.gmail.com>

Dear all: There is a paragraph in faq which told us how to git out some specific tag.

But how could I check out the source at some specific point of time if I have no idea what the tag is or there is no tag on it.

Below I use uboot for example:

commit 3831530dcb7b71329c272ccd6181f8038b6a6dd0
Author: Mikhail Zolotaryov <lebon@lebon.org.ua>
Date:   Wed Sep 8 17:06:03 2010 +0300
.......
.......

commit b75a2dde47cc0ffb686e21cbf1aea4a45e23df10
Author: Daniel Hobi <daniel.hobi@schmid-telecom.ch>
Date:   Mon Oct 11 18:03:35 2010 +0200
    tools/imls: fix comment in Makefile

Is it possible I can check out the commit as 3831530dcb7b71329c272ccd6181f8038b6a6dd0,?

Meanwhile, is there any command can help me to get the history that combine tag and commit such that I can know know the closest tag of some specific commit?

take below for example, I will know ccdd is the closest tag of commit b75a2dde47cc0ffb686e21cbf1aea4a45e23df10.

commit 3831530dcb7b71329c272ccd6181f8038b6a6dd0
Author: Mikhail Zolotaryov <lebon@lebon.org.ua>
Date:   Wed Sep 8 17:06:03 2010 +0300
.......
.......

Tag: aabb

commit b75a2dde47cc0ffb686e21cbf1aea4a45e23df10
Author: Daniel Hobi <daniel.hobi@schmid-telecom.ch>
Date:   Mon Oct 11 18:03:35 2010 +0200
    tools/imls: fix comment in Makefile
......

Tag: ccdd

-- 
Regards,

miloody