absurdly slow git-diff

[Abhijit Menon-Sen <ams@toroid.org>]

I have a 240k-line file, and I change one character on every sixth line.
The resulting diff gives git serious indigestion:

$ git --version
git version 1.6.0.3.640.g6331a
$ mkdir a; cd a; git init
Initialized empty Git repository in /home/ams/a/.git/
$ cp ../1 .; git add 1; git commit -q -m 1
$ cp ../2 1; git add 1; git commit -q -m 2 
$ time git show HEAD > x
git show HEAD > x  309.88s user 0.46s system 97% cpu 5:17.06 total

(I use commit -q above not only for brevity; for the second commit,
calculating the diffstat takes the same five minutes that git show,
git log -p, git log --stat etc. all take.)

Note that diff(1) can handle the patch fine:

$ time diff -u ../1 ../2 >/dev/null
diff -u ../1 ../2 > /dev/null  0.30s user 0.06s system 69% cpu 0.519 total

If anyone's interested, the files are http://toroid.org/misc/1 and
http://toroid.org/misc/2

Does anyone understand why this slowdown might happen or have
suggestions about where I should look for it?

Thanks.

-- ams