Re: git-diff-tree inordinately (O(M*N)) slow on files with many changes

From: Davide Libenzi <davidel@xmailserver.org>
Date: Oct 16, 2006, 19:44 UTC
Message-ID: <Pine.LNX.4.64.0610161225470.7697@alien.or.mcafeemobile.com>
In-Reply-To: <Pine.LNX.4.64.0610161130090.3962@g5.osdl.org>

On Mon, 16 Oct 2006, Linus Torvalds wrote:

Show 6 quoted lines

> 
> Junio, I think this is worthy to go in before a 1.4.3 release. Possibly 
> even back-ported to earlier trees. Anything that causes an almost two 
> orders of magnitude slowdown (even if it's just on 64-bit architectures 
> and most people won't necessarily compile git that way) is worth fixing 
> pronto.

I ended up using this one:

#define XDL_HASHLONG(v, b) ((((unsigned long) (v) >> ((CHAR_BIT * sizeof(unsigned long)) - (b))) + \
                            (unsigned long) (v)) & ((1UL << (b)) - 1))

The GR_PRIME selection does not make me feel good, and the 'static inline' is puked-over by certain C compilers. It'd be probably fine to just use a simple function, though the above should work just fine.

real 0m0.665s user 0m0.655s sys 0m0.010s

(Opteron 252)

- Davide