bdiff: improve worst case behavior by 100x. on 5.8MB (244.000 lines) text file with similar lines, hash before this change made diff against empty file take 75 seconds. this change improves performance to 0.6 seconds. result is that clone of smallish repo (137MB) with some files like this takes 1 minute instead of 10 minutes. common case of diff is 10% slower now, probably because of worse cache locality. but diff does not affect overall performance in common case (less than 1% of runtime is in diff when it is working ok), so this tradeoff looks good.

#!/bin/sh

mkdir test
cd test
echo foo>foo
hg init
hg addremove
hg commit -m 1
hg verify
hg serve -p 20059 -d --pid-file=hg.pid
cat hg.pid >> $DAEMON_PIDS
cd ..

http_proxy= hg clone http://localhost:20059/ copy
cd copy
hg verify
hg co
cat foo
hg manifest
hg pull