bdiff: gradually enable the popularity hack...
bdiff: gradually enable the popularity hack
Patch from Jason Orendorff
The lower the threshold, the stronger the popularity hack's
influence. So at 3999 lines, the hack is disabled; and at 4000 lines,
the hack is enabled at maximum strength (t=4).
No source file in mercurial/crew is over 4000 lines. But there are, oh,
a few such files in Mozilla. I can testify that this hack causes hg to
generate some correct but eyebrow-raising patches.
I think the hack should phase in gradually. The threshold should be high
for small files where we don't need it so much. Like this:
t = (bn < 31000) ? 1000000 / bn : bn / 1000;
That would leave the popularity hack disabled for small files, then
gradually phase it in:
bn < 1000 -- t > bn (popularity hack is completely disabled)
bn == 1000 -- t = 1000 (still effectively disabled)
bn == 2000 -- t = 500 (only hits unusual files)
bn == 10000 -- t = 100 (only hits especially common lines)
bn == 31000 -- t = 31 (hack is at maximum power)
bn == 32000 -- t = 32 (hack could backfire, ease off)
