D2626: xdiff: use xxhash in xdiff

[indygreg (Gregory Szorc)]

indygreg added a comment.


  I can reproduce the results. xxhash needs more than 4-8 bytes to outperform the old hasher. I also suspect more hash collisions are present with xxhash. Although I haven't verified.
  
  The input showing the regression effectively turns the code into a hash table benchmark.
  
  But my results on actual repo data show an improvement.
  
  FWIW, memchr+djb hash perform about the same as the original code on the perfbdiff -m case.

REPOSITORY
  rHG Mercurial

REVISION DETAIL
  https://phab.mercurial-scm.org/D2626

To: indygreg, #hg-reviewers, quark
Cc: quark, mercurial-devel