debian/patches/xdiff-Do-not-enable-XDL_FAST_HASH-by-default.diff

   1 From e8afea585132816b0024d74fc40a9294eb2afe1d Mon Sep 17 00:00:00 2001
   2 From: Anders Kaseorg <andersk@mit.edu>
   3 Date: Wed, 30 Nov 2016 23:10:53 -0500
   4 Subject: xdiff: Do not enable XDL_FAST_HASH by default
   5 MIME-Version: 1.0
   6 Content-Type: text/plain; charset=UTF-8
   7 Content-Transfer-Encoding: 8bit
   8
   9 Although XDL_FAST_HASH computes hashes slightly faster on some
  10 architectures, its collision characteristics are much worse, resulting
  11 in some pathological diffs running over 100x slower
  12 (http://public-inbox.org/git/20141222041944.GA441@peff.net/).
  13
  14 Furthermore, it was being enabled when ‘uname -m’ returns x86_64, even
  15 if we are cross-compiling for a different architecture.  This mistake
  16 was also causing the Debian build reproducibility test to fail
  17 (https://tests.reproducible-builds.org/debian/index_variations.html).
  18 Future architecture-specific definitions should be based on compiler
  19 macros such as __x86_64__ rather than uname.
  20
  21 Signed-off-by: Anders Kaseorg <andersk@mit.edu>
  22 ---
  23  Makefile         | 1 -
  24  config.mak.uname | 5 -----
  25  2 files changed, 6 deletions(-)
  26
  27 diff --git a/Makefile b/Makefile
  28 index f53fcc90d..c237d4f91 100644
  29 --- a/Makefile
  30 +++ b/Makefile
  31 @@ -341,7 +341,6 @@ all::
  32  # Define XDL_FAST_HASH to use an alternative line-hashing method in
  33  # the diff algorithm.  It gives a nice speedup if your processor has
  34  # fast unaligned word loads.  Does NOT work on big-endian systems!
  35 -# Enabled by default on x86_64.
  36  #
  37  # Define GIT_USER_AGENT if you want to change how git identifies itself during
  38  # network interactions.  The default is "git/$(GIT_VERSION)".
  39 diff --git a/config.mak.uname b/config.mak.uname
  40 index b232908f8..2831a68c3 100644
  41 --- a/config.mak.uname
  42 +++ b/config.mak.uname
  43 @@ -1,10 +1,8 @@
  44  # Platform specific Makefile tweaks based on uname detection
  45
  46  uname_S := $(shell sh -c 'uname -s 2>/dev/null || echo not')
  47 -uname_M := $(shell sh -c 'uname -m 2>/dev/null || echo not')
  48  uname_O := $(shell sh -c 'uname -o 2>/dev/null || echo not')
  49  uname_R := $(shell sh -c 'uname -r 2>/dev/null || echo not')
  50 -uname_P := $(shell sh -c 'uname -p 2>/dev/null || echo not')
  51  uname_V := $(shell sh -c 'uname -v 2>/dev/null || echo not')
  52
  53  ifdef MSVC
  54 @@ -17,9 +15,6 @@ endif
  55  # because maintaining the nesting to match is a pain.  If
  56  # we had "elif" things would have been much nicer...
  57
  58 -ifeq ($(uname_M),x86_64)
  59 -       XDL_FAST_HASH = YesPlease
  60 -endif
  61  ifeq ($(uname_S),OSF1)
  62         # Need this for u_short definitions et al
  63         BASIC_CFLAGS += -D_OSF_SOURCE
  64 --
  65 2.11.0
  66