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