sha1dc: allow building with the external sha1dc library

diff --git a/Makefile b/Makefile
index 5e7e9022bdd81d270a7a7af95d3677cb91406a35..9f492b5d1d37fa3621d45ab7292dd1b3a28b0b63 100644 (file)
--- a/Makefile
+++ b/Makefile
@@ -162,6 +162,11 @@ all::
 # algorithm. This is slower, but may detect attempted collision attacks.
 # Takes priority over other *_SHA1 knobs.
 #
+# Define DC_SHA1_EXTERNAL in addition to DC_SHA1 if you want to build / link
+# git with the external SHA1 collision-detect library.
+# Without this option, i.e. the default behavior is to build git with its
+# own built-in code (or submodule).
+#
 # Define DC_SHA1_SUBMODULE in addition to DC_SHA1 to use the
 # sha1collisiondetection shipped as a submodule instead of the
 # non-submodule copy in sha1dc/. This is an experimental option used
@@ -1474,6 +1479,13 @@ else
        DC_SHA1 := YesPlease
        BASIC_CFLAGS += -DSHA1_DC
        LIB_OBJS += sha1dc_git.o
+ifdef DC_SHA1_EXTERNAL
+       ifdef DC_SHA1_SUBMODULE
+$(error Only set DC_SHA1_EXTERNAL or DC_SHA1_SUBMODULE, not both)
+       endif
+       BASIC_CFLAGS += -DDC_SHA1_EXTERNAL
+       EXTLIBS += -lsha1detectcoll
+else
 ifdef DC_SHA1_SUBMODULE
        LIB_OBJS += sha1collisiondetection/lib/sha1.o
        LIB_OBJS += sha1collisiondetection/lib/ubc_check.o
@@ -1491,6 +1503,7 @@ endif
 endif
 endif
 endif
+endif
 
 ifdef SHA1_MAX_BLOCK_SIZE
        LIB_OBJS += compat/sha1-chunked.o