build: Add --enable-pointer-packing option.

Pointer packing is now disabled by default for x86_64 targets.
Jeffrey M. Birnbaum <jmbny.@...> told me that according to his
discussions with Intel engineers, Haswell will be bumping up
VMA bits to 56 bits from 48.

If you control the hardware that CK is deployed to and don't
envision a migration to 48-bits anytime soon, then you may
enable old behavior (resulting in significant memory savings
for some data structures, namely ck_ht) by passing the
--enable-pointer-packing flag to configure.

configure

@@ -91,6 +91,7 @@ generate()
 	    -e "s#@MANDIR@#$MANDIR#g"				\
 	    -e "s#@GZIP@#$GZIP#g"				\
 	    -e "s#@GZIP_SUFFIX@#$GZIP_SUFFIX#g"			\
+	    -e "s#@POINTER_PACK_ENABLE@#$POINTER_PACK_ENABLE#g"			\
 		$1 > $2
 }
 
@@ -106,6 +107,7 @@ generate_stdout()
 	echo "                LD = $LD"
 	echo "           LDFLAGS = $LDFLAGS"
 	echo "              GZIP = $GZIP"
+	echo "      POINTER_PACK = $POINTER_PACK_ENABLE"
 	echo
 	echo "Headers will be installed in $HEADERS"
 	echo "Libraries will be installed in $LIBRARY"
@@ -127,6 +129,7 @@ for option in $*; do
 		echo "  --libdir=N               Libraries directory (default is ${PREFIX}/lib)"
 		echo "  --mandir=N               Manual pages directory (default is ${PREFIX}/man)"
 		echo "  --prefix=N               Installs library files in N (default is $PREFIX)"
+		echo "  --enable-pointer-packing Assumes 48-bit address encoding"
 		echo
 		echo "The following environment variables may be used:"
 		echo "   CC       C compiler command"
@@ -137,6 +140,9 @@ for option in $*; do
 		echo "Report bugs to ${MAINTAINER}."
 		exit $EXIT_SUCCESS
 		;;
+	--enable-pointer-packing)
+		POINTER_PACK_ENABLE="CK_MD_POINTER_PACK_ENABLE"
+		;;
 	--profile=*)
 		PROFILE=$value
 		;;
@@ -163,6 +169,7 @@ HEADERS=${HEADERS:-"${PREFIX}/include"}
 LIBRARY=${LIBRARY:-"${PREFIX}/lib"}
 MANDIR=${MANDIR:-"${PREFIX}/share/man"}
 GZIP=${GZIP:-"gzip -c"}
+POINTER_PACK_ENABLE=${POINTER_PACK_ENABLE:-"CK_MD_POINTER_PACK_DISABLE"}
 
 if test "$PROFILE"; then
 	printf "Using user-specified profile....."
@@ -178,6 +185,9 @@ if test "$PROFILE"; then
 	fi
 
 	echo "success [$PROFILE]"
+	printf "Generating header files.........."
+	generate include/ck_md.h.in include/ck_md.h
+	echo "success"
 	printf "Generating build files..........."
 	generate doc/Makefile.in doc/Makefile
 	generate build/ck.build.in build/ck.build
@@ -418,6 +428,10 @@ EOF
 	fi
 done
 
+printf "Generating header files.........."
+generate include/ck_md.h.in include/ck_md.h
+echo "success"
+
 printf "Generating build files..........."
 
 generate doc/Makefile.in doc/Makefile

include/ck_md.h.in

@@ -35,4 +35,8 @@
 #define CK_MD_PAGESIZE (4096)
 #endif
 
+#ifndef @POINTER_PACK_ENABLE@
+#define @POINTER_PACK_ENABLE@
+#endif
+
 #endif /* _CK_MD_H */