diff --git a/core/c/README b/core/c/README
index 9d306af0e..eb98c9f9c 100644
--- a/core/c/README
+++ b/core/c/README
@@ -1,4 +1,10 @@
-Prior to building the jbigi library, you will need to fetch the GMP source
+If you have a libgmp.so installed on your system already
+(check in /usr/lib), you can build a dynamically linked libjbigi.so as follows:
+	cd jbigi
+	build.sh dynamic
+The built library is jbigi/lib/libjbigi.so .
+	
+Otherwise, prior to building the jbigi library, you will need to fetch the GMP source
 from http://www.swox.com/gmp/, saving it to jbigi/gmp-4.2.2.tar.bz2 (it will
 be unpacked and built as necessary).
 
@@ -16,9 +22,12 @@ it will be used only if the router fails to load the native library.
 To build the native jbigi libraries for all supported CPUs (on the current OS),
 go into jbigi/ and run build-all.sh (the results will be under jbigi/lib/)
 
-After copying the files to the i2p/ directory,
+The build.sh script runs two speed tests, one with your existing
+I2P installation and one with the new libjbigi.
+
+Alternatively, after copying the files to the i2p/ directory,
 to run a speed test comparing the native library to the java library,
-run the shell script below.
+run the shell script below. Adjust the I2P= line as necessary.
 
 -----------------
 
diff --git a/core/c/jbigi/README b/core/c/jbigi/README
index b8417be99..56560a94f 100644
--- a/core/c/jbigi/README
+++ b/core/c/jbigi/README
@@ -1,5 +1,7 @@
 ***net.i2p.util.NativeBigInteger, native part of the code****
 
+See ../README for instructions.
+
 Execute the build.sh script to produce jbigi library files optimized for a number of different CPU-types.
 
 TODO: What is jbigi
@@ -7,7 +9,9 @@ TODO: Document generated folder structure
 TODO: Instructions for adding the libraries to a jar
 
 Linux-specific information:
-Some linux distributions comes bundled with GMP. There is currently no out-of-the-box support for this in the current build-scripts.
+Some linux distributions comes bundled with GMP.
+There is currently no out-of-the-box support for this in the current build-scripts.
 
 Windows-specific information:
-The best way of building the jbigi dll's is to install Mingw {URL} and msys {URL}. The combination of these two should be able to run the included build-scripts without modifications.
\ No newline at end of file
+The best way of building the jbigi dll's is to install Mingw {URL} and msys {URL}.
+The combination of these two should be able to run the included build-scripts without modifications.
diff --git a/core/c/jbigi/build.sh b/core/c/jbigi/build.sh
index ac563a2ba..39969b13c 100755
--- a/core/c/jbigi/build.sh
+++ b/core/c/jbigi/build.sh
@@ -1,22 +1,67 @@
 #/bin/sh
+#
+#  Build the jbigi library for i2p
+#
+#  To build a static library:
+#     download gmp-4.2.2.tar.bz2 to this directory
+#       (if a different version, change the VER= line below)
+#     build.sh
+#
+#  To build a dynamic library (you must have a libgmp.so somewhere in your system)
+#     build.sh dynamic
+#
+#  The resulting library is lib/libjbigi.so
+#
 
-VER=4.2.2
-echo "Building the jbigi library with GMP Version $VER"
-
-echo "Extracting GMP..."
-tar -xjf gmp-$VER.tar.bz2
-echo "Building..."
 mkdir -p lib/
 mkdir -p bin/local
+VER=4.2.2
+
+if [ "$1" != "dynamic" -a ! -d gmp-$VER ]
+then
+	TAR=gmp-$VER.tar.bz2
+        if [ ! -f $TAR ]
+        then
+		echo "GMP tarball $TAR not found. You must download it from http://gmplib.org/"
+		exit 1
+        fi
+
+	echo "Building the jbigi library with GMP Version $VER"
+
+	echo "Extracting GMP..."
+	tar -xjf gmp-$VER.tar.bz2
+fi
+
 cd bin/local
-case `uname -sr` in
-Darwin*)
-# --with-pic is required for static linking
-../../gmp-$VER/configure --with-pic;;
-*)
-../../gmp-$VER/configure;;
-esac
-make
-sh ../../build_jbigi.sh static
+
+echo "Building..."
+if [ "$1" != "dynamic" ]
+then
+	case `uname -sr` in
+		Darwin*)
+			# --with-pic is required for static linking
+			../../gmp-$VER/configure --with-pic;;
+		*)
+			../../gmp-$VER/configure;;
+	esac
+	make
+	sh ../../build_jbigi.sh static
+else
+	sh ../../build_jbigi.sh dynamic
+fi
+
 cp *jbigi???* ../../lib/
+echo 'Library copied to lib/'
 cd ../..
+
+I2P=~/i2p
+if [ ! -f $I2P/lib/i2p.jar ]
+then
+	echo "I2P installation not found in $I2P - correct \$I2P definition in script to run speed test"
+	exit 1
+fi
+echo 'Running test with standard I2P installation...'
+java -cp $I2P/lib/i2p.jar:$I2P/lib/jbigi.jar net.i2p.util.NativeBigInteger
+echo
+echo 'Running test with new libjbigi...'
+java -Djava.library.path=lib/ -cp $I2P/lib/i2p.jar:$I2P/lib/jbigi.jar net.i2p.util.NativeBigInteger