diff --git a/include/cryb/mpi.h b/include/cryb/mpi.h
index 84c7bf3..863e413 100644
--- a/include/cryb/mpi.h
+++ b/include/cryb/mpi.h
@@ -49,7 +49,9 @@ const char *cryb_mpi_version(void);
 #define mpi_grow		cryb_mpi_grow
 #define mpi_init		cryb_mpi_init
 #define mpi_load		cryb_mpi_load
+#define mpi_lsb			cryb_mpi_lsb
 #define mpi_lshift		cryb_mpi_lshift
+#define mpi_msb			cryb_mpi_msb
 #define mpi_negate		cryb_mpi_negate
 #define mpi_rshift		cryb_mpi_rshift
 #define mpi_set			cryb_mpi_set
@@ -80,6 +82,8 @@ int mpi_copy(cryb_mpi *, const cryb_mpi *);
 void mpi_swap(cryb_mpi *, cryb_mpi *);
 int mpi_load(cryb_mpi *, const uint8_t *, size_t);
 int mpi_set(cryb_mpi *, int32_t);
+unsigned int mpi_lsb(const cryb_mpi *);
+unsigned int mpi_msb(const cryb_mpi *);
 int mpi_lshift(cryb_mpi *, unsigned int);
 int mpi_rshift(cryb_mpi *, unsigned int);
 int mpi_add_abs(cryb_mpi *, const cryb_mpi *, const cryb_mpi *);
diff --git a/lib/mpi/Makefile.am b/lib/mpi/Makefile.am
index d6dfb13..c645d86 100644
--- a/lib/mpi/Makefile.am
+++ b/lib/mpi/Makefile.am
@@ -14,7 +14,9 @@ libcryb_mpi_la_SOURCES = \
 	cryb_mpi_grow.c \
 	cryb_mpi_init.c \
 	cryb_mpi_load.c \
+	cryb_mpi_lsb.c \
 	cryb_mpi_lshift.c \
+	cryb_mpi_msb.c \
 	cryb_mpi_negate.c \
 	cryb_mpi_rshift.c \
 	cryb_mpi_set.c \
diff --git a/lib/mpi/cryb_mpi_lsb.c b/lib/mpi/cryb_mpi_lsb.c
new file mode 100644
index 0000000..13f94e4
--- /dev/null
+++ b/lib/mpi/cryb_mpi_lsb.c
@@ -0,0 +1,54 @@
+/*
+ * Copyright (c) 2017 Dag-Erling Smørgrav
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. The name of the author may not be used to endorse or promote
+ *    products derived from this software without specific prior written
+ *    permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include "cryb/impl.h"
+
+#include <stddef.h>
+#include <stdint.h>
+
+#include <cryb/mpi.h>
+
+#include "cryb_mpi_impl.h"
+
+/*
+ * Return the 1-based index of the least significant bit of X
+ */
+unsigned int
+mpi_lsb(const cryb_mpi *X)
+{
+	unsigned int lsw, lsb;
+
+	if (X->msb == 0)
+		return (0);
+	for (lsw = 0; X->words[lsw] == 0; ++lsw)
+		/* nothing */ ;
+	for (lsb = 0; (X->words[lsw] & (1 << lsb)) == 0; ++lsb)
+		/* nothing */ ;
+	return (lsw * 32 + lsb + 1);
+}
diff --git a/lib/mpi/cryb_mpi_msb.c b/lib/mpi/cryb_mpi_msb.c
new file mode 100644
index 0000000..72a91e4
--- /dev/null
+++ b/lib/mpi/cryb_mpi_msb.c
@@ -0,0 +1,47 @@
+/*
+ * Copyright (c) 2017 Dag-Erling Smørgrav
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. The name of the author may not be used to endorse or promote
+ *    products derived from this software without specific prior written
+ *    permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include "cryb/impl.h"
+
+#include <stddef.h>
+#include <stdint.h>
+
+#include <cryb/mpi.h>
+
+#include "cryb_mpi_impl.h"
+
+/*
+ * Return the 1-based index of the most significant bit of X
+ */
+unsigned int
+mpi_msb(const cryb_mpi *X)
+{
+
+	return (X->msb);
+}