MPILIB: Reinstate mpi_cmp[_ui]() and export for RSA signature verification

Reinstate and export mpi_cmp() and mpi_cmp_ui() from the MPI library for use by
RSA signature verification as per RFC3447 section 5.2.2 step 1.

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

2 files changed, 71 insertions, 0 deletions

diff --git a/lib/mpi/Makefile b/lib/mpi/Makefile
index 45ca90a8639c..019a68c90144 100644
--- a/lib/mpi/Makefile
+++ b/lib/mpi/Makefile
@@ -14,6 +14,7 @@ mpi-y = \
         generic_mpih-add1.o             \
         mpicoder.o                      \
         mpi-bit.o                       \
+        mpi-cmp.o                       \
         mpih-cmp.o                      \
         mpih-div.o                      \
         mpih-mul.o                      \
diff --git a/lib/mpi/mpi-cmp.c b/lib/mpi/mpi-cmp.c
new file mode 100644
index 000000000000..1871e7b61ca0
--- /dev/null
+++ b/lib/mpi/mpi-cmp.c
@@ -0,0 +1,70 @@
+/* mpi-cmp.c  -  MPI functions
+ * Copyright (C) 1998, 1999 Free Software Foundation, Inc.
+ *
+ * This file is part of GnuPG.
+ *
+ * GnuPG is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * GnuPG is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
+ */
+
+#include "mpi-internal.h"
+
+int mpi_cmp_ui(MPI u, unsigned long v)
+{
+        mpi_limb_t limb = v;
+
+        mpi_normalize(u);
+        if (!u->nlimbs && !limb)
+                return 0;
+        if (u->sign)
+                return -1;
+        if (u->nlimbs > 1)
+                return 1;
+
+        if (u->d[0] == limb)
+                return 0;
+        else if (u->d[0] > limb)
+                return 1;
+        else
+                return -1;
+}
+EXPORT_SYMBOL_GPL(mpi_cmp_ui);
+
+int mpi_cmp(MPI u, MPI v)
+{
+        mpi_size_t usize, vsize;
+        int cmp;
+
+        mpi_normalize(u);
+        mpi_normalize(v);
+        usize = u->nlimbs;
+        vsize = v->nlimbs;
+        if (!u->sign && v->sign)
+                return 1;
+        if (u->sign && !v->sign)
+                return -1;
+        if (usize != vsize && !u->sign && !v->sign)
+                return usize - vsize;
+        if (usize != vsize && u->sign && v->sign)
+                return vsize + usize;
+        if (!usize)
+                return 0;
+        cmp = mpihelp_cmp(u->d, v->d, usize);
+        if (!cmp)
+                return 0;
+        if ((cmp < 0 ? 1 : 0) == (u->sign ? 1 : 0))
+                return 1;
+        return -1;
+}
+EXPORT_SYMBOL_GPL(mpi_cmp);