Import gcrypt public-key cryptography and implement signature checking.

grub-core/lib/libgcrypt/mpi/generic/mpih-sub1.c

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+/* mpihelp-add_2.c  -  MPI helper functions
+ * Copyright (C) 1994, 1996, 1997, 1998, 2001,
+ *               2002 Free Software Foundation, Inc.
+ *
+ * This file is part of Libgcrypt.
+ *
+ * Libgcrypt is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as
+ * published by the Free Software Foundation; either version 2.1 of
+ * the License, or (at your option) any later version.
+ *
+ * Libgcrypt 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 Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser 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
+ *
+ * Note: This code is heavily based on the GNU MP Library.
+ *	 Actually it's the same code with only minor changes in the
+ *	 way the data is stored; this is to support the abstraction
+ *	 of an optional secure memory allocation which may be used
+ *	 to avoid revealing of sensitive data due to paging etc.
+ */
+
+#include <config.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include "mpi-internal.h"
+#include "longlong.h"
+
+mpi_limb_t
+_gcry_mpih_sub_n( mpi_ptr_t res_ptr, mpi_ptr_t s1_ptr,
+				  mpi_ptr_t s2_ptr, mpi_size_t size)
+{
+  mpi_limb_t x, y, cy;
+  mpi_size_t j;
+
+  /* The loop counter and index J goes from -SIZE to -1.  This way
+     the loop becomes faster.  */
+  j = -size;
+
+  /* Offset the base pointers to compensate for the negative indices.  */
+  s1_ptr -= j;
+  s2_ptr -= j;
+  res_ptr -= j;
+
+  cy = 0;
+  do 
+    {
+      y = s2_ptr[j];
+      x = s1_ptr[j];
+      y += cy;		  /* add previous carry to subtrahend */
+      cy = y < cy;		  /* get out carry from that addition */
+      y = x - y;		  /* main subtract */
+      cy += y > x;		  /* get out carry from the subtract, combine */
+      res_ptr[j] = y;
+    } 
+  while( ++j );
+
+  return cy;
+}
+
+