From 4c0c155922b70b62793905490e210e9af4e3b18d Mon Sep 17 00:00:00 2001
From: Werner Koch <wk@gnupg.org>
Date: Wed, 11 Feb 1998 03:25:44 +0000
Subject: a couple of changes; but some parts are now broken

---
 mpi/mpi-mpow.c | 119 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 119 insertions(+)
 create mode 100644 mpi/mpi-mpow.c

(limited to 'mpi/mpi-mpow.c')

diff --git a/mpi/mpi-mpow.c b/mpi/mpi-mpow.c
new file mode 100644
index 000000000..5ac3c6399
--- /dev/null
+++ b/mpi/mpi-mpow.c
@@ -0,0 +1,119 @@
+/* mpi-mpow.c  -  MPI functions
+ *	Copyright (c) 1998 by Werner Koch (dd9jn)
+ *
+ * This file is part of G10.
+ *
+ * G10 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.
+ *
+ * G10 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 <config.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include "mpi-internal.h"
+#include "longlong.h"
+#include <assert.h>
+
+static int
+build_index( MPI *exparray, int k, int i, int t )
+{
+    int j, bitno;
+    int index = 0;
+
+    bitno = t-i;
+    for(j=k-1; j >= 0; j-- ) {
+	index <<= 1;
+	if( mpi_test_bit( exparray[j], bitno ) )
+	    index |= 1;
+    }
+    /*log_debug("t=%d i=%d index=%d\n", t, i, index );*/
+    return index;
+}
+
+/****************
+ * RES = (BASE[0] ^ EXP[0]) *  (BASE[1] ^ EXP[1]) * ... * mod M
+ */
+void
+mpi_mulpowm( MPI res, MPI *basearray, MPI *exparray, MPI m)
+{
+    int k;	/* number of elements */
+    int t;	/* bit size of largest exponent */
+    int i, j, idx;
+    MPI *G;	/* table with precomputed values of size 2^k */
+    MPI tmp;
+
+    for(k=0; basearray[k]; k++ )
+	;
+    assert(k);
+    for(t=0, i=0; (tmp=exparray[i]); i++ ) {
+	/*log_mpidump("exp: ", tmp );*/
+	j = mpi_get_nbits(tmp);
+	if( j > t )
+	    t = j;
+    }
+    /*log_mpidump("mod: ", m );*/
+    assert(i==k);
+    assert(t);
+    assert( k < 10 );
+
+    G = m_alloc_clear( (1<<k) * sizeof *G );
+  #if 0
+    /* do the precomputation */
+    G[0] = mpi_alloc_set_ui( 1 );
+    for(i=1; i < (1<<k); i++ ) {
+	for(j=0; j < k; j++ ) {
+	    if( (i & (1<<j) ) ) {
+		if( !G[i] )
+		    G[i] = mpi_copy( basearray[j] );
+		else
+		    mpi_mulm( G[i], G[i], basearray[j], m );
+	    }
+	}
+	if( !G[i] )
+	    G[i] = mpi_alloc(0);
+    }
+  #endif
+    /* and calculate */
+    tmp =  mpi_alloc( mpi_get_nlimbs(m)+1 );
+    mpi_set_ui( res, 1 );
+    for(i = 1; i <= t; i++ ) {
+	mpi_mulm(tmp, res, res, m );
+	idx = build_index( exparray, k, i, t );
+	assert( idx >= 0 && idx < (1<<k) );
+	if( !G[idx] ) {
+	    if( !idx )
+		 G[0] = mpi_alloc_set_ui( 1 );
+	    else {
+		for(j=0; j < k; j++ ) {
+		    if( (idx & (1<<j) ) ) {
+			if( !G[idx] )
+			    G[idx] = mpi_copy( basearray[j] );
+			else
+			    mpi_mulm( G[idx], G[idx], basearray[j], m );
+		    }
+		}
+		if( !G[idx] )
+		    G[idx] = mpi_alloc(0);
+	    }
+	}
+	mpi_mulm(res, tmp, G[idx], m );
+    }
+
+    /* cleanup */
+    m_free(tmp);
+    for(i=0; i < (1<<k); i++ )
+	mpi_free(G[i]);
+    m_free(G);
+}
+
-- 
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