1 files changed, 106 insertions, 0 deletions
diff --git a/mpi/mpih-sub.c b/mpi/mpih-sub.c
new file mode 100644
index 000000000..3831d81c3
--- /dev/null
+++ b/mpi/mpih-sub.c
@@ -0,0 +1,106 @@
+/* mpihelp-sub.c  -  MPI helper functions
+ *	Copyright (c) 1997 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"
+
+
+/*_EXTERN_INLINE*/
+mpi_limb_t
+mpihelp_sub_1(mpi_ptr_t res_ptr,  mpi_ptr_t s1_ptr,
+	      mpi_size_t s1_size, mpi_limb_t s2_limb )
+{
+    mpi_limb_t x;
+
+    x = *s1_ptr++;
+    s2_limb = x - s2_limb;
+    *res_ptr++ = s2_limb;
+    if( s2_limb > x ) {
+	while( --s1_size ) {
+	    x = *s1_ptr++;
+	    *res_ptr++ = x - 1;
+	    if( x )
+		goto leave;
+	}
+	return 1;
+    }
+
+  leave:
+    if( res_ptr != s1_ptr ) {
+	mpi_size_t i;
+	for( i=0; i < s1_size-1; i++ )
+	    res_ptr[i] = s1_ptr[i];
+    }
+    return 0;
+}
+
+
+/* FIXME: this should be done in assembly */
+mpi_limb_t
+mpihelp_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 ? 1:0;	  /* get out carry from that addition */
+	y = x - y;		  /* main subtract */
+	cy += y > x? 1:0;	  /* get out carry from the subtract, combine */
+	res_ptr[j] = y;
+    } while( ++j );
+
+    return cy;
+}
+
+
+/*_EXTERN_INLINE*/
+mpi_limb_t
+mpihelp_sub( mpi_ptr_t res_ptr, mpi_ptr_t s1_ptr, mpi_size_t s1_size,
+				mpi_ptr_t s2_ptr, mpi_size_t s2_size)
+{
+    mpi_limb_t cy = 0;
+
+    if( s2_size )
+	cy = mpihelp_sub_n(res_ptr, s1_ptr, s2_ptr, s2_size);
+
+    if( s1_size - s2_size )
+	cy = mpihelp_sub_1(res_ptr + s2_size, s1_ptr + s2_size,
+				      s1_size - s2_size, cy);
+    return cy;
+}
+
+