New generic exponentation code. Includes sliding-window simultaneous

[u/mdw/catacomb] / exp.c

diff --git a/exp.c b/exp.c
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+/* -*-c-*-
+ *
+ * $Id: exp.c,v 1.1 2001/06/16 13:00:59 mdw Exp $
+ *
+ * Generalized exponentiation
+ *
+ * (c) 2001 Straylight/Edgeware
+ */
+
+/*----- Licensing notice --------------------------------------------------* 
+ *
+ * This file is part of Catacomb.
+ *
+ * Catacomb is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Library General Public License as
+ * published by the Free Software Foundation; either version 2 of the
+ * License, or (at your option) any later version.
+ * 
+ * Catacomb 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 Library General Public License for more details.
+ * 
+ * You should have received a copy of the GNU Library General Public
+ * License along with Catacomb; if not, write to the Free
+ * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
+ * MA 02111-1307, USA.
+ */
+
+/*----- Revision history --------------------------------------------------* 
+ *
+ * $Log: exp.c,v $
+ * Revision 1.1  2001/06/16 13:00:59  mdw
+ * New generic exponentation code.  Includes sliding-window simultaneous
+ * exponentiation.
+ *
+ */
+
+/*----- Header files ------------------------------------------------------*/
+
+#define EXP_TYPE /* Hack */
+#include "exp.h"
+
+/*----- Main code ---------------------------------------------------------*/
+
+/* --- @exp_simulnext@ --- *
+ *
+ * Arguments:  @exp_simul *e@ = pointer to state structure
+ *             @size_t x@ = a current accumulator
+ *
+ * Returns:    The next column of bits.
+ *
+ * Use:                Scans the next column of bits for a simultaneous
+ *             exponentiation.
+ */
+
+size_t exp_simulnext(exp_simul *e, size_t x)
+{
+  size_t i;
+
+  /* --- Move to the next word along --- */
+
+  if (!e->b) {
+    e->o--;
+    for (i = 0; i < e->n; i++)
+      e->s[i].w = e->o < e->s[i].len ? e->s[i].v[e->o] : 0;
+    e->b = MPW_BITS;
+  }
+
+  /* --- Scan out a column of bits --- */
+
+  for (i = 0; i < e->n; i++) {
+    x = (x << 1) | ((e->s[i].w >> (MPW_BITS - 1)) & 1u);
+    e->s[i].w <<= 1;
+  }      
+  e->b--;
+  return (x);
+}
+
+/*----- That's all, folks -------------------------------------------------*/