Add cyclic group abstraction, with test code. Separate off exponentation

[u/mdw/catacomb] / mpbarrett-exp.c

diff --git a/mpbarrett-exp.c b/mpbarrett-exp.c
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+/* -*-c-*-
+ *
+ * $Id: mpbarrett-exp.c,v 1.1 2004/04/01 12:50:09 mdw Exp $
+ *
+ * Modular exponentiation using Barrett reduction
+ *
+ * (c) 2004 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: mpbarrett-exp.c,v $
+ * Revision 1.1  2004/04/01 12:50:09  mdw
+ * Add cyclic group abstraction, with test code.  Separate off exponentation
+ * functions for better static linking.  Fix a buttload of bugs on the way.
+ * Generally ensure that negative exponents do inversion correctly.  Add
+ * table of standard prime-field subgroups.  (Binary field subgroups are
+ * currently unimplemented but easy to add if anyone ever finds a good one.)
+ *
+ */
+
+/*----- Header files ------------------------------------------------------*/
+
+#include "mp.h"
+#include "mpbarrett.h"
+#include "mpbarrett-exp.h"
+
+/*----- Main code ---------------------------------------------------------*/
+
+/* --- @mpbarrett_exp@ --- *
+ *
+ * Arguments:  @mpbarrett *mb@ = pointer to Barrett reduction context
+ *              @mp *d@ = fake destination
+ *              @mp *a@ = base
+ *              @mp *e@ = exponent
+ *
+ * Returns:     Result, %$a^e \bmod m$%.
+ */
+
+mp *mpbarrett_exp(mpbarrett *mb, mp *d, mp *a, mp *e)
+{
+  mp *x = MP_ONE;
+  mp *spare = (e->f & MP_BURN) ? MP_NEWSEC : MP_NEW;
+
+  MP_COPY(a);
+  MP_SHRINK(e);
+  if (e->f & MP_NEG) {
+    mp *g = MP_NEW;
+    mp_gcd(&g, 0, &a, mb->m, a);
+    assert(MP_EQ(g, MP_ONE));
+    mp_drop(g);
+  }
+  if (!MP_LEN(e))
+    ;
+  else if (MP_LEN(e) < EXP_THRESH)
+    EXP_SIMPLE(x, a, e);
+  else
+    EXP_WINDOW(x, a, e);
+  mp_drop(d);
+  mp_drop(spare);
+  mp_drop(a);
+  return (x);
+}
+
+/*----- Test rig ----------------------------------------------------------*/
+
+#ifdef TEST_RIG
+
+static int vexp(dstr *v)
+{
+  mp *m = *(mp **)v[0].buf;
+  mp *a = *(mp **)v[1].buf;
+  mp *b = *(mp **)v[2].buf;
+  mp *r = *(mp **)v[3].buf;
+  mp *mr;
+  int ok = 1;
+
+  mpbarrett mb;
+  mpbarrett_create(&mb, m);
+
+  mr = mpbarrett_exp(&mb, MP_NEW, a, b);
+
+  if (!MP_EQ(mr, r)) {
+    fputs("\n*** barrett modexp failed", stderr);
+    fputs("\n m = ", stderr); mp_writefile(m, stderr, 10);
+    fputs("\n a = ", stderr); mp_writefile(a, stderr, 10);
+    fputs("\n e = ", stderr); mp_writefile(b, stderr, 10);
+    fputs("\n r = ", stderr); mp_writefile(r, stderr, 10);
+    fputs("\nmr = ", stderr); mp_writefile(mr, stderr, 10);
+    fputc('\n', stderr);
+    ok = 0;
+  }
+
+  mp_drop(m);
+  mp_drop(a);
+  mp_drop(b);
+  mp_drop(r);
+  mp_drop(mr);
+  mpbarrett_destroy(&mb);
+  assert(mparena_count(MPARENA_GLOBAL) == 0);
+  return ok;
+}
+
+static test_chunk tests[] = {
+  { "mpbarrett-exp", vexp, { &type_mp, &type_mp, &type_mp, &type_mp, 0 } },
+  { 0, 0, { 0 } }
+};
+
+int main(int argc, char *argv[])
+{
+  sub_init();
+  test_run(argc, argv, tests, SRCDIR "/tests/mpbarrett");
+  return (0);
+}
+
+#endif
+
+/*----- That's all, folks -------------------------------------------------*/