+/* -*-c-*-
+ *
+ * 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.
+ */
+
+/*----- 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 (MP_ZEROP(e))
+ ;
+ else {
+ if (MP_NEGP(e))
+ a = mp_modinv(a, a, mb->m);
+ 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 "/t/mpbarrett");
+ return (0);
+}
+
+#endif
+
+/*----- That's all, folks -------------------------------------------------*/