Rearrange the file tree.

[u/mdw/catacomb] / math / mpmont-exp.c

diff --git a/math/mpmont-exp.c b/math/mpmont-exp.c
new file mode 100644 (file)
index 0000000..0ea554e
--- /dev/null
+++ b/math/mpmont-exp.c
@@ -0,0 +1,145 @@
+/* -*-c-*-
+ *
+ * Modular exponentiation with Montgomery 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 "mpmont.h"
+#include "mpmont-exp.h"
+
+/*----- Exponentiation ----------------------------------------------------*/
+
+/* --- @mpmont_expr@ --- *
+ *
+ * Arguments:  @mpmont *mm@ = pointer to Montgomery reduction context
+ *             @mp *d@ = fake destination
+ *             @mp *a@ = base
+ *             @mp *e@ = exponent
+ *
+ * Returns:    Result, %$(a R^{-1})^e R \bmod m$%.
+ */
+
+mp *mpmont_expr(mpmont *mm, mp *d, mp *a, mp *e)
+{
+  mp *x = MP_COPY(mm->r);
+  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 = mpmont_reduce(mm, a, a);
+      a = mp_modinv(a, a, mm->m);
+      a = mpmont_mul(mm, a, a, mm->r2);
+    }
+    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);
+}
+
+/* --- @mpmont_exp@ --- *
+ *
+ * Arguments:  @mpmont *mm@ = pointer to Montgomery reduction context
+ *             @mp *d@ = fake destination
+ *             @mp *a@ = base
+ *             @mp *e@ = exponent
+ *
+ * Returns:    Result, %$a^e \bmod m$%.
+ */
+
+mp *mpmont_exp(mpmont *mm, mp *d, mp *a, mp *e)
+{
+  e = MP_COPY(e);
+  d = mpmont_mul(mm, d, a, mm->r2);
+  d = mpmont_expr(mm, d, d, e);
+  d = mpmont_reduce(mm, d, d);
+  MP_DROP(e);
+  return (d);
+}
+
+/*----- Test rig ----------------------------------------------------------*/
+
+#ifdef TEST_RIG
+
+static int texp(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;
+
+  mpmont mm;
+  mpmont_create(&mm, m);
+
+  mr = mpmont_exp(&mm, MP_NEW, a, b);
+
+  if (!MP_EQ(mr, r)) {
+    fputs("\n*** montgomery 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);
+  mpmont_destroy(&mm);
+  assert(mparena_count(MPARENA_GLOBAL) == 0);
+  return ok;
+}
+
+static test_chunk tests[] = {
+  { "exp", texp, { &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/mpmont");
+  return (0);
+}
+
+#endif
+
+/*----- That's all, folks -------------------------------------------------*/