X-Git-Url: https://git.distorted.org.uk/u/mdw/catacomb/blobdiff_plain/ba6e6b64033b1f9de49feccb5c9cd438354481f7..0f00dc4c8eb47e67bc0f148c2dd109f73a451e0a:/math/mpmul.c

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+/* -*-c-*-
+ *
+ * Multiply many small numbers together
+ *
+ * (c) 2000 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 "mpint.h"
+#include "mpmul.h"
+
+/*----- Main code ---------------------------------------------------------*/
+
+/* --- @mpmul_init@ --- *
+ *
+ * Arguments:	@mpmul *b@ = pointer to multiplier context to initialize
+ *
+ * Returns:	---
+ *
+ * Use:		Initializes a big multiplier context for use.
+ */
+
+void mpmul_init(mpmul *b)
+{
+  b->i = 0;
+}
+
+/* --- @mpmul_add@ --- *
+ *
+ * Arguments:	@mpmul *b@ = pointer to multiplier context
+ *		@mp *x@ = the next factor to multiply in
+ *
+ * Returns:	---
+ *
+ * Use:		Contributes another factor to the mix.  It's important that
+ *		the integer lasts at least as long as the multiplication
+ *		context; this sort of rules out @mp_build@ integers.
+ */
+
+#define HWM (MPMUL_DEPTH - 20)
+#define LWM (MPMUL_DEPTH / 2)
+
+void mpmul_add(mpmul *b, mp *x)
+{
+  size_t i = b->i;
+
+  /* --- Now do the reduction step --- */
+
+  x = MP_COPY(x);
+
+  while (i > 0) {
+    if (MP_LEN(b->v[i - 1]) > MP_LEN(x))
+      break;
+    i--;
+    x = mp_mul(x, x, b->v[i]);
+    MP_DROP(b->v[i]);
+  }
+
+  if (i > HWM) {
+    while (i > LWM || (i > 0 && MP_LEN(b->v[i - 1]) <= MP_LEN(x))) {
+      i--;
+      x = mp_mul(x, x, b->v[i]);
+      MP_DROP(b->v[i]);
+    }
+  }
+
+  b->v[i++] = x;
+  b->i = i;
+}
+
+/* --- @mpmul_done@ --- *
+ *
+ * Arguments:	@mpmul *b@ = pointer to big multiplication context
+ *
+ * Returns:	The product of all the numbers contributed.
+ *
+ * Use:		Returns a (large) product of numbers.  The context is
+ *		deallocated.
+ */
+
+mp *mpmul_done(mpmul *b)
+{
+  size_t i = b->i;
+  mp *x;
+
+  if (!i)
+    return (MP_ONE);
+  i--;
+  x = b->v[i];
+  while (i > 0) {
+    i--;
+    x = mp_mul(x, x, b->v[i]);
+    MP_DROP(b->v[i]);
+  }
+  return (x);
+}
+
+/* --- @mp_factorial@ --- *
+ *
+ * Arguments:	@unsigned long i@ = number whose factorial should be
+ *			computed.
+ *
+ * Returns:	The requested factorial.
+ */
+
+mp *mp_factorial(unsigned long i)
+{
+  unsigned long j;
+  mp *x = MP_NEW;
+  mpmul b = MPMUL_INIT;
+
+  for (j = 1; j <= i; j++) {
+    x = mp_fromulong(x, j);
+    mpmul_add(&b, x);
+  }
+  mp_drop(x);
+  return (mpmul_done(&b));
+}
+
+/*----- Test rig ----------------------------------------------------------*/
+
+#ifdef TEST_RIG
+
+#include <mLib/testrig.h>
+
+static int vfact(dstr *v)
+{
+  unsigned long x = *(unsigned long *)v[0].buf;
+  mp *fx = *(mp **)v[1].buf;
+  mp *y = mp_factorial(x);
+  int ok = 1;
+  if (!MP_EQ(fx, y)) {
+    fprintf(stderr, "factorial failed\n");
+    MP_FPRINTF(stderr, (stderr, "%lu! = ", x), fx);
+    MP_EPRINT("result", y);
+    ok = 0;
+  }
+  mp_drop(fx);
+  mp_drop(y);
+  assert(mparena_count(MPARENA_GLOBAL) == 0);
+  return (ok);
+}
+
+static test_chunk tests[] = {
+  { "factorial", vfact, { &type_ulong, &type_mp, 0 } },
+  { 0, 0, { 0 } }
+};
+
+int main(int argc, char *argv[])
+{
+  test_run(argc, argv, tests, SRCDIR "/t/mp");
+  return (0);
+}
+
+#endif
+
+/*----- That's all, folks -------------------------------------------------*/