X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=rts%2Fgmp%2Fmpz%2Ffac_ui.c;fp=rts%2Fgmp%2Fmpz%2Ffac_ui.c;h=85f40f271ca64382c6356cef458a2ad60087e719;hb=0065d5ab628975892cea1ec7303f968c3338cbe1;hp=0000000000000000000000000000000000000000;hpb=28a464a75e14cece5db40f2765a29348273ff2d2;p=ghc-hetmet.git

diff --git a/rts/gmp/mpz/fac_ui.c b/rts/gmp/mpz/fac_ui.c
new file mode 100644
index 0000000..85f40f2
--- /dev/null
+++ b/rts/gmp/mpz/fac_ui.c
@@ -0,0 +1,157 @@
+/* mpz_fac_ui(result, n) -- Set RESULT to N!.
+
+Copyright (C) 1991, 1993, 1994, 1995 Free Software Foundation, Inc.
+
+This file is part of the GNU MP Library.
+
+The GNU MP Library is free software; you can redistribute it and/or modify
+it under the terms of the GNU Lesser General Public License as published by
+the Free Software Foundation; either version 2.1 of the License, or (at your
+option) any later version.
+
+The GNU MP Library 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 Lesser General Public
+License for more details.
+
+You should have received a copy of the GNU Lesser General Public License
+along with the GNU MP Library; see the file COPYING.LIB.  If not, write to
+the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
+MA 02111-1307, USA. */
+
+#ifdef DBG
+#include <stdio.h>
+#endif
+
+#include "gmp.h"
+#include "gmp-impl.h"
+#include "longlong.h"
+
+void
+#if __STDC__
+mpz_fac_ui (mpz_ptr result, unsigned long int n)
+#else
+mpz_fac_ui (result, n)
+     mpz_ptr result;
+     unsigned long int n;
+#endif
+{
+#if SIMPLE_FAC
+
+  /* Be silly.  Just multiply the numbers in ascending order.  O(n**2).  */
+
+  unsigned long int k;
+
+  mpz_set_ui (result, 1L);
+
+  for (k = 2; k <= n; k++)
+    mpz_mul_ui (result, result, k);
+#else
+
+  /* Be smarter.  Multiply groups of numbers in ascending order until the
+     product doesn't fit in a limb.  Multiply these partial product in a
+     balanced binary tree fashion, to make the operand have as equal sizes
+     as possible.  When the operands have about the same size, mpn_mul
+     becomes faster.  */
+
+  unsigned long int p, k;
+  mp_limb_t p1, p0;
+
+  /* Stack of partial products, used to make the computation balanced
+     (i.e. make the sizes of the multiplication operands equal).  The
+     topmost position of MP_STACK will contain a one-limb partial product,
+     the second topmost will contain a two-limb partial product, and so
+     on.  MP_STACK[0] will contain a partial product with 2**t limbs.
+     To compute n! MP_STACK needs to be less than
+     log(n)**2/log(BITS_PER_MP_LIMB), so 30 is surely enough.  */
+#define MP_STACK_SIZE 30
+  mpz_t mp_stack[MP_STACK_SIZE];
+
+  /* TOP is an index into MP_STACK, giving the topmost element.
+     TOP_LIMIT_SO_FAR is the largets value it has taken so far.  */
+  int top, top_limit_so_far;
+
+  /* Count of the total number of limbs put on MP_STACK so far.  This
+     variable plays an essential role in making the compututation balanced.
+     See below.  */
+  unsigned int tree_cnt;
+
+  top = top_limit_so_far = -1;
+  tree_cnt = 0;
+  p = 1;
+  for (k = 2; k <= n; k++)
+    {
+      /* Multiply the partial product in P with K.  */
+      umul_ppmm (p1, p0, (mp_limb_t) p, (mp_limb_t) k);
+
+      /* Did we get overflow into the high limb, i.e. is the partial
+	 product now more than one limb?  */
+      if (p1 != 0)
+	{
+	  tree_cnt++;
+
+	  if (tree_cnt % 2 == 0)
+	    {
+	      mp_size_t i;
+
+	      /* TREE_CNT is even (i.e. we have generated an even number of
+		 one-limb partial products), which means that we have a
+		 single-limb product on the top of MP_STACK.  */
+
+	      mpz_mul_ui (mp_stack[top], mp_stack[top], p);
+
+	      /* If TREE_CNT is divisable by 4, 8,..., we have two
+		 similar-sized partial products with 2, 4,... limbs at
+		 the topmost two positions of MP_STACK.  Multiply them
+		 to form a new partial product with 4, 8,... limbs.  */
+	      for (i = 4; (tree_cnt & (i - 1)) == 0; i <<= 1)
+		{
+		  mpz_mul (mp_stack[top - 1],
+			   mp_stack[top], mp_stack[top - 1]);
+		  top--;
+		}
+	    }
+	  else
+	    {
+	      /* Put the single-limb partial product in P on the stack.
+		 (The next time we get a single-limb product, we will
+		 multiply the two together.)  */
+	      top++;
+	      if (top > top_limit_so_far)
+		{
+		  if (top > MP_STACK_SIZE)
+		    abort();
+		  /* The stack is now bigger than ever, initialize the top
+		     element.  */
+		  mpz_init_set_ui (mp_stack[top], p);
+		  top_limit_so_far++;
+		}
+	      else
+		mpz_set_ui (mp_stack[top], p);
+	    }
+
+	  /* We ignored the last result from umul_ppmm.  Put K in P as the
+	     first component of the next single-limb partial product.  */
+	  p = k;
+	}
+      else
+	/* We didn't get overflow in umul_ppmm.  Put p0 in P and try
+	   with one more value of K.  */
+	p = p0;			/* bogus if long != mp_limb_t */
+    }
+
+  /* We have partial products in mp_stack[0..top], in descending order.
+     We also have a small partial product in p.
+     Their product is the final result.  */
+  if (top < 0)
+    mpz_set_ui (result, p);
+  else
+    mpz_mul_ui (result, mp_stack[top--], p);
+  while (top >= 0)
+    mpz_mul (result, result, mp_stack[top--]);
+
+  /* Free the storage allocated for MP_STACK.  */
+  for (top = top_limit_so_far; top >= 0; top--)
+    mpz_clear (mp_stack[top]);
+#endif
+}