+++ /dev/null
-/* 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
-}
projects / ghc-hetmet.git / blobdiff