Annotation of OpenXM_contrib/gmp/mpz/bin_uiui.c, Revision 1.1.1.1
1.1 maekawa 1: /* mpz_bin_uiui - compute n over k.
2:
3: Copyright (C) 1998, 1999, 2000 Free Software Foundation, Inc.
4:
5: This file is part of the GNU MP Library.
6:
7: The GNU MP Library is free software; you can redistribute it and/or modify
8: it under the terms of the GNU Lesser General Public License as published by
9: the Free Software Foundation; either version 2.1 of the License, or (at your
10: option) any later version.
11:
12: The GNU MP Library is distributed in the hope that it will be useful, but
13: WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
14: or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
15: License for more details.
16:
17: You should have received a copy of the GNU Lesser General Public License
18: along with the GNU MP Library; see the file COPYING.LIB. If not, write to
19: the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
20: MA 02111-1307, USA. */
21:
22: #include "gmp.h"
23: #include "gmp-impl.h"
24: #include "longlong.h"
25:
26:
27: /* Avoid reallocs by rounding up any new size */
28: #define ROUNDUP_MASK 15
29:
30: /* Enhancement: use mpn_divexact_1 when it exists */
31: #define MULDIV() \
32: MPZ_REALLOC (r, (SIZ(r)+1)|ROUNDUP_MASK); \
33: PTR(r)[SIZ(r)] = mpn_mul_1 (PTR(r), PTR(r), SIZ(r), nacc); \
34: ASSERT_NOCARRY (mpn_divrem_1 (PTR(r), (mp_size_t) 0, \
35: PTR(r), SIZ(r)+1, kacc)); \
36: SIZ(r) += (PTR(r)[SIZ(r)] != 0);
37:
38: void
39: #if __STDC__
40: mpz_bin_uiui (mpz_ptr r, unsigned long int n, unsigned long int k)
41: #else
42: mpz_bin_uiui (r, n, k)
43: mpz_ptr r;
44: unsigned long int n;
45: unsigned long int k;
46: #endif
47: {
48: unsigned long int i, j;
49: mp_limb_t nacc, kacc;
50: unsigned long int cnt;
51:
52: /* bin(n,k) = 0 if k>n. */
53: if (n < k)
54: {
55: mpz_set_ui (r, 0);
56: return;
57: }
58:
59: /* Rewrite bin(n,k) as bin(n,n-k) if that is smaller. */
60: k = MIN (k, n-k);
61:
62: /* bin(n,0) = 1 */
63: if (k == 0)
64: {
65: mpz_set_ui (r, 1);
66: return;
67: }
68:
69: j = n - k + 1;
70: mpz_set_ui (r, j);
71:
72: /* Initialize accumulators. */
73: nacc = 1;
74: kacc = 1;
75:
76: cnt = 0;
77: for (i = 2; i <= k; i++)
78: {
79: mp_limb_t n1, n0, k1, k0;
80:
81: j++;
82: #if 0
83: /* Remove common multiples of 2. This will allow us to accumulate
84: more in nacc and kacc before we need a bignum step. It would make
85: sense to cancel factors of 3, 5, etc too, but this would be best
86: handled by sieving out factors. Alternatively, we could perform a
87: gcd of the accumulators just as they have overflown, and keep
88: accumulating until the gcd doesn't remove a significant factor. */
89: while (((nacc | kacc) & 1) == 0)
90: {
91: nacc >>= 1;
92: kacc >>= 1;
93: }
94: #else
95: cnt = ((nacc | kacc) & 1) ^ 1;
96: nacc >>= cnt;
97: kacc >>= cnt;
98: #endif
99: /* Accumulate next multiples. */
100: umul_ppmm (n1, n0, nacc, j);
101: umul_ppmm (k1, k0, kacc, i);
102: if (n1 != 0)
103: {
104: /* Accumulator overflow. Perform bignum step. */
105: MULDIV ();
106: nacc = j;
107: kacc = i;
108: }
109: else
110: {
111: if (k1 != 0) abort ();
112: /* Save new products in accumulators to keep accumulating. */
113: nacc = n0;
114: kacc = k0;
115: }
116: }
117:
118: /* Take care of whatever is left in accumulators. */
119: MULDIV ();
120: }
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