mirror of https://github.com/macssh/macssh.git
121 lines
3.3 KiB
C
Executable File
121 lines
3.3 KiB
C
Executable File
/* mpz_bin_uiui - compute n over k.
|
|
|
|
Copyright (C) 1998, 1999, 2000 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. */
|
|
|
|
#include "gmp.h"
|
|
#include "gmp-impl.h"
|
|
#include "longlong.h"
|
|
|
|
|
|
/* Avoid reallocs by rounding up any new size */
|
|
#define ROUNDUP_MASK 15
|
|
|
|
/* Enhancement: use mpn_divexact_1 when it exists */
|
|
#define MULDIV() \
|
|
MPZ_REALLOC (r, (SIZ(r)+1)|ROUNDUP_MASK); \
|
|
PTR(r)[SIZ(r)] = mpn_mul_1 (PTR(r), PTR(r), SIZ(r), nacc); \
|
|
ASSERT_NOCARRY (mpn_divrem_1 (PTR(r), (mp_size_t) 0, \
|
|
PTR(r), SIZ(r)+1, kacc)); \
|
|
SIZ(r) += (PTR(r)[SIZ(r)] != 0);
|
|
|
|
void
|
|
#if __STDC__
|
|
mpz_bin_uiui (mpz_ptr r, unsigned long int n, unsigned long int k)
|
|
#else
|
|
mpz_bin_uiui (r, n, k)
|
|
mpz_ptr r;
|
|
unsigned long int n;
|
|
unsigned long int k;
|
|
#endif
|
|
{
|
|
unsigned long int i, j;
|
|
mp_limb_t nacc, kacc;
|
|
unsigned long int cnt;
|
|
|
|
/* bin(n,k) = 0 if k>n. */
|
|
if (n < k)
|
|
{
|
|
mpz_set_ui (r, 0);
|
|
return;
|
|
}
|
|
|
|
/* Rewrite bin(n,k) as bin(n,n-k) if that is smaller. */
|
|
k = MIN (k, n-k);
|
|
|
|
/* bin(n,0) = 1 */
|
|
if (k == 0)
|
|
{
|
|
mpz_set_ui (r, 1);
|
|
return;
|
|
}
|
|
|
|
j = n - k + 1;
|
|
mpz_set_ui (r, j);
|
|
|
|
/* Initialize accumulators. */
|
|
nacc = 1;
|
|
kacc = 1;
|
|
|
|
cnt = 0;
|
|
for (i = 2; i <= k; i++)
|
|
{
|
|
mp_limb_t n1, n0, k1, k0;
|
|
|
|
j++;
|
|
#if 0
|
|
/* Remove common multiples of 2. This will allow us to accumulate
|
|
more in nacc and kacc before we need a bignum step. It would make
|
|
sense to cancel factors of 3, 5, etc too, but this would be best
|
|
handled by sieving out factors. Alternatively, we could perform a
|
|
gcd of the accumulators just as they have overflown, and keep
|
|
accumulating until the gcd doesn't remove a significant factor. */
|
|
while (((nacc | kacc) & 1) == 0)
|
|
{
|
|
nacc >>= 1;
|
|
kacc >>= 1;
|
|
}
|
|
#else
|
|
cnt = ((nacc | kacc) & 1) ^ 1;
|
|
nacc >>= cnt;
|
|
kacc >>= cnt;
|
|
#endif
|
|
/* Accumulate next multiples. */
|
|
umul_ppmm (n1, n0, nacc, j);
|
|
umul_ppmm (k1, k0, kacc, i);
|
|
if (n1 != 0)
|
|
{
|
|
/* Accumulator overflow. Perform bignum step. */
|
|
MULDIV ();
|
|
nacc = j;
|
|
kacc = i;
|
|
}
|
|
else
|
|
{
|
|
if (k1 != 0) abort ();
|
|
/* Save new products in accumulators to keep accumulating. */
|
|
nacc = n0;
|
|
kacc = k0;
|
|
}
|
|
}
|
|
|
|
/* Take care of whatever is left in accumulators. */
|
|
MULDIV ();
|
|
}
|