freebsd-dev/contrib/libgmp/mpz/mul_2exp.c

77 lines
1.9 KiB
C
Raw Normal View History

/* mpz_mul_2exp -- Multiply a bignum by 2**CNT
Copyright (C) 1991, 1993, 1994, 1996 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 Library General Public License as published by
the Free Software Foundation; either version 2 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 Library General Public
License for more details.
You should have received a copy of the GNU Library 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"
void
#if __STDC__
mpz_mul_2exp (mpz_ptr w, mpz_srcptr u, unsigned long int cnt)
#else
mpz_mul_2exp (w, u, cnt)
mpz_ptr w;
mpz_srcptr u;
unsigned long int cnt;
#endif
{
mp_size_t usize = u->_mp_size;
mp_size_t abs_usize = ABS (usize);
mp_size_t wsize;
mp_size_t limb_cnt;
mp_ptr wp;
mp_limb_t wlimb;
if (usize == 0)
{
w->_mp_size = 0;
return;
}
limb_cnt = cnt / BITS_PER_MP_LIMB;
wsize = abs_usize + limb_cnt + 1;
if (w->_mp_alloc < wsize)
_mpz_realloc (w, wsize);
wp = w->_mp_d;
wsize = abs_usize + limb_cnt;
cnt %= BITS_PER_MP_LIMB;
if (cnt != 0)
{
wlimb = mpn_lshift (wp + limb_cnt, u->_mp_d, abs_usize, cnt);
if (wlimb != 0)
{
wp[wsize] = wlimb;
wsize++;
}
}
else
{
MPN_COPY_DECR (wp + limb_cnt, u->_mp_d, abs_usize);
}
/* Zero all whole limbs at low end. Do it here and not before calling
mpn_lshift, not to lose for U == W. */
MPN_ZERO (wp, limb_cnt);
w->_mp_size = usize >= 0 ? wsize : -wsize;
}