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mpz_mul_2exp.c
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1993-05-02
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/* mpz_mul_2exp -- Multiply a bignum by 2**CNT
Copyright (C) 1991 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 General Public License as published by
the Free Software Foundation; either version 2, 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 General Public License for more details.
You should have received a copy of the GNU General Public License
along with the GNU MP Library; see the file COPYING. If not, write to
the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA. */
#include "gmp.h"
#include "gmp-impl.h"
void
#ifdef __STDC__
mpz_mul_2exp (MP_INT *w, const MP_INT *u, unsigned long int cnt)
#else
mpz_mul_2exp (w, u, cnt)
MP_INT *w;
const MP_INT *u;
unsigned long int cnt;
#endif
{
mp_size usize = u->size;
mp_size abs_usize = ABS (usize);
mp_size wsize;
mp_size limb_cnt;
mp_ptr wp;
mp_limb wdigit;
if (usize == 0)
{
w->size = 0;
return;
}
limb_cnt = cnt / BITS_PER_MP_LIMB;
wsize = abs_usize + limb_cnt + 1;
if (w->alloc < wsize)
_mpz_realloc (w, wsize);
wp = w->d;
wdigit = mpn_lshift (wp + limb_cnt, u->d, abs_usize,
cnt % BITS_PER_MP_LIMB);
wsize = abs_usize + limb_cnt;
if (wdigit != 0)
{
wp[wsize] = wdigit;
wsize++;
}
/* Zero all whole digits at low end. Do it here and not before calling
mpn_lshift, not to loose for U == W. */
MPN_ZERO (wp, limb_cnt);
w->size = (usize >= 0) ? wsize : -wsize;
}