77 lines
1.9 KiB
C
77 lines
1.9 KiB
C
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/* mpz_mul_2exp -- Multiply a bignum by 2**CNT
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Copyright (C) 1991, 1993, 1994, 1996 Free Software Foundation, Inc.
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This file is part of the GNU MP Library.
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The GNU MP Library is free software; you can redistribute it and/or modify
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it under the terms of the GNU Library General Public License as published by
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the Free Software Foundation; either version 2 of the License, or (at your
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option) any later version.
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The GNU MP Library is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
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or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Library General Public
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License for more details.
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You should have received a copy of the GNU Library General Public License
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along with the GNU MP Library; see the file COPYING.LIB. If not, write to
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the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
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MA 02111-1307, USA. */
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#include "gmp.h"
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#include "gmp-impl.h"
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void
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#if __STDC__
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mpz_mul_2exp (mpz_ptr w, mpz_srcptr u, unsigned long int cnt)
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#else
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mpz_mul_2exp (w, u, cnt)
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mpz_ptr w;
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mpz_srcptr u;
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unsigned long int cnt;
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#endif
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{
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mp_size_t usize = u->_mp_size;
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mp_size_t abs_usize = ABS (usize);
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mp_size_t wsize;
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mp_size_t limb_cnt;
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mp_ptr wp;
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mp_limb_t wlimb;
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if (usize == 0)
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{
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w->_mp_size = 0;
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return;
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}
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limb_cnt = cnt / BITS_PER_MP_LIMB;
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wsize = abs_usize + limb_cnt + 1;
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if (w->_mp_alloc < wsize)
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_mpz_realloc (w, wsize);
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wp = w->_mp_d;
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wsize = abs_usize + limb_cnt;
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cnt %= BITS_PER_MP_LIMB;
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if (cnt != 0)
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{
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wlimb = mpn_lshift (wp + limb_cnt, u->_mp_d, abs_usize, cnt);
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if (wlimb != 0)
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{
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wp[wsize] = wlimb;
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wsize++;
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}
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}
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else
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{
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MPN_COPY_DECR (wp + limb_cnt, u->_mp_d, abs_usize);
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}
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/* Zero all whole limbs at low end. Do it here and not before calling
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mpn_lshift, not to lose for U == W. */
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MPN_ZERO (wp, limb_cnt);
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w->_mp_size = usize >= 0 ? wsize : -wsize;
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}
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