69 lines
1.7 KiB
C
69 lines
1.7 KiB
C
/* mpz_mul_2exp -- Multiply a bignum by 2**CNT
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Copyright (C) 1991 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 General Public License as published by
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the Free Software Foundation; either version 2, or (at your option)
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any later version.
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The GNU MP Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with the GNU MP Library; see the file COPYING. If not, write to
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the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, 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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#ifdef __STDC__
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mpz_mul_2exp (MP_INT *w, const MP_INT *u, unsigned long int cnt)
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#else
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mpz_mul_2exp (w, u, cnt)
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MP_INT *w;
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const MP_INT *u;
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unsigned long int cnt;
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#endif
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{
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mp_size usize = u->size;
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mp_size abs_usize = ABS (usize);
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mp_size wsize;
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mp_size limb_cnt;
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mp_ptr wp;
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mp_limb wdigit;
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if (usize == 0)
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{
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w->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->alloc < wsize)
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_mpz_realloc (w, wsize);
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wp = w->d;
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wdigit = mpn_lshift (wp + limb_cnt, u->d, abs_usize,
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cnt % BITS_PER_MP_LIMB);
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wsize = abs_usize + limb_cnt;
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if (wdigit != 0)
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{
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wp[wsize] = wdigit;
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wsize++;
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}
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/* Zero all whole digits at low end. Do it here and not before calling
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mpn_lshift, not to loose for U == W. */
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MPN_ZERO (wp, limb_cnt);
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w->size = (usize >= 0) ? wsize : -wsize;
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}
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