94 lines
2.4 KiB
C
94 lines
2.4 KiB
C
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/* mpz_com(mpz_ptr dst, mpz_ptr src) -- Assign the bit-complemented value of
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SRC to DST.
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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_com (mpz_ptr dst, mpz_srcptr src)
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#else
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mpz_com (dst, src)
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mpz_ptr dst;
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mpz_srcptr src;
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#endif
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{
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mp_size_t size = src->_mp_size;
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mp_srcptr src_ptr;
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mp_ptr dst_ptr;
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if (size >= 0)
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{
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/* As with infinite precision: one's complement, two's complement.
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But this can be simplified using the identity -x = ~x + 1.
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So we're going to compute (~~x) + 1 = x + 1! */
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if (dst->_mp_alloc < size + 1)
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_mpz_realloc (dst, size + 1);
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src_ptr = src->_mp_d;
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dst_ptr = dst->_mp_d;
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if (size == 0)
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{
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/* Special case, as mpn_add wants the first arg's size >= the
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second arg's size. */
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dst_ptr[0] = 1;
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dst->_mp_size = -1;
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return;
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}
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{
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mp_limb_t cy;
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cy = mpn_add_1 (dst_ptr, src_ptr, size, (mp_limb_t) 1);
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if (cy)
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{
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dst_ptr[size] = cy;
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size++;
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}
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}
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/* Store a negative size, to indicate ones-extension. */
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dst->_mp_size = -size;
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}
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else
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{
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/* As with infinite precision: two's complement, then one's complement.
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But that can be simplified using the identity -x = ~(x - 1).
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So we're going to compute ~~(x - 1) = x - 1! */
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size = -size;
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if (dst->_mp_alloc < size)
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_mpz_realloc (dst, size);
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src_ptr = src->_mp_d;
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dst_ptr = dst->_mp_d;
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mpn_sub_1 (dst_ptr, src_ptr, size, (mp_limb_t) 1);
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size -= dst_ptr[size - 1] == 0;
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/* Store a positive size, to indicate zero-extension. */
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dst->_mp_size = size;
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}
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}
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