97 lines
2.3 KiB
C
97 lines
2.3 KiB
C
/* mpz_com(MP_INT *dst, MP_INT *src) -- Assign the bit-complemented value of
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SRC to DST.
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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_com (MP_INT *dst, const MP_INT *src)
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#else
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mpz_com (dst, src)
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MP_INT *dst;
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const MP_INT *src;
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#endif
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{
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mp_size size = src->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->alloc < size + 1)
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_mpz_realloc (dst, size + 1);
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src_ptr = src->d;
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dst_ptr = dst->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->size = -1;
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return;
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}
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{
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mp_limb one = 1;
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int cy;
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cy = mpn_add (dst_ptr, src_ptr, size, &one, 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->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->alloc < size)
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_mpz_realloc (dst, size);
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src_ptr = src->d;
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dst_ptr = dst->d;
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{
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mp_limb one = 1;
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size += mpn_sub (dst_ptr, src_ptr, size, &one, 1);
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}
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/* Store a positive size, to indicate zero-extension. */
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dst->size = size;
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}
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}
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