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Diffstat (limited to 'gnu/lib/libgmp/mpz_com.c')
-rw-r--r-- | gnu/lib/libgmp/mpz_com.c | 96 |
1 files changed, 96 insertions, 0 deletions
diff --git a/gnu/lib/libgmp/mpz_com.c b/gnu/lib/libgmp/mpz_com.c new file mode 100644 index 0000000..3c0d3b1 --- /dev/null +++ b/gnu/lib/libgmp/mpz_com.c @@ -0,0 +1,96 @@ +/* mpz_com(MP_INT *dst, MP_INT *src) -- Assign the bit-complemented value of + SRC to DST. + +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_com (MP_INT *dst, const MP_INT *src) +#else +mpz_com (dst, src) + MP_INT *dst; + const MP_INT *src; +#endif +{ + mp_size size = src->size; + mp_srcptr src_ptr; + mp_ptr dst_ptr; + + if (size >= 0) + { + /* As with infinite precision: one's complement, two's complement. + But this can be simplified using the identity -x = ~x + 1. + So we're going to compute (~~x) + 1 = x + 1! */ + + if (dst->alloc < size + 1) + _mpz_realloc (dst, size + 1); + + src_ptr = src->d; + dst_ptr = dst->d; + + if (size == 0) + { + /* Special case, as mpn_add wants the first arg's size >= the + second arg's size. */ + dst_ptr[0] = 1; + dst->size = -1; + return; + } + + { + mp_limb one = 1; + int cy; + + cy = mpn_add (dst_ptr, src_ptr, size, &one, 1); + if (cy) + { + dst_ptr[size] = cy; + size++; + } + } + + /* Store a negative size, to indicate ones-extension. */ + dst->size = -size; + } + else + { + /* As with infinite precision: two's complement, then one's complement. + But that can be simplified using the identity -x = ~(x - 1). + So we're going to compute ~~(x - 1) = x - 1! */ + size = -size; + + if (dst->alloc < size) + _mpz_realloc (dst, size); + + src_ptr = src->d; + dst_ptr = dst->d; + + { + mp_limb one = 1; + + size += mpn_sub (dst_ptr, src_ptr, size, &one, 1); + } + + /* Store a positive size, to indicate zero-extension. */ + dst->size = size; + } +} |