91 lines
2.2 KiB
C
91 lines
2.2 KiB
C
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/* mpn_rshift -- Shift right a low-level natural-number integer.
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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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/* Shift U (pointed to by UP and USIZE limbs long) CNT bits to the right
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and store the USIZE least significant limbs of the result at WP.
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Return the size of the result.
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Argument constraints:
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0. U must be normalized (i.e. it's most significant limb != 0).
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1. 0 <= CNT < BITS_PER_MP_LIMB
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2. If the result is to be written over the input, WP must be <= UP.
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*/
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mp_size
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#ifdef __STDC__
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mpn_rshift (mp_ptr wp,
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mp_srcptr up, mp_size usize,
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unsigned cnt)
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#else
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mpn_rshift (wp, up, usize, cnt)
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mp_ptr wp;
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mp_srcptr up;
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mp_size usize;
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unsigned cnt;
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#endif
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{
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mp_limb high_limb, low_limb;
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unsigned sh_1, sh_2;
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mp_size i;
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if (usize == 0)
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return 0;
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sh_1 = cnt;
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if (sh_1 == 0)
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{
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if (wp != up)
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{
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/* Copy from low end to high end, to allow specified input/output
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overlapping. */
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for (i = 0; i < usize; i++)
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wp[i] = up[i];
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}
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return usize;
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}
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wp -= 1;
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sh_2 = BITS_PER_MP_LIMB - sh_1;
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high_limb = up[0];
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#if 0
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if (cy_limb != NULL)
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*cy_limb = high_limb << sh_2;
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#endif
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low_limb = high_limb;
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for (i = 1; i < usize; i++)
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{
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high_limb = up[i];
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wp[i] = (low_limb >> sh_1) | (high_limb << sh_2);
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low_limb = high_limb;
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}
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low_limb >>= sh_1;
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if (low_limb != 0)
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{
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wp[i] = low_limb;
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return usize;
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}
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return usize - 1;
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}
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