63 lines
1.9 KiB
C
63 lines
1.9 KiB
C
/* mpn_rshift -- Shift right low level.
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Copyright 1991, 1993, 1994, 1996, 2000, 2001, 2002 Free Software Foundation,
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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 Lesser General Public License as published by
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the Free Software Foundation; either version 2.1 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 Lesser General Public
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License for more details.
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You should have received a copy of the GNU Lesser 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., 51 Franklin Street, Fifth Floor, Boston,
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MA 02110-1301, 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 N limbs long) cnt bits to the right
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and store the n least significant limbs of the result at rp.
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The bits shifted out to the right are returned.
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Argument constraints:
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1. 0 < cnt < GMP_NUMB_BITS.
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2. If the result is to be written over the input, rp must be <= up.
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*/
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mp_limb_t
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mpn_rshift (mp_ptr rp, mp_srcptr up, mp_size_t n, unsigned int cnt)
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{
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mp_limb_t high_limb, low_limb;
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unsigned int tnc;
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mp_size_t i;
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mp_limb_t retval;
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ASSERT (n >= 1);
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ASSERT (cnt >= 1);
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ASSERT (cnt < GMP_NUMB_BITS);
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ASSERT (MPN_SAME_OR_INCR_P (rp, up, n));
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tnc = GMP_NUMB_BITS - cnt;
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high_limb = *up++;
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retval = (high_limb << tnc) & GMP_NUMB_MASK;
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low_limb = high_limb >> cnt;
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for (i = n - 1; i != 0; i--)
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{
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high_limb = *up++;
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*rp++ = low_limb | ((high_limb << tnc) & GMP_NUMB_MASK);
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low_limb = high_limb >> cnt;
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}
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*rp = low_limb;
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return retval;
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}
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