lshiftc.c
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上传日期:2022-08-06
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- /* mpn_lshiftc -- Shift left low level with complement.
- Copyright 1991, 1993, 1994, 1996, 2000, 2001, 2002, 2009 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 Lesser General Public License as published by
- the Free Software Foundation; either version 3 of the License, 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 Lesser General Public
- License for more details.
- You should have received a copy of the GNU Lesser General Public License
- along with the GNU MP Library. If not, see http://www.gnu.org/licenses/. */
- #include "gmp.h"
- #include "gmp-impl.h"
- /* Shift U (pointed to by up and n limbs long) cnt bits to the left
- and store the n least significant limbs of the result at rp.
- Return the bits shifted out from the most significant limb.
- Argument constraints:
- 1. 0 < cnt < GMP_NUMB_BITS.
- 2. If the result is to be written over the input, rp must be >= up.
- */
- mp_limb_t
- mpn_lshiftc (mp_ptr rp, mp_srcptr up, mp_size_t n, unsigned int cnt)
- {
- mp_limb_t high_limb, low_limb;
- unsigned int tnc;
- mp_size_t i;
- mp_limb_t retval;
- ASSERT (n >= 1);
- ASSERT (cnt >= 1);
- ASSERT (cnt < GMP_NUMB_BITS);
- ASSERT (MPN_SAME_OR_DECR_P (rp, up, n));
- up += n;
- rp += n;
- tnc = GMP_NUMB_BITS - cnt;
- low_limb = *--up;
- retval = low_limb >> tnc;
- high_limb = (low_limb << cnt);
- for (i = n - 1; i != 0; i--)
- {
- low_limb = *--up;
- *--rp = (~(high_limb | (low_limb >> tnc))) & GMP_NUMB_MASK;
- high_limb = low_limb << cnt;
- }
- *--rp = (~high_limb) & GMP_NUMB_MASK;
- return retval;
- }