107 lines
2.8 KiB
C
107 lines
2.8 KiB
C
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/* mpq_mul_2exp, mpq_div_2exp - multiply or divide by 2^N */
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/*
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Copyright 2000, 2002 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 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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*/
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#include "gmp.h"
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#include "gmp-impl.h"
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#include "longlong.h"
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/* The multiplier/divisor "n", representing 2^n, is applied by right shifting
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"r" until it's odd (if it isn't already), and left shifting "l" for the
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rest. */
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static void
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mord_2exp (mpz_ptr ldst, mpz_ptr rdst, mpz_srcptr lsrc, mpz_srcptr rsrc,
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unsigned long n)
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{
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mp_size_t rsrc_size = SIZ(rsrc);
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mp_size_t len = ABS (rsrc_size);
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mp_ptr rsrc_ptr = PTR(rsrc);
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mp_ptr p, rdst_ptr;
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mp_limb_t plow;
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p = rsrc_ptr;
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plow = *p;
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while (n >= GMP_NUMB_BITS && plow == 0)
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{
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n -= GMP_NUMB_BITS;
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p++;
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plow = *p;
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}
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/* no realloc here if rsrc==rdst, so p and rsrc_ptr remain valid */
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len -= (p - rsrc_ptr);
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MPZ_REALLOC (rdst, len);
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rdst_ptr = PTR(rdst);
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if ((plow & 1) || n == 0)
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{
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/* need DECR when src==dst */
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if (p != rdst_ptr)
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MPN_COPY_DECR (rdst_ptr, p, len);
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}
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else
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{
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unsigned long shift;
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if (plow == 0)
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shift = n;
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else
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{
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count_trailing_zeros (shift, plow);
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shift = MIN (shift, n);
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}
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mpn_rshift (rdst_ptr, p, len, shift);
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len -= (rdst_ptr[len-1] == 0);
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n -= shift;
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}
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SIZ(rdst) = (rsrc_size >= 0) ? len : -len;
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if (n)
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mpz_mul_2exp (ldst, lsrc, n);
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else if (ldst != lsrc)
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mpz_set (ldst, lsrc);
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}
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void
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mpq_mul_2exp (mpq_ptr dst, mpq_srcptr src, unsigned long n)
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{
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mord_2exp (mpq_numref (dst), mpq_denref (dst),
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mpq_numref (src), mpq_denref (src), n);
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}
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void
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mpq_div_2exp (mpq_ptr dst, mpq_srcptr src, unsigned long n)
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{
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if (SIZ (mpq_numref(src)) == 0)
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{
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dst->_mp_num._mp_size = 0;
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dst->_mp_den._mp_size = 1;
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dst->_mp_den._mp_d[0] = 1;
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return;
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}
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mord_2exp (mpq_denref (dst), mpq_numref (dst),
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mpq_denref (src), mpq_numref (src), n);
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}
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