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Annotation of OpenXM_contrib/gmp/mpq/md_2exp.c, Revision 1.1

1.1     ! ohara       1: /* mpq_mul_2exp, mpq_div_2exp - multiply or divide by 2^N */
        !             2:
        !             3: /*
        !             4: Copyright 2000, 2002 Free Software Foundation, Inc.
        !             5:
        !             6: This file is part of the GNU MP Library.
        !             7:
        !             8: The GNU MP Library is free software; you can redistribute it and/or modify
        !             9: it under the terms of the GNU Lesser General Public License as published by
        !            10: the Free Software Foundation; either version 2.1 of the License, or (at your
        !            11: option) any later version.
        !            12:
        !            13: The GNU MP Library is distributed in the hope that it will be useful, but
        !            14: WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
        !            15: or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
        !            16: License for more details.
        !            17:
        !            18: You should have received a copy of the GNU Lesser General Public License
        !            19: along with the GNU MP Library; see the file COPYING.LIB.  If not, write to
        !            20: the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
        !            21: MA 02111-1307, USA.
        !            22: */
        !            23:
        !            24: #include "gmp.h"
        !            25: #include "gmp-impl.h"
        !            26: #include "longlong.h"
        !            27:
        !            28:
        !            29: /* The multiplier/divisor "n", representing 2^n, is applied by right shifting
        !            30:    "r" until it's odd (if it isn't already), and left shifting "l" for the
        !            31:    rest. */
        !            32:
        !            33: static void
        !            34: mord_2exp (mpz_ptr ldst, mpz_ptr rdst, mpz_srcptr lsrc, mpz_srcptr rsrc,
        !            35:            unsigned long n)
        !            36: {
        !            37:   mp_size_t  rsrc_size = SIZ(rsrc);
        !            38:   mp_size_t  len = ABS (rsrc_size);
        !            39:   mp_ptr     rsrc_ptr = PTR(rsrc);
        !            40:   mp_ptr     p, rdst_ptr;
        !            41:   mp_limb_t  plow;
        !            42:
        !            43:   p = rsrc_ptr;
        !            44:   plow = *p;
        !            45:   while (n >= GMP_NUMB_BITS && plow == 0)
        !            46:     {
        !            47:       n -= GMP_NUMB_BITS;
        !            48:       p++;
        !            49:       plow = *p;
        !            50:     }
        !            51:
        !            52:   /* no realloc here if rsrc==rdst, so p and rsrc_ptr remain valid */
        !            53:   len -= (p - rsrc_ptr);
        !            54:   MPZ_REALLOC (rdst, len);
        !            55:   rdst_ptr = PTR(rdst);
        !            56:
        !            57:   if ((plow & 1) || n == 0)
        !            58:     {
        !            59:       /* need DECR when src==dst */
        !            60:       if (p != rdst_ptr)
        !            61:         MPN_COPY_DECR (rdst_ptr, p, len);
        !            62:     }
        !            63:   else
        !            64:     {
        !            65:       unsigned long  shift;
        !            66:       if (plow == 0)
        !            67:         shift = n;
        !            68:       else
        !            69:         {
        !            70:           count_trailing_zeros (shift, plow);
        !            71:           shift = MIN (shift, n);
        !            72:         }
        !            73:       mpn_rshift (rdst_ptr, p, len, shift);
        !            74:       len -= (rdst_ptr[len-1] == 0);
        !            75:       n -= shift;
        !            76:     }
        !            77:   SIZ(rdst) = (rsrc_size >= 0) ? len : -len;
        !            78:
        !            79:   if (n)
        !            80:     mpz_mul_2exp (ldst, lsrc, n);
        !            81:   else if (ldst != lsrc)
        !            82:     mpz_set (ldst, lsrc);
        !            83: }
        !            84:
        !            85:
        !            86: void
        !            87: mpq_mul_2exp (mpq_ptr dst, mpq_srcptr src, unsigned long n)
        !            88: {
        !            89:   mord_2exp (mpq_numref (dst), mpq_denref (dst),
        !            90:              mpq_numref (src), mpq_denref (src), n);
        !            91: }
        !            92:
        !            93: void
        !            94: mpq_div_2exp (mpq_ptr dst, mpq_srcptr src, unsigned long n)
        !            95: {
        !            96:   if (SIZ (mpq_numref(src)) == 0)
        !            97:     {
        !            98:       dst->_mp_num._mp_size = 0;
        !            99:       dst->_mp_den._mp_size = 1;
        !           100:       dst->_mp_den._mp_d[0] = 1;
        !           101:       return;
        !           102:     }
        !           103:
        !           104:   mord_2exp (mpq_denref (dst), mpq_numref (dst),
        !           105:              mpq_denref (src), mpq_numref (src), n);
        !           106: }