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Annotation of OpenXM_contrib/gmp/mpq/md_2exp.c, Revision 1.1.1.1

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: }