contrib/mpfr/set_q.c

   1 /* mpfr_set_q -- set a floating-point number from a multiple-precision rational
   2
   3 Copyright 2000, 2001, 2002, 2004, 2005, 2006, 2007, 2008, 2009 Free Software Foundation, Inc.
   4 Contributed by the Arenaire and Cacao projects, INRIA.
   5
   6 This file is part of the GNU MPFR Library.
   7
   8 The GNU MPFR 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 MPFR 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 MPFR Library; see the file COPYING.LIB.  If not, write to
  20 the Free Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston,
  21 MA 02110-1301, USA. */
  22
  23 #define MPFR_NEED_LONGLONG_H
  24 #include "mpfr-impl.h"
  25
  26 /*
  27  * Set f to z, choosing the smallest precision for f
  28  * so that z = f*(2^BPML)*zs*2^(RetVal)
  29  */
  30 static int
  31 set_z (mpfr_ptr f, mpz_srcptr z, mp_size_t *zs)
  32 {
  33   mp_limb_t *p;
  34   mp_size_t s;
  35   int c;
  36   mp_prec_t pf;
  37
  38   MPFR_ASSERTD (mpz_sgn (z) != 0);
  39
  40   /* Remove useless ending 0 */
  41   for (p = PTR (z), s = *zs = ABS (SIZ (z)) ; *p == 0; p++, s--)
  42     MPFR_ASSERTD (s >= 0);
  43
  44   /* Get working precision */
  45   count_leading_zeros (c, p[s-1]);
  46   pf = s * BITS_PER_MP_LIMB - c;
  47   if (pf < MPFR_PREC_MIN)
  48     pf = MPFR_PREC_MIN;
  49   mpfr_init2 (f, pf);
  50
  51   /* Copy Mantissa */
  52   if (MPFR_LIKELY (c))
  53     mpn_lshift (MPFR_MANT (f), p, s, c);
  54   else
  55     MPN_COPY (MPFR_MANT (f), p, s);
  56
  57   MPFR_SET_SIGN (f, mpz_sgn (z));
  58   MPFR_SET_EXP (f, 0);
  59
  60   return -c;
  61 }
  62
  63 /* set f to the rational q */
  64 int
  65 mpfr_set_q (mpfr_ptr f, mpq_srcptr q, mp_rnd_t rnd)
  66 {
  67   mpz_srcptr num, den;
  68   mpfr_t n, d;
  69   int inexact;
  70   int cn, cd;
  71   long shift;
  72   mp_size_t sn, sd;
  73   MPFR_SAVE_EXPO_DECL (expo);
  74
  75   num = mpq_numref (q);
  76   den = mpq_denref (q);
  77   /* NAN and INF for mpq are not really documented, but could be found */
  78   if (MPFR_UNLIKELY (mpz_sgn (num) == 0))
  79     {
  80       if (MPFR_UNLIKELY (mpz_sgn (den) == 0))
  81         {
  82           MPFR_SET_NAN (f);
  83           MPFR_RET_NAN;
  84         }
  85       else
  86         {
  87           MPFR_SET_ZERO (f);
  88           MPFR_SET_POS (f);
  89           MPFR_RET (0);
  90         }
  91     }
  92   if (MPFR_UNLIKELY (mpz_sgn (den) == 0))
  93     {
  94       MPFR_SET_INF (f);
  95       MPFR_SET_SIGN (f, mpz_sgn (num));
  96       MPFR_RET (0);
  97     }
  98
  99   MPFR_SAVE_EXPO_MARK (expo);
 100
 101   cn = set_z (n, num, &sn);
 102   cd = set_z (d, den, &sd);
 103
 104   sn -= sd;
 105   if (MPFR_UNLIKELY (sn > MPFR_EMAX_MAX / BITS_PER_MP_LIMB))
 106     {
 107       inexact = mpfr_overflow (f, rnd, MPFR_SIGN (f));
 108       goto end;
 109     }
 110   if (MPFR_UNLIKELY (sn < MPFR_EMIN_MIN / BITS_PER_MP_LIMB -1))
 111     {
 112       if (rnd == GMP_RNDN)
 113         rnd = GMP_RNDZ;
 114       inexact = mpfr_underflow (f, rnd, MPFR_SIGN (f));
 115       goto end;
 116     }
 117
 118   inexact = mpfr_div (f, n, d, rnd);
 119   shift = BITS_PER_MP_LIMB*sn+cn-cd;
 120   MPFR_ASSERTD (shift == BITS_PER_MP_LIMB*sn+cn-cd);
 121   cd = mpfr_mul_2si (f, f, shift, rnd);
 122   MPFR_SAVE_EXPO_FREE (expo);
 123   if (MPFR_UNLIKELY (cd != 0))
 124     inexact = cd;
 125   else
 126     inexact = mpfr_check_range (f, inexact, rnd);
 127  end:
 128   mpfr_clear (d);
 129   mpfr_clear (n);
 130   return inexact;
 131 }
 132
 133