source/libs/mpfr/mpfr-3.1.3/src/set_q.c

   1 /* mpfr_set_q -- set a floating-point number from a multiple-precision rational
   2
   3 Copyright 2000-2002, 2004-2015 Free Software Foundation, Inc.
   4 Contributed by the AriC and Caramel 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 3 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.LESSER.  If not, see
  20 http://www.gnu.org/licenses/ or write to the Free Software Foundation, Inc.,
  21 51 Franklin St, Fifth Floor, Boston, 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   mpfr_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 * GMP_NUMB_BITS - 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, mpfr_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 / GMP_NUMB_BITS))
 106     {
 107       MPFR_SAVE_EXPO_FREE (expo);
 108       inexact = mpfr_overflow (f, rnd, MPFR_SIGN (f));
 109       goto end;
 110     }
 111   if (MPFR_UNLIKELY (sn < MPFR_EMIN_MIN / GMP_NUMB_BITS -1))
 112     {
 113       MPFR_SAVE_EXPO_FREE (expo);
 114       if (rnd == MPFR_RNDN)
 115         rnd = MPFR_RNDZ;
 116       inexact = mpfr_underflow (f, rnd, MPFR_SIGN (f));
 117       goto end;
 118     }
 119
 120   inexact = mpfr_div (f, n, d, rnd);
 121   shift = GMP_NUMB_BITS*sn+cn-cd;
 122   MPFR_ASSERTD (shift == GMP_NUMB_BITS*sn+cn-cd);
 123   cd = mpfr_mul_2si (f, f, shift, rnd);
 124   MPFR_SAVE_EXPO_FREE (expo);
 125   if (MPFR_UNLIKELY (cd != 0))
 126     inexact = cd;
 127   else
 128     inexact = mpfr_check_range (f, inexact, rnd);
 129  end:
 130   mpfr_clear (d);
 131   mpfr_clear (n);
 132   MPFR_RET (inexact);
 133 }
 134
 135