contrib/mpfr/set_f.c

   1 /* mpfr_set_f -- set a MPFR number from a GNU MPF number
   2
   3 Copyright 1999, 2000, 2001, 2002, 2003, 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 int
  27 mpfr_set_f (mpfr_ptr y, mpf_srcptr x, mp_rnd_t rnd_mode)
  28 {
  29   mp_limb_t *my, *mx, *tmp;
  30   unsigned long cnt, sx, sy;
  31   int inexact, carry = 0;
  32   MPFR_TMP_DECL(marker);
  33
  34   sx = ABS(SIZ(x)); /* number of limbs of the mantissa of x */
  35
  36   if (sx == 0) /* x is zero */
  37     {
  38       MPFR_CLEAR_FLAGS (y);
  39       MPFR_SET_ZERO(y);
  40       MPFR_SET_POS(y);
  41       return 0; /* 0 is exact */
  42     }
  43
  44   if (SIZ(x) * MPFR_FROM_SIGN_TO_INT(MPFR_SIGN(y)) < 0)
  45     MPFR_CHANGE_SIGN (y);
  46
  47   MPFR_CLEAR_FLAGS (y);
  48
  49   sy = 1 + (MPFR_PREC(y) - 1) / BITS_PER_MP_LIMB;
  50   my = MPFR_MANT(y);
  51   mx = PTR(x);
  52
  53   count_leading_zeros(cnt, mx[sx - 1]);
  54
  55   if (sy <= sx) /* we may have to round even when sy = sx */
  56     {
  57       unsigned long xprec = sx * BITS_PER_MP_LIMB;
  58
  59       MPFR_TMP_MARK(marker);
  60       tmp = (mp_limb_t*) MPFR_TMP_ALLOC(sx * BYTES_PER_MP_LIMB);
  61       if (cnt)
  62         mpn_lshift (tmp, mx, sx, cnt);
  63       else
  64         /* FIXME: we may avoid the copy here, and directly call mpfr_round_raw
  65            on mx instead of tmp */
  66         MPN_COPY (tmp, mx, sx);
  67       carry = mpfr_round_raw (my, tmp, xprec, (SIZ(x) < 0), MPFR_PREC(y),
  68                               rnd_mode, &inexact);
  69       if (MPFR_UNLIKELY(carry)) /* result is a power of two */
  70         my[sy - 1] = MPFR_LIMB_HIGHBIT;
  71       MPFR_TMP_FREE(marker);
  72     }
  73   else
  74     {
  75       if (cnt)
  76         mpn_lshift (my + sy - sx, mx, sx, cnt);
  77       else
  78         MPN_COPY (my + sy - sx, mx, sx);
  79       MPN_ZERO(my, sy - sx);
  80       /* no rounding necessary, since y has a larger mantissa */
  81       inexact = 0;
  82     }
  83
  84   /* warning: EXP(x) * BITS_PER_MP_LIMB may exceed the maximal exponent */
  85   if (EXP(x) > 1 + (__gmpfr_emax - 1) / BITS_PER_MP_LIMB)
  86     {
  87       /* EXP(x) >= 2 + floor((__gmpfr_emax-1)/BITS_PER_MP_LIMB)
  88          EXP(x) >= 2 + (__gmpfr_emax - BITS_PER_MP_LIMB) / BITS_PER_MP_LIMB
  89                 >= 1 + __gmpfr_emax / BITS_PER_MP_LIMB
  90          EXP(x) * BITS_PER_MP_LIMB >= __gmpfr_emax + BITS_PER_MP_LIMB
  91          Since 0 <= cnt <= BITS_PER_MP_LIMB-1, and 0 <= carry <= 1,
  92          we have then EXP(x) * BITS_PER_MP_LIMB - cnt + carry > __gmpfr_emax */
  93       return mpfr_overflow (y, rnd_mode, MPFR_SIGN (y));
  94     }
  95   else
  96     {
  97       /* Do not use MPFR_SET_EXP as the exponent may be out of range. */
  98       MPFR_EXP (y) = EXP (x) * BITS_PER_MP_LIMB - (mp_exp_t) cnt + carry;
  99     }
 100
 101   return mpfr_check_range (y, inexact, rnd_mode);
 102 }