1  /* mpfr_set_f -- set a MPFR number from a GNU MPF number
       2  
       3  Copyright 1999-2023 Free Software Foundation, Inc.
       4  Contributed by the AriC and Caramba 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  https://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  #define MPFR_NEED_MPF_INTERNALS
      25  #include "mpfr-impl.h"
      26  
      27  #ifndef MPFR_USE_MINI_GMP
      28  int
      29  mpfr_set_f (mpfr_ptr y, mpf_srcptr x, mpfr_rnd_t rnd_mode)
      30  {
      31    mp_limb_t *my, *mx, *tmp;
      32    int cnt;
      33    mp_size_t sx, sy;
      34    int inexact, carry = 0;
      35    MPFR_TMP_DECL(marker);
      36  
      37    sx = ABSIZ(x); /* number of limbs of the mantissa of x */
      38  
      39    if (sx == 0) /* x is zero */
      40      {
      41        MPFR_SET_ZERO(y);
      42        MPFR_SET_POS(y);
      43        return 0; /* 0 is exact */
      44      }
      45  
      46    if (SIZ(x) * MPFR_FROM_SIGN_TO_INT(MPFR_SIGN(y)) < 0)
      47      MPFR_CHANGE_SIGN (y);
      48  
      49    sy = MPFR_LIMB_SIZE (y);
      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        mpfr_prec_t xprec = (mpfr_prec_t) sx * GMP_NUMB_BITS;
      58  
      59        MPFR_TMP_MARK(marker);
      60        tmp = MPFR_TMP_LIMBS_ALLOC (sx);
      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) * GMP_NUMB_BITS may exceed the maximal exponent */
      85    if (EXP(x) > 1 + (__gmpfr_emax - 1) / GMP_NUMB_BITS)
      86      {
      87        /* EXP(x) >= 2 + floor((__gmpfr_emax-1)/GMP_NUMB_BITS)
      88           EXP(x) >= 2 + (__gmpfr_emax - GMP_NUMB_BITS) / GMP_NUMB_BITS
      89                  >= 1 + __gmpfr_emax / GMP_NUMB_BITS
      90           EXP(x) * GMP_NUMB_BITS >= __gmpfr_emax + GMP_NUMB_BITS
      91           Since 0 <= cnt <= GMP_NUMB_BITS-1, and 0 <= carry <= 1,
      92           we have then EXP(x) * GMP_NUMB_BITS - 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) * GMP_NUMB_BITS - cnt + carry;
      99      }
     100  
     101    return mpfr_check_range (y, inexact, rnd_mode);
     102  }
     103  #endif