1  /* mpfr_fits_*_p -- test whether an mpfr fits a C signed type.
       2  
       3  Copyright 2003-2023 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  #include "mpfr-impl.h"
      24  
      25  /* The original version of this file came from GMP's mpf/fits_s.h;
      26     it has been adapted for MPFR.  In particular, the result can be
      27     rounded away from zero. */
      28  
      29  int
      30  FUNCTION (mpfr_srcptr f, mpfr_rnd_t rnd)
      31  {
      32    mpfr_flags_t saved_flags;
      33    mpfr_exp_t e;
      34    int prec;
      35    mpfr_t x;
      36    int neg;
      37    int res;
      38  
      39    if (MPFR_UNLIKELY (MPFR_IS_SINGULAR (f)))
      40      /* Zero always fit */
      41      return MPFR_IS_ZERO (f) ? 1 : 0;
      42  
      43    /* now it fits if either
      44       (a) MINIMUM <= f <= MAXIMUM
      45       (b) or MINIMUM <= round(f, prec(slong), rnd) <= MAXIMUM */
      46  
      47    e = MPFR_GET_EXP (f);
      48    if (e < 1)
      49      return 1; /* |f| < 1: always fits */
      50  
      51    neg = MPFR_IS_NEG (f);
      52  
      53    /* let EXTREMUM be MAXIMUM if f > 0, and MINIMUM if f < 0 */
      54  
      55    /* first compute prec(EXTREMUM), this could be done at configure time,
      56       but the result can depend on neg (the loop is moved inside the "if"
      57       to give the compiler a better chance to compute prec statically) */
      58    if (neg)
      59      {
      60        unsigned TYPE s;
      61        /* In C90, the division on negative integers isn't well-defined. */
      62        s = SAFE_ABS (unsigned TYPE, MINIMUM);
      63        for (prec = 0; s != 0; s /= 2, prec ++);
      64      }
      65    else
      66      {
      67        TYPE s;
      68        s = MAXIMUM;
      69        for (prec = 0; s != 0; s /= 2, prec ++);
      70      }
      71  
      72    /* EXTREMUM needs prec bits, i.e. 2^(prec-1) <= |EXTREMUM| < 2^prec */
      73  
      74     /* if e <= prec - 1, then f < 2^(prec-1) <= |EXTREMUM| */
      75    if (e <= prec - 1)
      76      return 1;
      77  
      78    /* if e >= prec + 1, then f >= 2^prec > |EXTREMUM| */
      79    if (e >= prec + 1)
      80      return 0;
      81  
      82    MPFR_ASSERTD (e == prec);
      83  
      84    /* hard case: first round to prec bits, then check */
      85    saved_flags = __gmpfr_flags;
      86    mpfr_init2 (x, prec);
      87    /* for RNDF, it suffices to check it fits when rounded away from zero */
      88    mpfr_set (x, f, (rnd == MPFR_RNDF) ? MPFR_RNDA : rnd);
      89    /* Warning! Due to the rounding, x can be an infinity. Here we use
      90       the fact that singular numbers have a special exponent field,
      91       thus well-defined and different from e, in which case this means
      92       that the number does not fit. That's why we use MPFR_EXP, not
      93       MPFR_GET_EXP. */
      94    res = neg ? (mpfr_cmp_si (x, MINIMUM) >= 0) : (MPFR_EXP (x) == e);
      95    mpfr_clear (x);
      96    __gmpfr_flags = saved_flags;
      97    return res;
      98  }