1  /* mpfr_fits_intmax_p -- test whether an mpfr fits an intmax_t.
       2  
       3  Copyright 2004, 2006-2023 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_INTMAX_H
      24  #include "mpfr-impl.h"
      25  
      26  #ifdef _MPFR_H_HAVE_INTMAX_T
      27  
      28  /* We can't use fits_s.h as it uses mpfr_cmp_si */
      29  int
      30  mpfr_fits_intmax_p (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, y;
      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_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        uintmax_t s;
      61        /* In C90, the division on negative integers isn't well-defined. */
      62        s = SAFE_ABS (uintmax_t, INTMAX_MIN);
      63        for (prec = 0; s != 0; s /= 2, prec ++);
      64      }
      65    else
      66      {
      67        intmax_t s;
      68        s = INTMAX_MAX;
      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 is necessary and sufficient to check it fits when rounding
      88       away from zero */
      89    mpfr_set (x, f, (rnd == MPFR_RNDF) ? MPFR_RNDA : rnd);
      90  
      91    if (neg)
      92      {
      93        mpfr_init2 (y, prec);
      94        mpfr_set_sj (y, INTMAX_MIN, MPFR_RNDN);
      95        res = mpfr_cmp (x, y) >= 0;
      96        mpfr_clear (y);
      97      }
      98    else
      99      {
     100        /* Warning! Due to the rounding, x can be an infinity. Here we use
     101           the fact that singular numbers have a special exponent field,
     102           thus well-defined and different from e, in which case this means
     103           that the number does not fit. That's why we use MPFR_EXP, not
     104           MPFR_GET_EXP. */
     105        res = MPFR_EXP (x) == e;
     106      }
     107  
     108    mpfr_clear (x);
     109    __gmpfr_flags = saved_flags;
     110    return res;
     111  }
     112  
     113  #endif