1  /* mpfr_ui_sub -- subtract a floating-point number from an integer
       2  
       3  Copyright 2000-2023 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  #include "mpfr-impl.h"
      25  
      26  int
      27  mpfr_ui_sub (mpfr_ptr y, unsigned long int u, mpfr_srcptr x, mpfr_rnd_t rnd_mode)
      28  {
      29    MPFR_LOG_FUNC
      30      (("u=%lu x[%Pd]=%.*Rg rnd=%d",
      31        u, mpfr_get_prec(x), mpfr_log_prec, x, rnd_mode),
      32       ("y[%Pd]=%.*Rg", mpfr_get_prec(y), mpfr_log_prec, y));
      33  
      34    /* (unsigned long) 0 is assumed to be a real 0 (unsigned) */
      35    if (MPFR_UNLIKELY (u == 0))
      36      return mpfr_neg (y, x, rnd_mode);
      37  
      38    if (MPFR_UNLIKELY (MPFR_IS_SINGULAR (x)))
      39      {
      40        if (MPFR_IS_NAN (x))
      41          {
      42            MPFR_SET_NAN (y);
      43            MPFR_RET_NAN;
      44          }
      45        if (MPFR_IS_INF (x))
      46          {
      47            /*  u - Inf = -Inf and u - -Inf = +Inf  */
      48            MPFR_SET_INF (y);
      49            MPFR_SET_OPPOSITE_SIGN (y, x);
      50            MPFR_RET (0); /* +/-infinity is exact */
      51          }
      52        MPFR_ASSERTD (MPFR_IS_ZERO (x) && u != 0);
      53        /* Note: the fact that u != 0 is important due to signed zeros. */
      54        /* u - 0 = u */
      55        return mpfr_set_ui (y, u, rnd_mode);
      56      }
      57  
      58    /* Main code */
      59    {
      60      int inex;
      61      MPFR_SAVE_EXPO_DECL (expo);
      62  
      63      /* Optimization note: Exponent save/restore operations may be
      64         removed if mpfr_sub works even when uu is out-of-range. */
      65      MPFR_SAVE_EXPO_MARK (expo);
      66  
      67  #ifdef MPFR_LONG_WITHIN_LIMB
      68      {
      69        mpfr_t uu;
      70        mp_limb_t up[1];
      71        int cnt;
      72  
      73        MPFR_TMP_INIT1 (up, uu, GMP_NUMB_BITS);
      74        /* So, u fits in a mp_limb_t, which justifies the casts below. */
      75        MPFR_ASSERTD (u != 0);
      76        count_leading_zeros (cnt, (mp_limb_t) u);
      77        up[0] = (mp_limb_t) u << cnt;
      78        MPFR_SET_EXP (uu, GMP_NUMB_BITS - cnt);
      79        inex = mpfr_sub (y, uu, x, rnd_mode);
      80      }
      81  #else
      82      {
      83        mpfr_t uu;
      84  
      85        mpfr_init2 (uu, sizeof (unsigned long) * CHAR_BIT);
      86        mpfr_set_ui (uu, u, MPFR_RNDZ);
      87        inex = mpfr_sub (y, uu, x, rnd_mode);
      88        mpfr_clear (uu);
      89      }
      90  #endif
      91  
      92      MPFR_SAVE_EXPO_UPDATE_FLAGS (expo, __gmpfr_flags);
      93      MPFR_SAVE_EXPO_FREE (expo);
      94      return mpfr_check_range (y, inex, rnd_mode);
      95    }
      96  }