v3_1_6/src/sub_ui.c

/* mpfr_sub_ui -- subtract a floating-point number and a machine integer

Copyright 2000-2017 Free Software Foundation, Inc.
Contributed by the AriC and Caramba projects, INRIA.

This file is part of the GNU MPFR Library.

The GNU MPFR Library is free software; you can redistribute it and/or modify
it under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation; either version 3 of the License, or (at your
option) any later version.

The GNU MPFR Library is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
License for more details.

You should have received a copy of the GNU Lesser General Public License
along with the GNU MPFR Library; see the file COPYING.LESSER.  If not, see
http://www.gnu.org/licenses/ or write to the Free Software Foundation, Inc.,
51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA. */


#define MPFR_NEED_LONGLONG_H
#include "third_party/mpfr/v3_1_6/src/mpfr-impl.h"

int
mpfr_sub_ui (mpfr_ptr y, mpfr_srcptr x, unsigned long int u, mpfr_rnd_t rnd_mode)
{
  if (MPFR_LIKELY (u != 0))  /* if u=0, do nothing */
    {
      mpfr_t uu;
      mp_limb_t up[1];
      unsigned long cnt;
      int inex;

      MPFR_SAVE_EXPO_DECL (expo);

      MPFR_LOG_FUNC
        (("x[%Pu]=%.*Rg u=%lu rnd=%d",
          mpfr_get_prec(x), mpfr_log_prec, x, u, rnd_mode),
         ("y[%Pu]=%.*Rg inexact=%d",
          mpfr_get_prec(y), mpfr_log_prec, y, inex));

      MPFR_TMP_INIT1 (up, uu, GMP_NUMB_BITS);
      MPFR_ASSERTN (u == (mp_limb_t) u);
      count_leading_zeros (cnt, (mp_limb_t) u);
      *up = (mp_limb_t) u << cnt;

      /* Optimization note: Exponent save/restore operations may be
         removed if mpfr_sub works even when uu is out-of-range. */
      MPFR_SAVE_EXPO_MARK (expo);
      MPFR_SET_EXP (uu, GMP_NUMB_BITS - cnt);
      inex = mpfr_sub (y, x, uu, rnd_mode);
      MPFR_SAVE_EXPO_UPDATE_FLAGS (expo, __gmpfr_flags);
      MPFR_SAVE_EXPO_FREE (expo);
      return mpfr_check_range (y, inex, rnd_mode);
    }
  else
    return mpfr_set (y, x, rnd_mode);
}