gcc/mpfr/mul_ui.c

/* mpfr_mul_ui -- multiply a floating-point number by a machine integer
   mpfr_mul_si -- multiply a floating-point number by a machine integer

Copyright 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009 Free Software Foundation, Inc.
Contributed by the Arenaire and Cacao 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 2.1 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.LIB.  If not, write to
the Free Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston,
MA 02110-1301, USA. */

#define MPFR_NEED_LONGLONG_H
#include "mpfr-impl.h"

int
mpfr_mul_ui (mpfr_ptr y, mpfr_srcptr x, unsigned long int u, mp_rnd_t rnd_mode)
{
  mp_limb_t *yp;
  mp_size_t xn;
  int cnt, inexact;
  MPFR_TMP_DECL (marker);

  if (MPFR_UNLIKELY (MPFR_IS_SINGULAR (x)))
    {
      if (MPFR_IS_NAN (x))
        {
          MPFR_SET_NAN (y);
          MPFR_RET_NAN;
        }
      else if (MPFR_IS_INF (x))
        {
          if (u != 0)
            {
              MPFR_SET_INF (y);
              MPFR_SET_SAME_SIGN (y, x);
              MPFR_RET (0); /* infinity is exact */
            }
          else /* 0 * infinity */
            {
              MPFR_SET_NAN (y);
              MPFR_RET_NAN;
            }
        }
      else /* x is zero */
        {
          MPFR_ASSERTD (MPFR_IS_ZERO (x));
          MPFR_SET_ZERO (y);
          MPFR_SET_SAME_SIGN (y, x);
          MPFR_RET (0); /* zero is exact */
        }
    }
  else if (MPFR_UNLIKELY (u <= 1))
    {
      if (u < 1)
        {
          MPFR_SET_ZERO (y);
          MPFR_SET_SAME_SIGN (y, x);
          MPFR_RET (0); /* zero is exact */
        }
      else
        return mpfr_set (y, x, rnd_mode);
    }
  else if (MPFR_UNLIKELY (IS_POW2 (u)))
    return mpfr_mul_2si (y, x, MPFR_INT_CEIL_LOG2 (u), rnd_mode);

  yp = MPFR_MANT (y);
  xn = MPFR_LIMB_SIZE (x);

  MPFR_ASSERTD (xn < MP_SIZE_T_MAX);
  MPFR_TMP_MARK(marker);
  yp = (mp_ptr) MPFR_TMP_ALLOC ((size_t) (xn + 1) * BYTES_PER_MP_LIMB);

  MPFR_ASSERTN (u == (mp_limb_t) u);
  yp[xn] = mpn_mul_1 (yp, MPFR_MANT (x), xn, u);

  /* x * u is stored in yp[xn], ..., yp[0] */

  /* since the case u=1 was treated above, we have u >= 2, thus
     yp[xn] >= 1 since x was msb-normalized */
  MPFR_ASSERTD (yp[xn] != 0);
  if (MPFR_LIKELY (MPFR_LIMB_MSB (yp[xn]) == 0))
    {
      count_leading_zeros (cnt, yp[xn]);
      mpn_lshift (yp, yp, xn + 1, cnt);
    }
  else
    {
      cnt = 0;
    }

  /* now yp[xn], ..., yp[0] is msb-normalized too, and has at most
     PREC(x) + (BITS_PER_MP_LIMB - cnt) non-zero bits */
  MPFR_RNDRAW (inexact, y, yp, (mp_prec_t) (xn + 1) * BITS_PER_MP_LIMB,
               rnd_mode, MPFR_SIGN (x), cnt -- );

  MPFR_TMP_FREE (marker);

  cnt = BITS_PER_MP_LIMB - cnt;
  if (MPFR_UNLIKELY (__gmpfr_emax < MPFR_EMAX_MIN + cnt
                     || MPFR_GET_EXP (x) > __gmpfr_emax - cnt))
    return mpfr_overflow (y, rnd_mode, MPFR_SIGN(x));

  MPFR_SET_EXP (y, MPFR_GET_EXP (x) + cnt);
  MPFR_SET_SAME_SIGN (y, x);

  return inexact;
}

int mpfr_mul_si (mpfr_ptr y, mpfr_srcptr x, long int u, mp_rnd_t rnd_mode)
{
  int res;

  if (u >= 0)
    res = mpfr_mul_ui (y, x, u, rnd_mode);
  else
    {
      res = -mpfr_mul_ui (y, x, -u, MPFR_INVERT_RND (rnd_mode));
      MPFR_CHANGE_SIGN (y);
    }
  return res;
}