gcc/mpfr/cmp_ui.c

/* mpfr_cmp_ui_2exp -- compare a floating-point number with an unsigned
machine integer multiplied by a power of 2

Copyright 1999, 2001, 2002, 2003, 2004, 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"

/* returns a positive value if b > i*2^f,
           a negative value if b < i*2^f,
           zero if b = i*2^f.
   b must not be NaN
*/

int
mpfr_cmp_ui_2exp (mpfr_srcptr b, unsigned long int i, mp_exp_t f)
{
  if (MPFR_UNLIKELY( MPFR_IS_SINGULAR(b) ))
    {
      if (MPFR_IS_NAN (b))
        {
          MPFR_SET_ERANGE ();
          return 0;
        }
      else if (MPFR_IS_INF(b))
        return MPFR_INT_SIGN (b);
      else /* since b cannot be NaN, b=0 here */
        return i != 0 ? -1 : 0;
    }

  if (MPFR_IS_NEG (b))
    return -1;
  /* now b > 0 */
  else if (MPFR_UNLIKELY(i == 0))
    return 1;
  else /* b > 0, i > 0 */
    {
      mp_exp_t e;
      int k;
      mp_size_t bn;
      mp_limb_t c, *bp;

      /* i must be representable in a mp_limb_t */
      MPFR_ASSERTN(i == (mp_limb_t) i);

      e = MPFR_GET_EXP (b); /* 2^(e-1) <= b < 2^e */
      if (e <= f)
        return -1;
      if (f < MPFR_EMAX_MAX - BITS_PER_MP_LIMB &&
          e > f + BITS_PER_MP_LIMB)
        return 1;

      /* now f < e <= f + BITS_PER_MP_LIMB */
      c = (mp_limb_t) i;
      count_leading_zeros(k, c);
      if ((int) (e - f) > BITS_PER_MP_LIMB - k)
        return 1;
      if ((int) (e - f) < BITS_PER_MP_LIMB - k)
        return -1;

      /* now b and i*2^f have the same exponent */
      c <<= k;
      bn = (MPFR_PREC(b) - 1) / BITS_PER_MP_LIMB;
      bp = MPFR_MANT(b);
      if (bp[bn] > c)
        return 1;
      if (bp[bn] < c)
        return -1;

      /* most significant limbs agree, check remaining limbs from b */
      while (bn > 0)
        if (bp[--bn] != 0)
          return 1;
      return 0;
    }
}

#undef mpfr_cmp_ui
int
mpfr_cmp_ui (mpfr_srcptr b, unsigned long int i)
{
  return mpfr_cmp_ui_2exp (b, i, 0);
}