contrib/mpfr/cmp_si.c

   1 /* mpfr_cmp_si_2exp -- compare a floating-point number with a signed
   2 machine integer multiplied by a power of 2
   3
   4 Copyright 1999, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009 Free Software Foundation, Inc.
   5 Contributed by the Arenaire and Cacao projects, INRIA.
   6
   7 This file is part of the GNU MPFR Library.
   8
   9 The GNU MPFR Library is free software; you can redistribute it and/or modify
  10 it under the terms of the GNU Lesser General Public License as published by
  11 the Free Software Foundation; either version 2.1 of the License, or (at your
  12 option) any later version.
  13
  14 The GNU MPFR Library is distributed in the hope that it will be useful, but
  15 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
  16 or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
  17 License for more details.
  18
  19 You should have received a copy of the GNU Lesser General Public License
  20 along with the GNU MPFR Library; see the file COPYING.LIB.  If not, write to
  21 the Free Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston,
  22 MA 02110-1301, USA. */
  23
  24 #define MPFR_NEED_LONGLONG_H
  25 #include "mpfr-impl.h"
  26
  27 /* returns a positive value if b > i*2^f,
  28            a negative value if b < i*2^f,
  29            zero if b = i*2^f.
  30    b must not be NaN.
  31 */
  32
  33 int
  34 mpfr_cmp_si_2exp (mpfr_srcptr b, long int i, mp_exp_t f)
  35 {
  36   int si;
  37
  38   si = i < 0 ? -1 : 1; /* sign of i */
  39   if (MPFR_UNLIKELY (MPFR_IS_SINGULAR (b)))
  40     {
  41       if (MPFR_IS_INF(b))
  42         return MPFR_INT_SIGN(b);
  43       else if (MPFR_IS_ZERO(b))
  44         return i != 0 ? -si : 0;
  45       /* NAN */
  46       MPFR_SET_ERANGE ();
  47       return 0;
  48     }
  49   else if (MPFR_SIGN(b) != si || i == 0)
  50     return MPFR_INT_SIGN (b);
  51   else /* b and i are of same sign si */
  52     {
  53       mp_exp_t e;
  54       unsigned long ai;
  55       int k;
  56       mp_size_t bn;
  57       mp_limb_t c, *bp;
  58
  59       ai = SAFE_ABS(unsigned long, i);
  60
  61       /* ai must be representable in a mp_limb_t */
  62       MPFR_ASSERTN(ai == (mp_limb_t) ai);
  63
  64       e = MPFR_GET_EXP (b); /* 2^(e-1) <= b < 2^e */
  65       if (e <= f)
  66         return -si;
  67       if (f < MPFR_EMAX_MAX - BITS_PER_MP_LIMB &&
  68           e > f + BITS_PER_MP_LIMB)
  69         return si;
  70
  71       /* now f < e <= f + BITS_PER_MP_LIMB */
  72       c = (mp_limb_t) ai;
  73       count_leading_zeros(k, c);
  74       if ((int) (e - f) > BITS_PER_MP_LIMB - k)
  75         return si;
  76       if ((int) (e - f) < BITS_PER_MP_LIMB - k)
  77         return -si;
  78
  79       /* now b and i*2^f have the same exponent */
  80       c <<= k;
  81       bn = (MPFR_PREC(b) - 1) / BITS_PER_MP_LIMB;
  82       bp = MPFR_MANT(b);
  83       if (bp[bn] > c)
  84         return si;
  85       if (bp[bn] < c)
  86         return -si;
  87
  88       /* most significant limbs agree, check remaining limbs from b */
  89       while (bn > 0)
  90         if (bp[--bn])
  91           return si;
  92       return 0;
  93     }
  94 }
  95
  96 #undef mpfr_cmp_si
  97 int
  98 mpfr_cmp_si (mpfr_srcptr b, long int i)
  99 {
 100   return mpfr_cmp_si_2exp (b, i, 0);
 101 }