contrib/mpfr/cmp_ui.c

   1 /* mpfr_cmp_ui_2exp -- compare a floating-point number with an unsigned
   2 machine integer multiplied by a power of 2
   3
   4 Copyright 1999, 2001, 2002, 2003, 2004, 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_ui_2exp (mpfr_srcptr b, unsigned long int i, mp_exp_t f)
  35 {
  36   if (MPFR_UNLIKELY( MPFR_IS_SINGULAR(b) ))
  37     {
  38       if (MPFR_IS_NAN (b))
  39         {
  40           MPFR_SET_ERANGE ();
  41           return 0;
  42         }
  43       else if (MPFR_IS_INF(b))
  44         return MPFR_INT_SIGN (b);
  45       else /* since b cannot be NaN, b=0 here */
  46         return i != 0 ? -1 : 0;
  47     }
  48
  49   if (MPFR_IS_NEG (b))
  50     return -1;
  51   /* now b > 0 */
  52   else if (MPFR_UNLIKELY(i == 0))
  53     return 1;
  54   else /* b > 0, i > 0 */
  55     {
  56       mp_exp_t e;
  57       int k;
  58       mp_size_t bn;
  59       mp_limb_t c, *bp;
  60
  61       /* i must be representable in a mp_limb_t */
  62       MPFR_ASSERTN(i == (mp_limb_t) i);
  63
  64       e = MPFR_GET_EXP (b); /* 2^(e-1) <= b < 2^e */
  65       if (e <= f)
  66         return -1;
  67       if (f < MPFR_EMAX_MAX - BITS_PER_MP_LIMB &&
  68           e > f + BITS_PER_MP_LIMB)
  69         return 1;
  70
  71       /* now f < e <= f + BITS_PER_MP_LIMB */
  72       c = (mp_limb_t) i;
  73       count_leading_zeros(k, c);
  74       if ((int) (e - f) > BITS_PER_MP_LIMB - k)
  75         return 1;
  76       if ((int) (e - f) < BITS_PER_MP_LIMB - k)
  77         return -1;
  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 1;
  85       if (bp[bn] < c)
  86         return -1;
  87
  88       /* most significant limbs agree, check remaining limbs from b */
  89       while (bn > 0)
  90         if (bp[--bn] != 0)
  91           return 1;
  92       return 0;
  93     }
  94 }
  95
  96 #undef mpfr_cmp_ui
  97 int
  98 mpfr_cmp_ui (mpfr_srcptr b, unsigned long int i)
  99 {
 100   return mpfr_cmp_ui_2exp (b, i, 0);
 101 }