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Annotation of OpenXM_contrib/gmp/mpfr/div_2ui.c, Revision 1.1.1.1

1.1       ohara       1: /* mpfr_div_2ui -- divide a floating-point number by a power of two
                      2:
                      3: Copyright 1999, 2001 Free Software Foundation, Inc.
                      4:
                      5: This file is part of the MPFR Library.
                      6:
                      7: The MPFR Library is free software; you can redistribute it and/or modify
                      8: it under the terms of the GNU Lesser General Public License as published by
                      9: the Free Software Foundation; either version 2.1 of the License, or (at your
                     10: option) any later version.
                     11:
                     12: The MPFR Library is distributed in the hope that it will be useful, but
                     13: WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
                     14: or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
                     15: License for more details.
                     16:
                     17: You should have received a copy of the GNU Lesser General Public License
                     18: along with the MPFR Library; see the file COPYING.LIB.  If not, write to
                     19: the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
                     20: MA 02111-1307, USA. */
                     21:
                     22: #include "gmp.h"
                     23: #include "gmp-impl.h"
                     24: #include "mpfr.h"
                     25: #include "mpfr-impl.h"
                     26:
                     27: int
                     28: mpfr_div_2ui (mpfr_ptr y, mpfr_srcptr x, unsigned long int n, mp_rnd_t rnd_mode)
                     29: {
                     30:   int inexact;
                     31:
                     32:   inexact = y != x ? mpfr_set (y, x, rnd_mode) : 0;
                     33:
                     34:   if (MPFR_IS_FP(y) && MPFR_NOTZERO(y))
                     35:     {
                     36:       /* n will have to be casted to long to make sure that the addition
                     37:          and subtraction below (for overflow detection) are signed */
                     38:       while (n > LONG_MAX)
                     39:         {
                     40:           int inex2;
                     41:
                     42:           n -= LONG_MAX;
                     43:           inex2 = mpfr_div_2ui(y, y, LONG_MAX, rnd_mode);
                     44:           if (inex2)
                     45:             return inex2; /* underflow */
                     46:         }
                     47:
                     48:       /* MPFR_EMAX_MAX - (long) n is signed and doesn't lead to an overflow;
                     49:          the first test useful so that the real test can't lead to an
                     50:          overflow. */
                     51:       if (__mpfr_emin > MPFR_EMAX_MAX - (long) n ||
                     52:           MPFR_EXP(y) < __mpfr_emin + (long) n)
                     53:         return mpfr_set_underflow (y, rnd_mode, MPFR_SIGN(y));
                     54:
                     55:       MPFR_EXP(y) -= (long) n;
                     56:     }
                     57:
                     58:   return inexact;
                     59: }