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Annotation of OpenXM_contrib/gmp/insert-dbl.c, Revision 1.1.1.2

1.1.1.2 ! ohara       1: /* __gmp_scale2 -- Scale a double by exponent manipulation.
1.1       maekawa     2:
1.1.1.2 ! ohara       3: Copyright 1996, 1997, 1999, 2000, 2001, 2002 Free Software Foundation, Inc.
1.1       maekawa     4:
                      5: This file is part of the GNU MP Library.
                      6:
                      7: The GNU MP 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 GNU MP 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 GNU MP 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:
                     25: #ifdef XDEBUG
                     26: #undef _GMP_IEEE_FLOATS
                     27: #endif
                     28:
                     29: #ifndef _GMP_IEEE_FLOATS
                     30: #define _GMP_IEEE_FLOATS 0
                     31: #endif
                     32:
                     33: double
                     34: __gmp_scale2 (double d, int exp)
                     35: {
                     36: #if _GMP_IEEE_FLOATS
                     37:   {
                     38: #if defined (__alpha) && __GNUC__ == 2 && __GNUC_MINOR__ == 8
                     39:     /* Work around alpha-specific bug in GCC 2.8.x.  */
                     40:     volatile
                     41: #endif
                     42:     union ieee_double_extract x;
                     43:     x.d = d;
                     44:     exp += x.s.exp;
                     45:     x.s.exp = exp;
                     46:     if (exp >= 2047)
                     47:       {
                     48:        /* Return +-infinity */
                     49:        x.s.exp = 2047;
                     50:        x.s.manl = x.s.manh = 0;
                     51:       }
                     52:     else if (exp < 1)
                     53:       {
                     54:        x.s.exp = 1;            /* smallest exponent (biased) */
                     55:        /* Divide result by 2 until we have scaled it to the right IEEE
                     56:           denormalized number, but stop if it becomes zero.  */
                     57:        while (exp < 1 && x.d != 0)
                     58:          {
                     59:            x.d *= 0.5;
                     60:            exp++;
                     61:          }
                     62:       }
                     63:     return x.d;
                     64:   }
                     65: #else
                     66:   {
                     67:     double factor, r;
                     68:
                     69:     factor = 2.0;
                     70:     if (exp < 0)
                     71:       {
                     72:        factor = 0.5;
                     73:        exp = -exp;
                     74:       }
                     75:     r = d;
                     76:     if (exp != 0)
                     77:       {
                     78:        if ((exp & 1) != 0)
                     79:          r *= factor;
                     80:        exp >>= 1;
                     81:        while (exp != 0)
                     82:          {
                     83:            factor *= factor;
                     84:            if ((exp & 1) != 0)
                     85:              r *= factor;
                     86:            exp >>= 1;
                     87:          }
                     88:       }
                     89:     return r;
                     90:   }
                     91: #endif
                     92: }