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/*******************************************************************************

*                                                                              *

*      File frexpldexp.c,                                                      *

*      Functions frexp(x) and ldexp(x),                                        *

*      Implementation of frexp and ldexp functions for the PowerPC.            *

*                                                                              *

*      Copyright © 1991 Apple Computer, Inc.  All rights reserved.             *

*                                                                              *

*      Written by Ali Sazegari, started on January 1991,                       *

*                                                                              *

*      W A R N I N G:  This routine expects a 64 bit double model.             *

*                                                                              *

*      December03 1992: first rs6000 implementation.                           *

*      October 05 1993: added special cases for NaN and ° in frexp.            *

*      May     27 1997: improved the performance of frexp by eliminating the   *

*                       switch statement.                                      *

*        June      13 2001: (ram) rewrote frexp to eliminate calls to scalb and    *

*                               logb.                                                                    *

*                                                                              *

*******************************************************************************/

#include <limits.h>

#include <math.h>

static const double two54 =  1.80143985094819840000e+16; /* 0x43500000, 0x00000000 */

typedef union

      {

      struct {

#if defined(__BIG_ENDIAN__)

        unsigned long int hi;

        unsigned long int lo;

#else

        unsigned long int lo;

        unsigned long int hi;

#endif

      } words;

      double dbl;

      } DblInHex;

double frexp ( double value, int *eptr )

      {

      DblInHex argument;

      unsigned long int valueHead;

      argument.dbl = value;

      valueHead = argument.words.hi & 0x7fffffffUL; // valueHead <- |x|

      *eptr = 0;

        if ( valueHead >= 0x7ff00000 || ( valueHead | argument.words.lo ) == 0 )

                return value;           // 0, inf, or NaN

        if ( valueHead < 0x00100000 )

                {       // denorm

                argument.dbl = two54 * value;

                valueHead = argument.words.hi &0x7fffffff;

                *eptr = -54;

                }

        *eptr += ( valueHead >> 20 ) - 1022;

        argument.words.hi = ( argument.words.hi & 0x800fffff ) | 0x3fe00000;

        return argument.dbl;

        }