base/math/frexpldexp.c

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#if defined(__ppc__)
/*******************************************************************************
*                                                                              *
*      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 ldexp ( double value, int exp ) 
      {
      if ( exp > SHRT_MAX ) 
            exp = SHRT_MAX;
      else if ( exp < -SHRT_MAX ) 
            exp = -SHRT_MAX;
      return scalb ( value, exp  );
      }

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;
    }
#endif /* __ppc__ */

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