libm/powerpc/classic/s_frexp.c

   1 /*******************************************************************************
   2 *                                                                              *
   3 *      File frexpldexp.c,                                                      *
   4 *      Functions frexp(x) and ldexp(x),                                        *
   5 *      Implementation of frexp and ldexp functions for the PowerPC.            *
   6 *                                                                              *
   7 *      Copyright © 1991 Apple Computer, Inc.  All rights reserved.             *
   8 *                                                                              *
   9 *      Written by Ali Sazegari, started on January 1991,                       *
  10 *                                                                              *
  11 *      W A R N I N G:  This routine expects a 64 bit double model.             *
  12 *                                                                              *
  13 *      December03 1992: first rs6000 implementation.                           *
  14 *      October 05 1993: added special cases for NaN and ° in frexp.            *
  15 *      May     27 1997: improved the performance of frexp by eliminating the   *
  16 *                       switch statement.                                      *
  17 *        June      13 2001: (ram) rewrote frexp to eliminate calls to scalb and    *
  18 *                               logb.                                                                    *
  19 *                                                                              *
  20 *******************************************************************************/
  21
  22 #include <limits.h>
  23 #include <math.h>
  24 #include <endian.h>
  25
  26 static const double two54 =  1.80143985094819840000e+16; /* 0x43500000, 0x00000000 */
  27
  28 typedef union
  29       {
  30       struct {
  31 #if (__BYTE_ORDER == __BIG_ENDIAN)
  32         unsigned long int hi;
  33         unsigned long int lo;
  34 #else
  35         unsigned long int lo;
  36         unsigned long int hi;
  37 #endif
  38       } words;
  39       double dbl;
  40       } DblInHex;
  41
  42 libm_hidden_proto(frexp)
  43 double frexp ( double value, int *eptr )
  44       {
  45       DblInHex argument;
  46       unsigned long int valueHead;
  47
  48       argument.dbl = value;
  49       valueHead = argument.words.hi & 0x7fffffffUL; // valueHead <- |x|
  50
  51       *eptr = 0;
  52         if ( valueHead >= 0x7ff00000 || ( valueHead | argument.words.lo ) == 0 )
  53                 return value;           // 0, inf, or NaN
  54
  55         if ( valueHead < 0x00100000 )
  56                 {       // denorm
  57                 argument.dbl = two54 * value;
  58                 valueHead = argument.words.hi &0x7fffffff;
  59                 *eptr = -54;
  60                 }
  61         *eptr += ( valueHead >> 20 ) - 1022;
  62         argument.words.hi = ( argument.words.hi & 0x800fffff ) | 0x3fe00000;
  63         return argument.dbl;
  64         }
  65 libm_hidden_def(frexp)