libm/powerpc/classic/s_trunc.c

   1 #include <limits.h>
   2 #include <math.h>
   3 #include <endian.h>
   4
   5 typedef union
   6       {
   7       struct {
   8 #if (__BYTE_ORDER == __BIG_ENDIAN)
   9         unsigned long int hi;
  10         unsigned long int lo;
  11 #else
  12         unsigned long int lo;
  13         unsigned long int hi;
  14 #endif
  15       } words;
  16       double dbl;
  17       } DblInHex;
  18
  19 static const unsigned long int signMask = 0x80000000ul;
  20 static const double twoTo52      = 4503599627370496.0;
  21
  22 /*******************************************************************************
  23 *                                                                              *
  24 *     The function trunc truncates its double argument to integral value       *
  25 *     and returns the result in double format.  This function signals          *
  26 *     inexact if an ordered return value is not equal to the operand.          *
  27 *                                                                              *
  28 *******************************************************************************/
  29
  30 libm_hidden_proto(trunc)
  31 double trunc ( double x )
  32       {
  33         DblInHex argument,OldEnvironment;
  34         register double y;
  35         register unsigned long int xhi;
  36         register long int target;
  37
  38         argument.dbl = x;
  39         xhi = argument.words.hi & 0x7fffffffUL;         // xhi <- high half of |x|
  40         target = ( argument.words.hi < signMask );              // flag positive sign
  41
  42         if ( xhi < 0x43300000ul )
  43 /*******************************************************************************
  44 *     Is |x| < 2.0^53?                                                         *
  45 *******************************************************************************/
  46                 {
  47                 if ( xhi < 0x3ff00000ul )
  48 /*******************************************************************************
  49 *     Is |x| < 1.0?                                                            *
  50 *******************************************************************************/
  51                         {
  52                         if ( ( xhi | argument.words.lo ) != 0ul )
  53                                 {                               // raise deserved INEXACT
  54                                 __asm__ ("mffs %0" : "=f" (OldEnvironment.dbl));
  55                                 OldEnvironment.words.lo |= 0x02000000ul;
  56                                 __asm__ ("mtfsf 255,%0" : /*NULLOUT*/ : /*IN*/ "f" ( OldEnvironment.dbl ));
  57                                 }
  58                         if ( target )                           // return properly signed zero
  59                                 return ( 0.0 );
  60                         else
  61                                 return ( -0.0 );
  62                         }
  63 /*******************************************************************************
  64 *     Is 1.0 < |x| < 2.0^52?                                                   *
  65 *******************************************************************************/
  66                 if ( target )
  67                         {
  68                         y = ( x + twoTo52 ) - twoTo52;          // round at binary point
  69                         if ( y > x )
  70                                 return ( y - 1.0 );
  71                         else
  72                                 return ( y );
  73                         }
  74
  75                 else
  76                         {
  77                         y = ( x - twoTo52 ) + twoTo52;          // round at binary point.
  78                         if ( y < x )
  79                                 return ( y + 1.0 );
  80                         else
  81                                 return ( y );
  82                         }
  83                 }
  84 /*******************************************************************************
  85 *      Is |x| >= 2.0^52 or x is a NaN.                                         *
  86 *******************************************************************************/
  87         return ( x );
  88         }
  89 libm_hidden_def(trunc)