newlib/libm/mathfp/s_frexp.c

   1
   2 /* @(#)z_frexp.c 1.0 98/08/13 */
   3
   4 /*
   5 FUNCTION
   6        <<frexp>>, <<frexpf>>---split floating-point number
   7 INDEX
   8         frexp
   9 INDEX
  10         frexpf
  11
  12 SYNOPSIS
  13         #include <math.h>
  14         double frexp(double <[val]>, int *<[exp]>);
  15         float frexpf(float <[val]>, int *<[exp]>);
  16
  17 DESCRIPTION
  18         All nonzero, normal numbers can be described as <[m]> * 2**<[p]>.
  19         <<frexp>> represents the double <[val]> as a mantissa <[m]>
  20         and a power of two <[p]>. The resulting mantissa will always
  21         be greater than or equal to <<0.5>>, and less than <<1.0>> (as
  22         long as <[val]> is nonzero). The power of two will be stored
  23         in <<*>><[exp]>.
  24
  25 @ifnottex
  26 <[m]> and <[p]> are calculated so that
  27 <[val]> is <[m]> times <<2>> to the power <[p]>.
  28 @end ifnottex
  29 @tex
  30 <[m]> and <[p]> are calculated so that
  31 $ val = m \times 2^p $.
  32 @end tex
  33
  34 <<frexpf>> is identical, other than taking and returning
  35 floats rather than doubles.
  36
  37 RETURNS
  38 <<frexp>> returns the mantissa <[m]>. If <[val]> is <<0>>, infinity,
  39 or Nan, <<frexp>> will set <<*>><[exp]> to <<0>> and return <[val]>.
  40
  41 PORTABILITY
  42 <<frexp>> is ANSI.
  43 <<frexpf>> is an extension.
  44
  45
  46 */
  47
  48 /*****************************************************************
  49  * frexp
  50  *
  51  * Input:
  52  *   d   - floating point value
  53  *   exp - exponent value
  54  *
  55  * Output:
  56  *   A floating point value in the range [0.5, 1).
  57  *
  58  * Description:
  59  *   This routine breaks a floating point value into a number f and
  60  *   an exponent exp such that d = f * 2 ^ exp.
  61  *
  62  *****************************************************************/
  63
  64 #include "fdlibm.h"
  65 #include "zmath.h"
  66
  67 #ifndef _DOUBLE_IS_32BITS
  68
  69 double frexp (double d, int *exp)
  70 {
  71   double f;
  72   __uint32_t hd, ld, hf, lf;
  73
  74   /* Check for special values. */
  75   switch (numtest (d))
  76     {
  77       case NAN:
  78       case INF:
  79         errno = EDOM;
  80       case 0:
  81         *exp = 0;
  82         return (d);
  83     }
  84
  85   EXTRACT_WORDS (hd, ld, d);
  86
  87   /* Get the exponent. */
  88   *exp = ((hd & 0x7ff00000) >> 20) - 1022;
  89
  90   /* Get the mantissa. */
  91   lf = ld;
  92   hf = hd & 0x800fffff;
  93   hf |= 0x3fe00000;
  94
  95   INSERT_WORDS (f, hf, lf);
  96
  97   return (f);
  98 }
  99
 100 #endif /* _DOUBLE_IS_32BITS */