newlib/libm/mathfp/s_ldexp.c

   1
   2 /* @(#)z_ldexp.c 1.0 98/08/13 */
   3
   4 /*
   5 FUNCTION
   6        <<ldexp>>, <<ldexpf>>---load exponent
   7
   8 INDEX
   9         ldexp
  10 INDEX
  11         ldexpf
  12
  13 SYNOPSIS
  14        #include <math.h>
  15        double ldexp(double <[val]>, int <[exp]>);
  16        float ldexpf(float <[val]>, int <[exp]>);
  17
  18 DESCRIPTION
  19 <<ldexp>> calculates the value
  20 @ifnottex
  21 <[val]> times 2 to the power <[exp]>.
  22 @end ifnottex
  23 @tex
  24 $val\times 2^{exp}$.
  25 @end tex
  26 <<ldexpf>> is identical, save that it takes and returns <<float>>
  27 rather than <<double>> values.
  28
  29 RETURNS
  30 <<ldexp>> returns the calculated value.
  31
  32 Underflow and overflow both set <<errno>> to <<ERANGE>>.
  33 On underflow, <<ldexp>> and <<ldexpf>> return 0.0.
  34 On overflow, <<ldexp>> returns plus or minus <<HUGE_VAL>>.
  35
  36 PORTABILITY
  37 <<ldexp>> is ANSI. <<ldexpf>> is an extension.
  38
  39 */
  40
  41 /******************************************************************
  42  * ldexp
  43  *
  44  * Input:
  45  *   d - a floating point value
  46  *   e - an exponent value
  47  *
  48  * Output:
  49  *   A floating point value f such that f = d * 2 ^ e.
  50  *
  51  * Description:
  52  *   This function creates a floating point number f such that
  53  *   f = d * 2 ^ e.
  54  *
  55  *****************************************************************/
  56
  57 #include <float.h>
  58 #include "fdlibm.h"
  59 #include "zmath.h"
  60
  61 #ifndef _DOUBLE_IS_32BITS
  62
  63 #define DOUBLE_EXP_OFFS 1023
  64
  65 double
  66 ldexp (double d,
  67         int e)
  68 {
  69   int exp;
  70   __uint32_t hd;
  71
  72   GET_HIGH_WORD (hd, d);
  73
  74   /* Check for special values and then scale d by e. */
  75   switch (numtest (d))
  76     {
  77       case NAN:
  78         errno = EDOM;
  79         break;
  80
  81       case INF:
  82         errno = ERANGE;
  83         break;
  84
  85       case 0:
  86         break;
  87
  88       default:
  89         exp = (hd & 0x7ff00000) >> 20;
  90         exp += e;
  91
  92         if (exp > DBL_MAX_EXP + DOUBLE_EXP_OFFS)
  93          {
  94            errno = ERANGE;
  95            d = z_infinity.d;
  96          }
  97         else if (exp < DBL_MIN_EXP + DOUBLE_EXP_OFFS)
  98          {
  99            errno = ERANGE;
 100            d = -z_infinity.d;
 101          }
 102         else
 103          {
 104            hd &= 0x800fffff;
 105            hd |= exp << 20;
 106            SET_HIGH_WORD (d, hd);
 107          }
 108     }
 109
 110     return (d);
 111 }
 112
 113 #endif /* _DOUBLE_IS_32BITS */