libm/s_frexp.c

   1 /*
   2  * ====================================================
   3  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
   4  *
   5  * Developed at SunPro, a Sun Microsystems, Inc. business.
   6  * Permission to use, copy, modify, and distribute this
   7  * software is freely granted, provided that this notice
   8  * is preserved.
   9  * ====================================================
  10  */
  11
  12 /*
  13  * for non-zero x
  14  *      x = frexp(arg,&exp);
  15  * return a double fp quantity x such that 0.5 <= |x| <1.0
  16  * and the corresponding binary exponent "exp". That is
  17  *      arg = x*2^exp.
  18  * If arg is inf, 0.0, or NaN, then frexp(arg,&exp) returns arg
  19  * with *exp=0.
  20  */
  21
  22 #include "math.h"
  23 #include "math_private.h"
  24
  25 static const double
  26 two54 =  1.80143985094819840000e+16; /* 0x43500000, 0x00000000 */
  27
  28 double frexp(double x, int *eptr)
  29 {
  30         int32_t hx, ix, lx;
  31         EXTRACT_WORDS(hx,lx,x);
  32         ix = 0x7fffffff&hx;
  33         *eptr = 0;
  34         if(ix>=0x7ff00000||((ix|lx)==0)) return x;      /* 0,inf,nan */
  35         if (ix<0x00100000) {            /* subnormal */
  36             x *= two54;
  37             GET_HIGH_WORD(hx,x);
  38             ix = hx&0x7fffffff;
  39             *eptr = -54;
  40         }
  41         *eptr += (ix>>20)-1022;
  42         hx = (hx&0x800fffff)|0x3fe00000;
  43         SET_HIGH_WORD(x,hx);
  44         return x;
  45 }
  46 libm_hidden_def(frexp)