lib/libm/src/s_frexp.c

   1 /* @(#)s_frexp.c 5.1 93/09/24 */
   2 /*
   3  * ====================================================
   4  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
   5  *
   6  * Developed at SunPro, a Sun Microsystems, Inc. business.
   7  * Permission to use, copy, modify, and distribute this
   8  * software is freely granted, provided that this notice
   9  * is preserved.
  10  * ====================================================
  11  */
  12
  13 #include <sys/cdefs.h>
  14 #if defined(LIBM_SCCS) && !defined(lint)
  15 __RCSID("$NetBSD: s_frexp.c,v 1.13 2008/09/28 18:54:55 christos Exp $");
  16 #endif
  17
  18 /*
  19  * for non-zero x
  20  *      x = frexp(arg,&exp);
  21  * return a double fp quantity x such that 0.5 <= |x| <1.0
  22  * and the corresponding binary exponent "exp". That is
  23  *      arg = x*2^exp.
  24  * If arg is inf, 0.0, or NaN, then frexp(arg,&exp) returns arg
  25  * with *exp=0.
  26  */
  27
  28 #include "math.h"
  29 #include "math_private.h"
  30
  31 static const double
  32 two54 =  1.80143985094819840000e+16; /* 0x43500000, 0x00000000 */
  33
  34 double
  35 frexp(double x, int *eptr)
  36 {
  37         int32_t hx, ix, lx;
  38         EXTRACT_WORDS(hx,lx,x);
  39         ix = 0x7fffffff&hx;
  40         *eptr = 0;
  41         if(ix>=0x7ff00000||((ix|lx)==0)) return x;      /* 0,inf,nan */
  42         if (ix<0x00100000) {            /* subnormal */
  43             x *= two54;
  44             GET_HIGH_WORD(hx,x);
  45             ix = hx&0x7fffffff;
  46             *eptr = -54;
  47         }
  48         *eptr += ((uint32_t)ix>>20)-1022;
  49         hx = (hx&0x800fffff)|0x3fe00000;
  50         SET_HIGH_WORD(x,hx);
  51         return x;
  52 }