sysdeps/ieee754/dbl-64/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 #if defined(LIBM_SCCS) && !defined(lint)
  14 static char rcsid[] = "$NetBSD: s_frexp.c,v 1.9 1995/05/10 20:47:24 jtc Exp $";
  15 #endif
  16
  17 /*
  18  * for non-zero x
  19  *      x = frexp(arg,&exp);
  20  * return a double fp quantity x such that 0.5 <= |x| <1.0
  21  * and the corresponding binary exponent "exp". That is
  22  *      arg = x*2^exp.
  23  * If arg is inf, 0.0, or NaN, then frexp(arg,&exp) returns arg
  24  * with *exp=0.
  25  */
  26
  27 #include <math.h>
  28 #include <math_private.h>
  29
  30 static const double
  31   two54 = 1.80143985094819840000e+16; /* 0x43500000, 0x00000000 */
  32
  33 double
  34 __frexp (double x, int *eptr)
  35 {
  36   int32_t hx, ix, lx;
  37   EXTRACT_WORDS (hx, lx, x);
  38   ix = 0x7fffffff & hx;
  39   *eptr = 0;
  40   if (ix >= 0x7ff00000 || ((ix | lx) == 0))
  41     return x;                                           /* 0,inf,nan */
  42   if (ix < 0x00100000)                  /* subnormal */
  43     {
  44       x *= two54;
  45       GET_HIGH_WORD (hx, x);
  46       ix = hx & 0x7fffffff;
  47       *eptr = -54;
  48     }
  49   *eptr += (ix >> 20) - 1022;
  50   hx = (hx & 0x800fffff) | 0x3fe00000;
  51   SET_HIGH_WORD (x, hx);
  52   return x;
  53 }
  54 weak_alias (__frexp, frexp)
  55 #ifdef NO_LONG_DOUBLE
  56 strong_alias (__frexp, __frexpl)
  57 weak_alias (__frexp, frexpl)
  58 #endif