sysdeps/ieee754/ldbl-128/s_scalblnl.c

   1 /* s_scalblnl.c -- long double version of s_scalbn.c.
   2  */
   3
   4 /* @(#)s_scalbn.c 5.1 93/09/24 */
   5 /*
   6  * ====================================================
   7  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
   8  *
   9  * Developed at SunPro, a Sun Microsystems, Inc. business.
  10  * Permission to use, copy, modify, and distribute this
  11  * software is freely granted, provided that this notice
  12  * is preserved.
  13  * ====================================================
  14  */
  15
  16 #if defined(LIBM_SCCS) && !defined(lint)
  17 static char rcsid[] = "$NetBSD: $";
  18 #endif
  19
  20 /*
  21  * scalblnl (long double x, long int n)
  22  * scalblnl(x,n) returns x* 2**n  computed by  exponent
  23  * manipulation rather than by actually performing an
  24  * exponentiation or a multiplication.
  25  */
  26
  27 #include <math.h>
  28 #include <math_private.h>
  29
  30 static const _Float128
  31 two114 = L(2.0769187434139310514121985316880384E+34), /* 0x4071000000000000, 0 */
  32 twom114 = L(4.8148248609680896326399448564623183E-35), /* 0x3F8D000000000000, 0 */
  33 huge   = L(1.0E+4900),
  34 tiny   = L(1.0E-4900);
  35
  36 _Float128 __scalblnl (_Float128 x, long int n)
  37 {
  38         int64_t k,hx,lx;
  39         GET_LDOUBLE_WORDS64(hx,lx,x);
  40         k = (hx>>48)&0x7fff;            /* extract exponent */
  41         if (k==0) {                             /* 0 or subnormal x */
  42             if ((lx|(hx&0x7fffffffffffffffULL))==0) return x; /* +-0 */
  43             x *= two114;
  44             GET_LDOUBLE_MSW64(hx,x);
  45             k = ((hx>>48)&0x7fff) - 114;
  46         }
  47         if (k==0x7fff) return x+x;              /* NaN or Inf */
  48         if (n< -50000) return tiny*copysignl(tiny,x); /*underflow*/
  49         if (n> 50000 || k+n > 0x7ffe)
  50           return huge*copysignl(huge,x); /* overflow  */
  51         /* Now k and n are bounded we know that k = k+n does not
  52            overflow.  */
  53         k = k+n;
  54         if (k > 0)                              /* normal result */
  55             {SET_LDOUBLE_MSW64(x,(hx&0x8000ffffffffffffULL)|(k<<48)); return x;}
  56         if (k <= -114)
  57           return tiny*copysignl(tiny,x);        /*underflow*/
  58         k += 114;                               /* subnormal result */
  59         SET_LDOUBLE_MSW64(x,(hx&0x8000ffffffffffffULL)|(k<<48));
  60         return x*twom114;
  61 }