sysdeps/ieee754/ldbl-128ibm/s_scalbnl.c

   1 /* s_scalbnl.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  * scalbnl (long double x, int n)
  22  * scalbnl(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 #include <math_ldbl_opt.h>
  30
  31 static const long double
  32 twolm54 = 5.55111512312578270212e-17, /* 0x3C90000000000000, 0 */
  33 huge   = 1.0E+300L,
  34 tiny   = 1.0E-300L;
  35 static const double
  36 two54 = 1.80143985094819840000e+16, /* 0x4350000000000000 */
  37 twom54 = 5.55111512312578270212e-17; /* 0x3C90000000000000 */
  38
  39 long double __scalbnl (long double x, int n)
  40 {
  41         int64_t k,l,hx,lx;
  42         union { int64_t i; double d; } u;
  43         double xhi, xlo;
  44
  45         ldbl_unpack (x, &xhi, &xlo);
  46         EXTRACT_WORDS64 (hx, xhi);
  47         EXTRACT_WORDS64 (lx, xlo);
  48         k = (hx>>52)&0x7ff;             /* extract exponent */
  49         l = (lx>>52)&0x7ff;
  50         if (k==0) {                             /* 0 or subnormal x */
  51             if ((hx&0x7fffffffffffffffULL)==0) return x; /* +-0 */
  52             u.i = hx;
  53             u.d *= two54;
  54             hx = u.i;
  55             k = ((hx>>52)&0x7ff) - 54;
  56         }
  57         else if (k==0x7ff) return x+x;          /* NaN or Inf */
  58         if (n< -50000) return tiny*copysignl(tiny,x); /*underflow */
  59         if (n> 50000 || k+n > 0x7fe)
  60           return huge*copysignl(huge,x); /* overflow */
  61         /* Now k and n are bounded we know that k = k+n does not
  62            overflow.  */
  63         k = k+n;
  64         if (k > 0) {                            /* normal result */
  65             hx = (hx&0x800fffffffffffffULL)|(k<<52);
  66             if ((lx & 0x7fffffffffffffffULL) == 0) { /* low part +-0 */
  67                 INSERT_WORDS64 (xhi, hx);
  68                 INSERT_WORDS64 (xlo, lx);
  69                 x = ldbl_pack (xhi, xlo);
  70                 return x;
  71             }
  72             if (l == 0) { /* low part subnormal */
  73                 u.i = lx;
  74                 u.d *= two54;
  75                 lx = u.i;
  76                 l = ((lx>>52)&0x7ff) - 54;
  77             }
  78             l = l + n;
  79             if (l > 0)
  80                 lx = (lx&0x800fffffffffffffULL)|(l<<52);
  81             else if (l <= -54)
  82                 lx = (lx&0x8000000000000000ULL);
  83             else {
  84                 l += 54;
  85                 u.i = (lx&0x800fffffffffffffULL)|(l<<52);
  86                 u.d *= twom54;
  87                 lx = u.i;
  88             }
  89             INSERT_WORDS64 (xhi, hx);
  90             INSERT_WORDS64 (xlo, lx);
  91             x = ldbl_pack (xhi, xlo);
  92             return x;
  93         }
  94         if (k <= -54)
  95           return tiny*copysignl(tiny,x);        /*underflow*/
  96         k += 54;                                /* subnormal result */
  97         lx &= 0x8000000000000000ULL;
  98         hx &= 0x800fffffffffffffULL;
  99         INSERT_WORDS64 (xhi, hx|(k<<52));
 100         INSERT_WORDS64 (xlo, lx);
 101         x = ldbl_pack (xhi, xlo);
 102         return x*twolm54;
 103 }