libquadmath/math/scalblnq.c

   1 /* scalblnq.c -- __float128 version of s_scalbn.c.
   2  * Conversion to IEEE quad long double by Jakub Jelinek, jj@ultra.linux.cz.
   3  */
   4
   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 /*
  17  * scalblnq (_float128 x, long int n)
  18  * scalblnq(x,n) returns x* 2**n  computed by  exponent
  19  * manipulation rather than by actually performing an
  20  * exponentiation or a multiplication.
  21  */
  22
  23 #include "quadmath-imp.h"
  24
  25 static const __float128
  26 two114 = 2.0769187434139310514121985316880384E+34Q, /* 0x4071000000000000, 0 */
  27 twom114 = 4.8148248609680896326399448564623183E-35Q, /* 0x3F8D000000000000, 0 */
  28 huge   = 1.0E+4900Q,
  29 tiny   = 1.0E-4900Q;
  30
  31 __float128
  32 scalblnq (__float128 x, long int n)
  33 {
  34         int64_t k,hx,lx;
  35         GET_FLT128_WORDS64(hx,lx,x);
  36         k = (hx>>48)&0x7fff;            /* extract exponent */
  37         if (k==0) {                             /* 0 or subnormal x */
  38             if ((lx|(hx&0x7fffffffffffffffULL))==0) return x; /* +-0 */
  39             x *= two114;
  40             GET_FLT128_MSW64(hx,x);
  41             k = ((hx>>48)&0x7fff) - 114;
  42         }
  43         if (k==0x7fff) return x+x;              /* NaN or Inf */
  44         if (n< -50000) return tiny*copysignq(tiny,x); /*underflow*/
  45         if (n> 50000 || k+n > 0x7ffe)
  46           return huge*copysignq(huge,x); /* overflow  */
  47         /* Now k and n are bounded we know that k = k+n does not
  48            overflow.  */
  49         k = k+n;
  50         if (k > 0)                              /* normal result */
  51             {SET_FLT128_MSW64(x,(hx&0x8000ffffffffffffULL)|(k<<48)); return x;}
  52         if (k <= -114)
  53           return tiny*copysignq(tiny,x);        /*underflow*/
  54         k += 114;                               /* subnormal result */
  55         SET_FLT128_MSW64(x,(hx&0x8000ffffffffffffULL)|(k<<48));
  56         return x*twom114;
  57 }