sysdeps/libm-ieee754/s_scalbnl.c

   1 /* s_scalbnl.c -- long double version of s_scalbn.c.
   2  * Conversion to long double by Ulrich Drepper,
   3  * Cygnus Support, drepper@cygnus.com.
   4  */
   5
   6 /*
   7  * ====================================================
   8  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
   9  *
  10  * Developed at SunPro, a Sun Microsystems, Inc. business.
  11  * Permission to use, copy, modify, and distribute this
  12  * software is freely granted, provided that this notice
  13  * is preserved.
  14  * ====================================================
  15  */
  16
  17 #if defined(LIBM_SCCS) && !defined(lint)
  18 static char rcsid[] = "$NetBSD: $";
  19 #endif
  20
  21 /*
  22  * scalbnl (long double x, int n)
  23  * scalbnl(x,n) returns x* 2**n  computed by  exponent
  24  * manipulation rather than by actually performing an
  25  * exponentiation or a multiplication.
  26  */
  27
  28 #include "math.h"
  29 #include "math_private.h"
  30
  31 #ifdef __STDC__
  32 static const long double
  33 #else
  34 static long double
  35 #endif
  36 two54   =  1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */
  37 twom54  =  5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */
  38 huge   = 1.0e+300,
  39 tiny   = 1.0e-300;
  40
  41 #ifdef __STDC__
  42         long double __scalbnl (long double x, int n)
  43 #else
  44         long double __scalbnl (x,n)
  45         long double x; int n;
  46 #endif
  47 {
  48         int32_t k,es,hx,lx;
  49         GET_LDOUBLE_WORDS(es,hx,lx,x);
  50         k = es&0x7fff;                          /* extract exponent */
  51         if (k==0) {                             /* 0 or subnormal x */
  52             if ((lx|(hx&0x7fffffff))==0) return x; /* +-0 */
  53             x *= two54;
  54             GET_HIGH_WORD(hx,x);
  55             k = ((hx&0x7ff00000)>>20) - 54;
  56             if (n< -50000) return tiny*x;       /*underflow*/
  57             }
  58         if (k==0x7ff) return x+x;               /* NaN or Inf */
  59         k = k+n;
  60         if (k >  0x7fe) return huge*__copysign(huge,x); /* overflow  */
  61         if (k > 0)                              /* normal result */
  62             {SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20)); return x;}
  63         if (k <= -54)
  64             if (n > 50000)      /* in case integer overflow in n+k */
  65                 return huge*__copysign(huge,x); /*overflow*/
  66             else return tiny*__copysign(tiny,x);        /*underflow*/
  67         k += 54;                                /* subnormal result */
  68         SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20));
  69         return x*twom54;
  70 }
  71 weak_alias (__scalbnl, scalbnl)