sysdeps/ieee754/ldbl-96/s_scalblnl.c

   1 /* s_scalbnl.c -- long double version of s_scalbn.c.
   2  */
   3
   4 /*
   5  * ====================================================
   6  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
   7  *
   8  * Developed at SunPro, a Sun Microsystems, Inc. business.
   9  * Permission to use, copy, modify, and distribute this
  10  * software is freely granted, provided that this notice
  11  * is preserved.
  12  * ====================================================
  13  */
  14
  15 /*
  16  * scalbnl (long double x, int n)
  17  * scalbnl(x,n) returns x* 2**n  computed by  exponent
  18  * manipulation rather than by actually performing an
  19  * exponentiation or a multiplication.
  20  */
  21
  22 #include <math.h>
  23 #include <math_private.h>
  24
  25 static const long double
  26 two63   =  0x1p63L,
  27 twom64  =  0x1p-64L,
  28 huge   = 1.0e+4900L,
  29 tiny   = 1.0e-4900L;
  30
  31 long double
  32 __scalblnl (long double x, long int n)
  33 {
  34         int32_t k,es,hx,lx;
  35         GET_LDOUBLE_WORDS(es,hx,lx,x);
  36         k = es&0x7fff;                          /* extract exponent */
  37         if (__builtin_expect(k==0, 0)) {        /* 0 or subnormal x */
  38             if ((lx|(hx&0x7fffffff))==0) return x; /* +-0 */
  39             x *= two63;
  40             GET_LDOUBLE_EXP(es,x);
  41             k = (es&0x7fff) - 63;
  42             }
  43         if (__builtin_expect(k==0x7fff, 0)) return x+x; /* NaN or Inf */
  44         if (__builtin_expect(n< -50000, 0))
  45           return tiny*copysignl(tiny,x);
  46         if (__builtin_expect(n> 50000 || k+n > 0x7ffe, 0))
  47           return huge*copysignl(huge,x); /* overflow  */
  48         /* Now k and n are bounded we know that k = k+n does not
  49            overflow.  */
  50         k = k+n;
  51         if (__builtin_expect(k > 0, 1))         /* normal result */
  52             {SET_LDOUBLE_EXP(x,(es&0x8000)|k); return x;}
  53         if (k <= -64)
  54             return tiny*copysignl(tiny,x);      /*underflow*/
  55         k += 64;                                /* subnormal result */
  56         SET_LDOUBLE_EXP(x,(es&0x8000)|k);
  57         return x*twom64;
  58 }