sysdeps/ieee754/dbl-64/wordsize-64/s_scalbln.c

   1 /* @(#)s_scalbn.c 5.1 93/09/24 */
   2 /*
   3  * ====================================================
   4  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
   5  *
   6  * Developed at SunPro, a Sun Microsystems, Inc. business.
   7  * Permission to use, copy, modify, and distribute this
   8  * software is freely granted, provided that this notice
   9  * is preserved.
  10  * ====================================================
  11  */
  12
  13 /*
  14  * scalbn (double x, int n)
  15  * scalbn(x,n) returns x* 2**n  computed by  exponent
  16  * manipulation rather than by actually performing an
  17  * exponentiation or a multiplication.
  18  */
  19
  20 #include "math.h"
  21 #include "math_private.h"
  22
  23 #ifdef __STDC__
  24 static const double
  25 #else
  26 static double
  27 #endif
  28 two54   =  1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */
  29 twom54  =  5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */
  30 huge   = 1.0e+300,
  31 tiny   = 1.0e-300;
  32
  33 #ifdef __STDC__
  34         double __scalbln (double x, long int n)
  35 #else
  36         double __scalbln (x,n)
  37         double x; long int n;
  38 #endif
  39 {
  40         int64_t ix;
  41         int64_t k;
  42         EXTRACT_WORDS64(ix,x);
  43         k = (ix >> 52) & 0x7ff;                 /* extract exponent */
  44         if (k==0) {                             /* 0 or subnormal x */
  45             if ((ix & UINT64_C(0xfffffffffffff))==0) return x; /* +-0 */
  46             x *= two54;
  47             EXTRACT_WORDS64(ix,x);
  48             k = ((ix >> 52) & 0x7ff) - 54;
  49             }
  50         if (k==0x7ff) return x+x;               /* NaN or Inf */
  51         k = k+n;
  52         if (n> 50000 || k >  0x7fe)
  53           return huge*__copysign(huge,x); /* overflow  */
  54         if (n< -50000) return tiny*__copysign(tiny,x); /*underflow*/
  55         if (k > 0)                              /* normal result */
  56             {INSERT_WORDS64(x,(ix&UINT64_C(0x800fffffffffffff))|(k<<52));
  57               return x;}
  58         if (k <= -54)
  59           return tiny*__copysign(tiny,x);       /*underflow*/
  60         k += 54;                                /* subnormal result */
  61         INSERT_WORDS64(x,(ix&INT64_C(0x800fffffffffffff))|(k<<52));
  62         return x*twom54;
  63 }
  64 weak_alias (__scalbln, scalbln)
  65 #ifdef NO_LONG_DOUBLE
  66 strong_alias (__scalbln, __scalblnl)
  67 weak_alias (__scalbln, scalblnl)
  68 #endif