compiler/mlib/s_scalbn.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 #ifndef lint
  14 static char rcsid[] = "$FreeBSD: src/lib/msun/src/s_scalbn.c,v 1.11 2005/03/07 21:27:37 das Exp $";
  15 #endif
  16
  17 /*
  18  * scalbn (double x, int n)
  19  * scalbn(x,n) returns x* 2**n  computed by  exponent
  20  * manipulation rather than by actually performing an
  21  * exponentiation or a multiplication.
  22  */
  23
  24 #include <sys/cdefs.h>
  25 #include <float.h>
  26
  27 #include "math.h"
  28 #include "math_private.h"
  29
  30 static const double
  31 two54   =  1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */
  32 twom54  =  5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */
  33 huge   = 1.0e+300,
  34 tiny   = 1.0e-300;
  35
  36 double
  37 scalbn (double x, int n)
  38 {
  39         int32_t k,hx,lx;
  40         EXTRACT_WORDS(hx,lx,x);
  41         k = (hx&0x7ff00000)>>20;                /* extract exponent */
  42         if (k==0) {                             /* 0 or subnormal x */
  43             if ((lx|(hx&0x7fffffff))==0) return x; /* +-0 */
  44             x *= two54;
  45             GET_HIGH_WORD(hx,x);
  46             k = ((hx&0x7ff00000)>>20) - 54;
  47             if (n< -50000) return tiny*x;       /*underflow*/
  48             }
  49         if (k==0x7ff) return x+x;               /* NaN or Inf */
  50         k = k+n;
  51         if (k >  0x7fe) return huge*copysign(huge,x); /* overflow  */
  52         if (k > 0)                              /* normal result */
  53             {SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20)); return x;}
  54         if (k <= -54)
  55             if (n > 50000)      /* in case integer overflow in n+k */
  56                 return huge*copysign(huge,x);   /*overflow*/
  57             else return tiny*copysign(tiny,x);  /*underflow*/
  58         k += 54;                                /* subnormal result */
  59         SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20));
  60         return x*twom54;
  61 }
  62
  63 #if (LDBL_MANT_DIG == 53)
  64 __weak_reference(scalbn, ldexpl);
  65 __weak_reference(scalbn, scalbnl);
  66 #endif
  67
  68 /* FreeBSD has ldexp() in libc */
  69 #ifdef __AROS__
  70 __strong_reference(scalbn, ldexp);
  71 #endif