compiler/mlib/s_scalbnl.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_scalbnl.c,v 1.1 2005/03/07 04:52:58 das Exp $";
  15 #endif
  16
  17 /*
  18  * scalbnl (long double x, int n)
  19  * scalbnl(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 /*
  25  * We assume that a long double has a 15-bit exponent.  On systems
  26  * where long double is the same as double, scalbnl() is an alias
  27  * for scalbn(), so we don't use this routine.
  28  */
  29
  30 #include <sys/cdefs.h>
  31 #include <float.h>
  32 #include <math.h>
  33
  34 #include "fpmath.h"
  35
  36 #if LDBL_MAX_EXP != 0x4000
  37 #error "Unsupported long double format"
  38 #endif
  39
  40 static const long double
  41 huge = 0x1p16000L,
  42 tiny = 0x1p-16000L;
  43
  44 long double
  45 scalbnl (long double x, int n)
  46 {
  47         union IEEEl2bits u;
  48         int k;
  49         u.e = x;
  50         k = u.bits.exp;                         /* extract exponent */
  51         if (k==0) {                             /* 0 or subnormal x */
  52             if ((u.bits.manh|u.bits.manl)==0) return x; /* +-0 */
  53             u.e *= 0x1p+128;
  54             k = u.bits.exp - 128;
  55             if (n< -50000) return tiny*x;       /*underflow*/
  56             }
  57         if (k==0x7fff) return x+x;              /* NaN or Inf */
  58         k = k+n;
  59         if (k >= 0x7fff) return huge*copysignl(huge,x); /* overflow  */
  60         if (k > 0)                              /* normal result */
  61             {u.bits.exp = k; return u.e;}
  62         if (k <= -128)
  63             if (n > 50000)      /* in case integer overflow in n+k */
  64                 return huge*copysign(huge,x);   /*overflow*/
  65             else return tiny*copysign(tiny,x);  /*underflow*/
  66         k += 128;                               /* subnormal result */
  67         u.bits.exp = k;
  68         return u.e*0x1p-128;
  69 }
  70
  71 __strong_reference(scalbnl, ldexpl);