lib/libm/src/s_scalbnl.c

   1 /*      $OpenBSD: s_scalbnl.c,v 1.2 2012/12/05 23:20:04 deraadt Exp $   */
   2 /* @(#)s_scalbn.c 5.1 93/09/24 */
   3 /*
   4  * ====================================================
   5  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
   6  *
   7  * Developed at SunPro, a Sun Microsystems, Inc. business.
   8  * Permission to use, copy, modify, and distribute this
   9  * software is freely granted, provided that this notice
  10  * is preserved.
  11  * ====================================================
  12  */
  13
  14 /*
  15  * scalbnl (long double x, int n)
  16  * scalbnl(x,n) returns x* 2**n  computed by  exponent
  17  * manipulation rather than by actually performing an
  18  * exponentiation or a multiplication.
  19  */
  20
  21 /*
  22  * We assume that a long double has a 15-bit exponent.  On systems
  23  * where long double is the same as double, scalbnl() is an alias
  24  * for scalbn(), so we don't use this routine.
  25  */
  26
  27 #include <sys/types.h>
  28 #include <machine/ieee.h>
  29 #include <float.h>
  30 #include <math.h>
  31
  32 #if LDBL_MAX_EXP != 0x4000
  33 #error "Unsupported long double format"
  34 #endif
  35
  36 static const long double
  37 huge = 0x1p16000L,
  38 tiny = 0x1p-16000L;
  39
  40 long double
  41 scalbnl (long double x, int n)
  42 {
  43         union {
  44                 long double e;
  45                 struct ieee_ext bits;
  46         } u;
  47         int k;
  48         u.e = x;
  49         k = u.bits.ext_exp;                     /* extract exponent */
  50         if (k==0) {                             /* 0 or subnormal x */
  51             if ((u.bits.ext_frach
  52 #ifdef EXT_FRACHMBITS
  53                 | u.bits.ext_frachm
  54 #endif /* EXT_FRACHMBITS */
  55 #ifdef EXT_FRACLMBITS
  56                 | u.bits.ext_fraclm
  57 #endif /* EXT_FRACLMBITS */
  58                 | u.bits.ext_fracl)==0) return x;       /* +-0 */
  59             u.e *= 0x1p+128;
  60             k = u.bits.ext_exp - 128;
  61             if (n< -50000) return tiny*x;       /*underflow*/
  62             }
  63         if (k==0x7fff) return x+x;              /* NaN or Inf */
  64         k = k+n;
  65         if (k >= 0x7fff) return huge*copysignl(huge,x); /* overflow  */
  66         if (k > 0)                              /* normal result */
  67             {u.bits.ext_exp = k; return u.e;}
  68         if (k <= -128) {
  69             if (n > 50000)      /* in case integer overflow in n+k */
  70                 return huge*copysign(huge,x);   /*overflow*/
  71             else return tiny*copysign(tiny,x);  /*underflow*/
  72         }
  73         k += 128;                               /* subnormal result */
  74         u.bits.ext_exp = k;
  75         return u.e*0x1p-128;
  76 }
  77
  78 long double
  79 ldexpl(long double x, int n)
  80 {
  81         return scalbnl(x, n);
  82 }