sysdeps/ieee754/ldbl-128/s_logbl.c

   1 /* s_logbl.c -- long double version of s_logb.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 #if defined(LIBM_SCCS) && !defined(lint)
  16 static char rcsid[] = "$NetBSD: $";
  17 #endif
  18
  19 /*
  20  * long double logbl(x)
  21  * IEEE 754 logb. Included to pass IEEE test suite. Not recommend.
  22  * Use ilogb instead.
  23  */
  24
  25 #include <math.h>
  26 #include <math_private.h>
  27 #include <libm-alias-ldouble.h>
  28
  29 _Float128
  30 __logbl (_Float128 x)
  31 {
  32   int64_t lx, hx, ex;
  33
  34   GET_LDOUBLE_WORDS64 (hx, lx, x);
  35   hx &= 0x7fffffffffffffffLL;   /* high |x| */
  36   if ((hx | lx) == 0)
  37     return -1.0 / fabsl (x);
  38   if (hx >= 0x7fff000000000000LL)
  39     return x * x;
  40   if ((ex = hx >> 48) == 0)     /* IEEE 754 logb */
  41     {
  42       /* POSIX specifies that denormal number is treated as
  43          though it were normalized.  */
  44       int ma;
  45       if (hx == 0)
  46         ma = __builtin_clzll (lx) + 64;
  47       else
  48         ma = __builtin_clzll (hx);
  49       ex -= ma - 16;
  50     }
  51   return (_Float128) (ex - 16383);
  52 }
  53
  54 libm_alias_ldouble (__logb, logb)