libquadmath/math/logbq.c

   1 /* s_logbl.c -- long double version of s_logb.c.
   2  * Conversion to IEEE quad long double by Jakub Jelinek, jj@ultra.linux.cz.
   3  */
   4
   5 /*
   6  * ====================================================
   7  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
   8  *
   9  * Developed at SunPro, a Sun Microsystems, Inc. business.
  10  * Permission to use, copy, modify, and distribute this
  11  * software is freely granted, provided that this notice
  12  * is preserved.
  13  * ====================================================
  14  */
  15
  16 #if defined(LIBM_SCCS) && !defined(lint)
  17 static char rcsid[] = "$NetBSD: $";
  18 #endif
  19
  20 /*
  21  * long double logbq(x)
  22  * IEEE 754 logb. Included to pass IEEE test suite. Not recommend.
  23  * Use ilogb instead.
  24  */
  25
  26 #include "quadmath-imp.h"
  27
  28 __float128
  29 logbq (__float128 x)
  30 {
  31   int64_t lx, hx, ex;
  32
  33   GET_FLT128_WORDS64 (hx, lx, x);
  34   hx &= 0x7fffffffffffffffLL;   /* high |x| */
  35   if ((hx | lx) == 0)
  36     return -1.0 / fabsq (x);
  37   if (hx >= 0x7fff000000000000LL)
  38     return x * x;
  39   if ((ex = hx >> 48) == 0)     /* IEEE 754 logb */
  40     {
  41       /* POSIX specifies that denormal number is treated as
  42          though it were normalized.  */
  43       int ma;
  44       if (hx == 0)
  45         ma = __builtin_clzll (lx) + 64;
  46       else
  47         ma = __builtin_clzll (hx);
  48       ex -= ma - 16;
  49     }
  50   return (__float128) (ex - 16383);
  51 }