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 /*
  17  * long double logbl(x)
  18  * IEEE 754 logb. Included to pass IEEE test suite. Not recommend.
  19  * Use ilogb instead.
  20  */
  21
  22 #include "quadmath-imp.h"
  23
  24 __float128
  25 logbq (__float128 x)
  26 {
  27   int64_t lx, hx, ex;
  28
  29   GET_FLT128_WORDS64 (hx, lx, x);
  30   hx &= 0x7fffffffffffffffLL;   /* high |x| */
  31   if ((hx | lx) == 0)
  32     return -1.0 / fabsq (x);
  33   if (hx >= 0x7fff000000000000LL)
  34     return x * x;
  35   if ((ex = hx >> 48) == 0)     /* IEEE 754 logb */
  36     {
  37       /* POSIX specifies that denormal number is treated as
  38          though it were normalized.  */
  39       int ma;
  40       if (hx == 0)
  41         ma = __builtin_clzll (lx) + 64;
  42       else
  43         ma = __builtin_clzll (hx);
  44       ex -= ma - 16;
  45     }
  46   return (__float128) (ex - 16383);
  47 }