xref: /netbsd-src/external/gpl3/gcc/dist/libquadmath/math/logbq.c (revision 181254a7b1bdde6873432bffef2d2decc4b5c22f)
1*181254a7Smrg /* s_logbl.c -- long double version of s_logb.c.
2*181254a7Smrg  * Conversion to IEEE quad long double by Jakub Jelinek, jj@ultra.linux.cz.
3*181254a7Smrg  */
4*181254a7Smrg 
5*181254a7Smrg /*
6*181254a7Smrg  * ====================================================
7*181254a7Smrg  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
8*181254a7Smrg  *
9*181254a7Smrg  * Developed at SunPro, a Sun Microsystems, Inc. business.
10*181254a7Smrg  * Permission to use, copy, modify, and distribute this
11*181254a7Smrg  * software is freely granted, provided that this notice
12*181254a7Smrg  * is preserved.
13*181254a7Smrg  * ====================================================
14*181254a7Smrg  */
15*181254a7Smrg 
16*181254a7Smrg #if defined(LIBM_SCCS) && !defined(lint)
17*181254a7Smrg static char rcsid[] = "NetBSD: ";
18*181254a7Smrg #endif
19*181254a7Smrg 
20*181254a7Smrg /*
21*181254a7Smrg  * long double logbq(x)
22*181254a7Smrg  * IEEE 754 logb. Included to pass IEEE test suite. Not recommend.
23*181254a7Smrg  * Use ilogb instead.
24*181254a7Smrg  */
25*181254a7Smrg 
26*181254a7Smrg #include "quadmath-imp.h"
27*181254a7Smrg 
28*181254a7Smrg __float128
logbq(__float128 x)29*181254a7Smrg logbq (__float128 x)
30*181254a7Smrg {
31*181254a7Smrg   int64_t lx, hx, ex;
32*181254a7Smrg 
33*181254a7Smrg   GET_FLT128_WORDS64 (hx, lx, x);
34*181254a7Smrg   hx &= 0x7fffffffffffffffLL;	/* high |x| */
35*181254a7Smrg   if ((hx | lx) == 0)
36*181254a7Smrg     return -1.0 / fabsq (x);
37*181254a7Smrg   if (hx >= 0x7fff000000000000LL)
38*181254a7Smrg     return x * x;
39*181254a7Smrg   if ((ex = hx >> 48) == 0)	/* IEEE 754 logb */
40*181254a7Smrg     {
41*181254a7Smrg       /* POSIX specifies that denormal number is treated as
42*181254a7Smrg          though it were normalized.  */
43*181254a7Smrg       int ma;
44*181254a7Smrg       if (hx == 0)
45*181254a7Smrg 	ma = __builtin_clzll (lx) + 64;
46*181254a7Smrg       else
47*181254a7Smrg 	ma = __builtin_clzll (hx);
48*181254a7Smrg       ex -= ma - 16;
49*181254a7Smrg     }
50*181254a7Smrg   return (__float128) (ex - 16383);
51*181254a7Smrg }
52