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git.ipfire.org Git - thirdparty/glibc.git/blob - sysdeps/powerpc/power7/fpu/s_logbl.c
1 /* logbl(). PowerPC/POWER7 version.
2 Copyright (C) 2012-2019 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
5 The GNU C Library is free software; you can redistribute it and/or
6 modify it under the terms of the GNU Lesser General Public
7 License as published by the Free Software Foundation; either
8 version 2.1 of the License, or (at your option) any later version.
10 The GNU C Library is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 Lesser General Public License for more details.
15 You should have received a copy of the GNU Lesser General Public
16 License along with the GNU C Library; if not, see
17 <http://www.gnu.org/licenses/>. */
20 #include <math_private.h>
21 #include <math_ldbl_opt.h>
23 /* This implementation avoids FP to INT conversions by using VSX
24 bitwise instructions over FP values. */
26 static const double two1div52
= 2.220446049250313e-16; /* 1/2**52 */
27 static const double two10m1
= -1023.0; /* 2**10 -1 */
29 /* FP mask to extract the exponent. */
31 unsigned long long mask
;
33 } mask
= { 0x7ff0000000000000ULL
};
36 __logbl (long double x
)
42 if (__builtin_expect (x
== 0.0L, 0))
43 /* Raise FE_DIVBYZERO and return -HUGE_VAL[LF]. */
44 return -1.0L / __builtin_fabsl (x
);
46 ldbl_unpack (x
, &xh
, &xl
);
47 EXTRACT_WORDS64 (hx
, xh
);
48 /* ret = x & 0x7ff0000000000000; */
50 "xxland %x0,%x1,%x2\n"
53 : "f" (xh
), "f" (mask
.d
));
54 /* ret = (ret >> 52) - 1023.0; */
55 ret
= (ret
* two1div52
) + two10m1
;
56 if (__builtin_expect (ret
> -two10m1
, 0))
57 /* Multiplication is used to set logb (+-INF) = INF. */
59 else if (__builtin_expect (ret
== two10m1
, 0))
61 /* POSIX specifies that denormal number is treated as
62 though it were normalized. */
63 return (long double) (- (__builtin_clzll (hx
& 0x7fffffffffffffffLL
) \
66 else if ((hx
& 0x000fffffffffffffLL
) == 0)
68 /* If the high part is a power of 2, and the low part is nonzero
69 with the opposite sign, the low part affects the
72 EXTRACT_WORDS64 (lx
, xl
);
73 rhx
= (hx
& 0x7ff0000000000000LL
) >> 52;
74 if ((hx
^ lx
) < 0 && (lx
& 0x7fffffffffffffffLL
) != 0)
76 return (long double) (rhx
- 1023);
78 /* Test to avoid logb_downward (0.0) == -0.0. */
79 return ret
== -0.0 ? 0.0 : ret
;
82 long_double_symbol (libm
, __logbl
, logbl
);