| 1 | /* s_logbl.c -- long double version of s_logb.c. |
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| 2 | */ |
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| 3 | |
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| 4 | /* |
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| 5 | * ==================================================== |
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| 6 | * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. |
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| 7 | * |
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| 8 | * Developed at SunPro, a Sun Microsystems, Inc. business. |
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| 9 | * Permission to use, copy, modify, and distribute this |
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| 10 | * software is freely granted, provided that this notice |
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| 11 | * is preserved. |
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| 12 | * ==================================================== |
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| 13 | */ |
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| 14 | |
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| 15 | #if defined(LIBM_SCCS) && !defined(lint) |
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| 16 | static char rcsid[] = "$NetBSD: $" ; |
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| 17 | #endif |
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| 18 | |
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| 19 | /* |
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| 20 | * long double logbl(x) |
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| 21 | * IEEE 754 logb. Included to pass IEEE test suite. Not recommend. |
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| 22 | * Use ilogb instead. |
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| 23 | */ |
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| 24 | |
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| 25 | #include <math.h> |
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| 26 | #include <math_private.h> |
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| 27 | #include <libm-alias-ldouble.h> |
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| 28 | |
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| 29 | _Float128 |
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| 30 | __logbl (_Float128 x) |
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| 31 | { |
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| 32 | int64_t lx, hx, ex; |
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| 33 | |
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| 34 | GET_LDOUBLE_WORDS64 (hx, lx, x); |
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| 35 | hx &= 0x7fffffffffffffffLL; /* high |x| */ |
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| 36 | if ((hx | lx) == 0) |
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| 37 | return -1.0 / fabsl (x); |
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| 38 | if (hx >= 0x7fff000000000000LL) |
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| 39 | return x * x; |
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| 40 | if ((ex = hx >> 48) == 0) /* IEEE 754 logb */ |
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| 41 | { |
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| 42 | /* POSIX specifies that denormal number is treated as |
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| 43 | though it were normalized. */ |
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| 44 | int ma; |
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| 45 | if (hx == 0) |
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| 46 | ma = __builtin_clzll (lx) + 64; |
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| 47 | else |
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| 48 | ma = __builtin_clzll (hx); |
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| 49 | ex -= ma - 16; |
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| 50 | } |
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| 51 | return (_Float128) (ex - 16383); |
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| 52 | } |
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| 53 | |
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| 54 | libm_alias_ldouble (__logb, logb) |
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| 55 | |
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