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89c9aa491a
POSIX 2008 states that if the input for 'logb[f|l]' is a subnormal number it should be treated as if it were normalized. This means the implementation should calculate the log2 of the mantissa and add it to the subnormal exponent (-126 for float and -1022 for double and IBM long double). This patch takes care of that.
50 lines
1.4 KiB
C
50 lines
1.4 KiB
C
/* s_logbl.c -- long double version of s_logb.c.
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* Conversion to IEEE quad long double by Jakub Jelinek, jj@ultra.linux.cz.
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*/
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/*
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* ====================================================
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* Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
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*
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* Developed at SunPro, a Sun Microsystems, Inc. business.
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* Permission to use, copy, modify, and distribute this
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* software is freely granted, provided that this notice
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* is preserved.
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* ====================================================
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*/
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/*
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* long double logbl(x)
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* IEEE 754 logb. Included to pass IEEE test suite. Not recommend.
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* Use ilogb instead.
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*/
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#include <math.h>
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#include <math_private.h>
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#include <math_ldbl_opt.h>
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long double
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__logbl (long double x)
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{
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int64_t lx, hx, rhx;
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GET_LDOUBLE_WORDS64 (hx, lx, x);
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hx &= 0x7fffffffffffffffLL; /* high |x| */
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if ((hx | (lx & 0x7fffffffffffffffLL)) == 0)
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return -1.0 / fabs (x);
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if (hx >= 0x7ff0000000000000LL)
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return x * x;
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if (__builtin_expect ((rhx = hx >> 52) == 0, 0))
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{
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/* POSIX specifies that denormal number is treated as
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though it were normalized. */
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int m1 = (hx == 0) ? 0 : __builtin_clzll (hx);
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int m2 = (lx == 0) ? 0 : __builtin_clzll (lx);
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int ma = (m1 == 0) ? m2 + 64 : m1;
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return -1022.0 + (long double)(11 - ma);
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}
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return (long double) (rhx - 1023);
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}
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long_double_symbol (libm, __logbl, logbl);
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