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The ldbl-128ibm implementation of logbl produces incorrect results when the high part of the argument is a power of 2 and the low part a nonzero number with the opposite sign (and so the returned exponent should be 1 less than that of the high part). For example, logbl (0x1.ffffffffffffffp1L) returns 2 but should return 1. (This is similar to (fixed) bug 16740 for frexpl, and (fixed) bug 18029 for ilogbl.) This patch adds checks for that case. Tested for powerpc. [BZ #18030] * sysdeps/ieee754/ldbl-128ibm/s_logbl.c (__logbl): Adjust exponent of power of 2 down when low part has opposite sign. * math/libm-test.inc (logb_test_data): Add more tests.
61 lines
1.6 KiB
C
61 lines
1.6 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 hx, hxs, rhx;
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double xhi, xlo;
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ldbl_unpack (x, &xhi, &xlo);
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EXTRACT_WORDS64 (hx, xhi);
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hxs = hx;
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hx &= 0x7fffffffffffffffLL; /* high |x| */
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if (hx == 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 (__glibc_unlikely ((rhx = hx >> 52) == 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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rhx -= __builtin_clzll (hx) - 12;
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}
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else if ((hx & 0x000fffffffffffffLL) == 0)
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{
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/* If the high part is a power of 2, and the low part is nonzero
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with the opposite sign, the low part affects the
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exponent. */
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int64_t lx;
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EXTRACT_WORDS64 (lx, xlo);
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if ((hxs ^ lx) < 0 && (lx & 0x7fffffffffffffffLL) != 0)
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rhx--;
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}
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return (long double) (rhx - 1023);
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}
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#ifndef __logbl
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long_double_symbol (libm, __logbl, logbl);
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#endif
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