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524ae9ea2e
The ldbl-128ibm implementation of ilogbl 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, ilogbl (0x1.ffffffffffffffp1L) returns 2 but should return 1. (This is similar to (fixed) bug 16740 for frexpl, and bug 18030 for logbl.) This patch adds checks for that case. Tested for powerpc. [BZ #18029] * sysdeps/ieee754/ldbl-128ibm/e_ilogbl.c (__ieee754_ilogbl): Adjust exponent of power of 2 down when low part has opposite sign. * math/libm-test.inc (ilogb_test_data): Add more tests.
71 lines
1.8 KiB
C
71 lines
1.8 KiB
C
/* s_ilogbl.c -- long double version of s_ilogb.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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#if defined(LIBM_SCCS) && !defined(lint)
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static char rcsid[] = "$NetBSD: $";
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#endif
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/* ilogbl(long double x)
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* return the binary exponent of non-zero x
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* ilogbl(0) = FP_ILOGB0
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* ilogbl(NaN) = FP_ILOGBNAN (no signal is raised)
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* ilogbl(+-Inf) = INT_MAX (no signal is raised)
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*/
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#include <limits.h>
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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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int __ieee754_ilogbl(long double x)
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{
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int64_t hx, hxs;
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int ix;
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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;
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if(hx <= 0x0010000000000000LL) {
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if(hx==0)
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return FP_ILOGB0; /* ilogbl(0) = FP_ILOGB0 */
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else /* subnormal x */
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for (ix = -1022, hx<<=11; hx>0; hx<<=1) ix -=1;
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return ix;
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}
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else if (hx < 0x7ff0000000000000LL)
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{
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int hexp = (hx >> 52) - 0x3ff;
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/* If the high part is a power of 2, and the low part is
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nonzero with the opposite sign, the low part affects
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the exponent. */
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if ((hx & 0x000fffffffffffffLL) == 0)
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{
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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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hexp--;
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}
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return hexp;
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}
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else if (FP_ILOGBNAN != INT_MAX) {
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/* ISO C99 requires ilogbl(+-Inf) == INT_MAX. */
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if (hx==0x7ff0000000000000LL)
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return INT_MAX;
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}
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return FP_ILOGBNAN;
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}
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