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34e93d6c76
The ldbl-96 implementation of scalblnl (used for x86_64 and ia64) is incorrect for subnormal arguments (this is a separate bug from bug 17803, which is about underflowing results). There are two problems with the adjustments of subnormal arguments: the "two63" variable multiplied by is actually 0x1p52L not 0x1p63L, so is insufficient to make values normal, and then GET_LDOUBLE_EXP(es,x), used to extract the new exponent, extracts it into a variable that isn't used, while the value taken to by the new exponent is wrongly taken from the high part of the mantissa before the adjustment (hx). This patch fixes both those problems and adds appropriate tests. Tested for x86_64. [BZ #17834] * sysdeps/ieee754/ldbl-96/s_scalblnl.c (two63): Change value to 0x1p63L. (__scalblnl): Get new exponent of adjusted subnormal value from ES not HX. * math/libm-test.inc (scalbn_test_data): Add more tests. (scalbln_test_data): Likewise.
61 lines
1.8 KiB
C
61 lines
1.8 KiB
C
/* s_scalbnl.c -- long double version of s_scalbn.c.
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* Conversion to long double by Ulrich Drepper,
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* Cygnus Support, drepper@cygnus.com.
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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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* scalbnl (long double x, int n)
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* scalbnl(x,n) returns x* 2**n computed by exponent
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* manipulation rather than by actually performing an
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* exponentiation or a multiplication.
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*/
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#include <math.h>
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#include <math_private.h>
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static const long double
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two63 = 0x1p63L,
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twom63 = 1.08420217248550443400e-19,
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huge = 1.0e+4900L,
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tiny = 1.0e-4900L;
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long double
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__scalblnl (long double x, long int n)
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{
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int32_t k,es,hx,lx;
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GET_LDOUBLE_WORDS(es,hx,lx,x);
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k = es&0x7fff; /* extract exponent */
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if (__builtin_expect(k==0, 0)) { /* 0 or subnormal x */
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if ((lx|(hx&0x7fffffff))==0) return x; /* +-0 */
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x *= two63;
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GET_LDOUBLE_EXP(es,x);
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k = (es&0x7fff) - 63;
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}
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if (__builtin_expect(k==0x7fff, 0)) return x+x; /* NaN or Inf */
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if (__builtin_expect(n< -50000, 0))
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return tiny*__copysignl(tiny,x);
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if (__builtin_expect(n> 50000 || k+n > 0x7ffe, 0))
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return huge*__copysignl(huge,x); /* overflow */
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/* Now k and n are bounded we know that k = k+n does not
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overflow. */
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k = k+n;
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if (__builtin_expect(k > 0, 1)) /* normal result */
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{SET_LDOUBLE_EXP(x,(es&0x8000)|k); return x;}
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if (k <= -63)
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return tiny*__copysignl(tiny,x); /*underflow*/
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k += 63; /* subnormal result */
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SET_LDOUBLE_EXP(x,(es&0x8000)|k);
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return x*twom63;
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}
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