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87 lines
2.5 KiB
C
87 lines
2.5 KiB
C
/* Round to int long double floating-point values.
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IBM extended format long double version.
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Copyright (C) 2006, 2007, 2012 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<http://www.gnu.org/licenses/>. */
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/* This has been coded in assembler because GCC makes such a mess of it
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when it's coded in C. */
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#include <math.h>
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#include <math_ldbl_opt.h>
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#include <float.h>
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#include <ieee754.h>
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long double
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__roundl (long double x)
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{
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double xh, xl, hi, lo;
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ldbl_unpack (x, &xh, &xl);
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/* Return Inf, Nan, +/-0 unchanged. */
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if (__builtin_expect (xh != 0.0
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&& __builtin_isless (__builtin_fabs (xh),
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__builtin_inf ()), 1))
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{
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double orig_xh;
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/* Long double arithmetic, including the canonicalisation below,
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only works in round-to-nearest mode. */
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/* Convert the high double to integer. */
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orig_xh = xh;
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hi = ldbl_nearbyint (xh);
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/* Subtract integral high part from the value. */
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xh -= hi;
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ldbl_canonicalize (&xh, &xl);
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/* Now convert the low double, adjusted for any remainder from the
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high double. */
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lo = ldbl_nearbyint (xh);
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/* Adjust the result when the remainder is exactly 0.5. nearbyint
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rounds values halfway between integers to the nearest even
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integer. roundl must round away from zero.
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Also correct cases where nearbyint returns an incorrect value
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for LO. */
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xh -= lo;
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ldbl_canonicalize (&xh, &xl);
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if (xh == 0.5)
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{
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if (xl > 0.0 || (xl == 0.0 && orig_xh > 0.0))
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lo += 1.0;
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}
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else if (-xh == 0.5)
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{
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if (xl < 0.0 || (xl == 0.0 && orig_xh < 0.0))
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lo -= 1.0;
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}
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/* Ensure the final value is canonical. In certain cases,
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rounding causes hi,lo calculated so far to be non-canonical. */
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xh = hi;
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xl = lo;
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ldbl_canonicalize (&xh, &xl);
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}
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return ldbl_pack (xh, xl);
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}
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long_double_symbol (libm, __roundl, roundl);
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