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The ldbl-128ibm implementation of nearbyintl uses logic that only works in round-to-nearest mode. This contrasts with rintl, which works in all rounding modes. Now, arguably nearbyintl could simply be aliased to rintl, given that spurious "inexact" is generally allowed for ldbl-128ibm, even for the underlying arithmetic operations. But given that the only point of nearbyintl is to avoid "inexact", this patch follows the more conservative approach of adding conditionals to the rintl implementation to make it suitable for use to implement nearbyintl, then builds it for nearbyintl with USE_AS_NEARBYINTL defined. The test test-nearbyint-except-2 shows up issues when traps on "inexact" are enabled, which turn out to be problems with the powerpc fenv_private.h implementation (two functions that should disable exception traps potentially failing to do so in some cases); this patch duly fixes that as well (I don't see any other existing cases where this would be user-visible; there isn't much use of *_NOEX, *hold* etc. in libm that requires exceptions to be discarded and not trapped on). Tested for powerpc. [BZ #19790] * sysdeps/ieee754/ldbl-128ibm/s_rintl.c [USE_AS_NEARBYINTL] (rintl): Define as macro. [USE_AS_NEARBYINTL] (__rintl): Likewise. (__rintl) [USE_AS_NEARBYINTL]: Use SET_RESTORE_ROUND_NOEX instead of fesetround. Ensure results are evaluated before end of scope. * sysdeps/ieee754/ldbl-128ibm/s_nearbyintl.c: Define USE_AS_NEARBYINTL and include s_rintl.c. * sysdeps/powerpc/fpu/fenv_private.h (libc_feholdsetround_ppc): Disable exception traps in new environment. (libc_feholdsetround_ppc_ctx): Likewise.
127 lines
3.4 KiB
C
127 lines
3.4 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) 2006-2016 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 <fenv.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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#ifdef USE_AS_NEARBYINTL
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# define rintl nearbyintl
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# define __rintl __nearbyintl
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#endif
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long double
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__rintl (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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int save_round = fegetround ();
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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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#ifdef USE_AS_NEARBYINTL
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SET_RESTORE_ROUND_NOEX (FE_TONEAREST);
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#else
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fesetround (FE_TONEAREST);
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#endif
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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. If the low double
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happens to be exactly 0.5 or -0.5, you might think that this
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subtraction could result in an incorrect conversion. For
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instance, subtracting an odd number would cause this function
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to round in the wrong direction. However, if we have a
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canonical long double with the low double 0.5 or -0.5, then the
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high double must be even. */
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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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xh -= lo;
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ldbl_canonicalize (&xh, &xl);
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switch (save_round)
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{
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case FE_TONEAREST:
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if (xl > 0.0 && xh == 0.5)
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lo += 1.0;
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else if (xl < 0.0 && -xh == 0.5)
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lo -= 1.0;
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break;
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case FE_TOWARDZERO:
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if (orig_xh < 0.0)
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goto do_up;
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/* Fall thru */
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case FE_DOWNWARD:
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if (xh < 0.0 || (xh == 0.0 && xl < 0.0))
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lo -= 1.0;
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break;
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case FE_UPWARD:
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do_up:
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if (xh > 0.0 || (xh == 0.0 && xl > 0.0))
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lo += 1.0;
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break;
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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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/* Ensure we return -0 rather than +0 when appropriate. */
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if (orig_xh < 0.0)
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xh = -__builtin_fabs (xh);
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#ifdef USE_AS_NEARBYINTL
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math_force_eval (xh);
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math_force_eval (xl);
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#else
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fesetround (save_round);
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#endif
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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, __rintl, rintl);
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