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According to ISO C23 (7.6.4.4), fesetexcept is supposed to set floating-point exception flags without raising a trap (unlike feraiseexcept, which is supposed to raise a trap if feenableexcept was called with the appropriate argument). The flags can be set in the 387 unit or in the SSE unit. When we need to clear a flag, we need to do so in both units, due to the way fetestexcept is implemented. When we need to set a flag, it is sufficient to do it in the SSE unit, because that is guaranteed to not trap. However, on i386 CPUs that have only a 387 unit, set the flags in the 387, as long as this cannot trap. Co-authored-by: Adhemerval Zanella <adhemerval.zanella@linaro.org> Reviewed-by: Carlos O'Donell <carlos@redhat.com>
90 lines
3.0 KiB
C
90 lines
3.0 KiB
C
/* Set floating-point environment exception handling.
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Copyright (C) 1997-2023 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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<https://www.gnu.org/licenses/>. */
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#include <fenv.h>
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#include <ldsodefs.h>
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int
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__fesetexceptflag (const fexcept_t *flagp, int excepts)
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{
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/* The flags can be set in the 387 unit or in the SSE unit. When we need to
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clear a flag, we need to do so in both units, due to the way fetestexcept
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is implemented.
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When we need to set a flag, it is sufficient to do it in the SSE unit,
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because that is guaranteed to not trap. However, on i386 CPUs that have
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only a 387 unit, set the flags in the 387, as long as this cannot trap. */
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fenv_t temp;
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excepts &= FE_ALL_EXCEPT;
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/* Get the current x87 FPU environment. We have to do this since we
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cannot separately set the status word.
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Note: fnstenv masks all floating-point exceptions until the fldenv
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or fldcw below. */
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__asm__ ("fnstenv %0" : "=m" (*&temp));
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if (CPU_FEATURE_USABLE (SSE))
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{
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unsigned int mxcsr;
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/* Clear relevant flags. */
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temp.__status_word &= ~(excepts & ~ *flagp);
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/* Store the new status word (along with the rest of the environment). */
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__asm__ ("fldenv %0" : : "m" (*&temp));
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/* And now similarly for SSE. */
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__asm__ ("stmxcsr %0" : "=m" (*&mxcsr));
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/* Clear or set relevant flags. */
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mxcsr ^= (mxcsr ^ *flagp) & excepts;
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/* Put the new data in effect. */
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__asm__ ("ldmxcsr %0" : : "m" (*&mxcsr));
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}
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else
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{
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/* Clear or set relevant flags. */
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temp.__status_word ^= (temp.__status_word ^ *flagp) & excepts;
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if ((~temp.__control_word) & temp.__status_word & excepts)
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{
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/* Setting the exception flags may trigger a trap (at the next
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floating-point instruction, but that does not matter).
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ISO C 23 § 7.6.4.5 does not allow it. */
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__asm__ volatile ("fldcw %0" : : "m" (*&temp.__control_word));
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return -1;
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}
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/* Store the new status word (along with the rest of the environment). */
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__asm__ ("fldenv %0" : : "m" (*&temp));
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}
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/* Success. */
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return 0;
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}
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#include <shlib-compat.h>
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#if SHLIB_COMPAT (libm, GLIBC_2_1, GLIBC_2_2)
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strong_alias (__fesetexceptflag, __old_fesetexceptflag)
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compat_symbol (libm, __old_fesetexceptflag, fesetexceptflag, GLIBC_2_1);
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#endif
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versioned_symbol (libm, __fesetexceptflag, fesetexceptflag, GLIBC_2_2);
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