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b72ca61b71
Reserved bits in the Floating-Point Control and Status Register (FCSR) should not be implicitly cleared by fedisableexcept or feenableexcept, there is no reason to. Among these are the 8 condition codes and one of the two bits reserved for architecture implementers (bits #22 & #21). As to the latter, there is no reason to treat any of them as reserved either, they should be user controllable and settable via __fpu_control override as the user sees fit. For example in processors implemented by MIPS Technologies, such as the 5Kf or the 24Kf, these bits are used to change the treatment of denormalised operands and tiny results: bit #22 is Flush Override (FO) and bit #21 is Flush to Nearest (FN). They cause non-IEEE-compliant behaviour, but some programs may have a use for such modes of operation; the library should not obstruct such use just as it does not for the architectural Flush to Zero (FS) bit (bit #24). Therefore the change adjusts the reserved mask accordingly and also documents the distinction between bits 22:21 and 20:18.
41 lines
1.2 KiB
C
41 lines
1.2 KiB
C
/* Disable floating-point exceptions.
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Copyright (C) 2000-2013 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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Contributed by Andreas Jaeger <aj@suse.de>, 2000.
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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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#include <fenv.h>
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#include <fenv_libc.h>
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#include <fpu_control.h>
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int
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fedisableexcept (int excepts)
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{
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unsigned int new_exc, old_exc;
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/* Get the current control word. */
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_FPU_GETCW (new_exc);
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old_exc = (new_exc & ENABLE_MASK) >> ENABLE_SHIFT;
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excepts &= FE_ALL_EXCEPT;
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new_exc &= ~(excepts << ENABLE_SHIFT);
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_FPU_SETCW (new_exc);
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return old_exc;
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}
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