405849610f
The underflow exception cases were wrong.
This is one weird area of ieee1754 handling in that the underflow
behavior changes based upon whether underflow is enabled in the trap
enable mask of the FPU control register. As a specific case the Sparc
V9 manual gives us the following description:
--------------------
If UFM = 0: Underflow occurs if a nonzero result is tiny and a
loss of accuracy occurs. Tininess may be detected
before or after rounding. Loss of accuracy may be
either a denormalization loss or an inexact result.
If UFM = 1: Underflow occurs if a nonzero result is tiny.
Tininess may be detected before or after rounding.
--------------------
What this amounts to in the packing case is if we go subnormal,
we set underflow if any of the following are true:
1) rounding sets inexact
2) we ended up rounding back up to normal (this is the case where
we set the exponent to 1 and set the fraction to zero), this
should set inexact too
3) underflow is set in FPU control register trap-enable mask
The initially discovered example was "DBL_MIN / 16.0" which
incorrectly generated an underflow. It should not, unless underflow
is set in the trap-enable mask of the FPU csr.
Another example, "0x0.0000000000001p-1022 / 16.0", should signal both
inexact and underflow. The cpu implementations and ieee1754
literature is very clear about this. This is case #2 above.
However, if underflow is set in the trap enable mask, only underflow
should be set and reported as a trap. That is handled properly by the
prioritization logic in
arch/sparc{,64}/math-emu/math.c:record_exception().
Based upon a report and test case from Jakub Jelinek.
Signed-off-by: David S. Miller <davem@davemloft.net>
189 lines
4.7 KiB
C
189 lines
4.7 KiB
C
/* Software floating-point emulation.
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Copyright (C) 1997,1998,1999 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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Contributed by Richard Henderson (rth@cygnus.com),
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Jakub Jelinek (jj@ultra.linux.cz),
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David S. Miller (davem@redhat.com) and
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Peter Maydell (pmaydell@chiark.greenend.org.uk).
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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 Library General Public License as
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published by the Free Software Foundation; either version 2 of the
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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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Library General Public License for more details.
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You should have received a copy of the GNU Library General Public
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License along with the GNU C Library; see the file COPYING.LIB. If
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not, write to the Free Software Foundation, Inc.,
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59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. */
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#ifndef __MATH_EMU_SOFT_FP_H__
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#define __MATH_EMU_SOFT_FP_H__
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#include <asm/sfp-machine.h>
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/* Allow sfp-machine to have its own byte order definitions. */
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#ifndef __BYTE_ORDER
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#include <endian.h>
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#endif
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#define _FP_WORKBITS 3
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#define _FP_WORK_LSB ((_FP_W_TYPE)1 << 3)
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#define _FP_WORK_ROUND ((_FP_W_TYPE)1 << 2)
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#define _FP_WORK_GUARD ((_FP_W_TYPE)1 << 1)
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#define _FP_WORK_STICKY ((_FP_W_TYPE)1 << 0)
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#ifndef FP_RND_NEAREST
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# define FP_RND_NEAREST 0
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# define FP_RND_ZERO 1
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# define FP_RND_PINF 2
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# define FP_RND_MINF 3
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#ifndef FP_ROUNDMODE
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# define FP_ROUNDMODE FP_RND_NEAREST
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#endif
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#endif
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/* By default don't care about exceptions. */
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#ifndef FP_EX_INVALID
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#define FP_EX_INVALID 0
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#endif
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#ifndef FP_EX_OVERFLOW
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#define FP_EX_OVERFLOW 0
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#endif
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#ifndef FP_EX_UNDERFLOW
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#define FP_EX_UNDERFLOW
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#endif
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#ifndef FP_EX_DIVZERO
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#define FP_EX_DIVZERO 0
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#endif
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#ifndef FP_EX_INEXACT
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#define FP_EX_INEXACT 0
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#endif
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#ifndef FP_EX_DENORM
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#define FP_EX_DENORM 0
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#endif
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#ifdef _FP_DECL_EX
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#define FP_DECL_EX \
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int _fex = 0; \
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_FP_DECL_EX
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#else
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#define FP_DECL_EX int _fex = 0
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#endif
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#ifndef FP_INIT_ROUNDMODE
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#define FP_INIT_ROUNDMODE do {} while (0)
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#endif
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#ifndef FP_HANDLE_EXCEPTIONS
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#define FP_HANDLE_EXCEPTIONS do {} while (0)
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#endif
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/* By default we never flush denormal input operands to signed zero. */
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#ifndef FP_DENORM_ZERO
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#define FP_DENORM_ZERO 0
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#endif
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#ifndef FP_INHIBIT_RESULTS
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/* By default we write the results always.
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* sfp-machine may override this and e.g.
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* check if some exceptions are unmasked
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* and inhibit it in such a case.
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*/
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#define FP_INHIBIT_RESULTS 0
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#endif
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#ifndef FP_TRAPPING_EXCEPTIONS
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#define FP_TRAPPING_EXCPETIONS 0
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#endif
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#define FP_SET_EXCEPTION(ex) \
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_fex |= (ex)
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#define FP_UNSET_EXCEPTION(ex) \
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_fex &= ~(ex)
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#define FP_CUR_EXCEPTIONS \
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(_fex)
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#define FP_CLEAR_EXCEPTIONS \
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_fex = 0
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#define _FP_ROUND_NEAREST(wc, X) \
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do { \
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if ((_FP_FRAC_LOW_##wc(X) & 15) != _FP_WORK_ROUND) \
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_FP_FRAC_ADDI_##wc(X, _FP_WORK_ROUND); \
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} while (0)
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#define _FP_ROUND_ZERO(wc, X) 0
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#define _FP_ROUND_PINF(wc, X) \
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do { \
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if (!X##_s && (_FP_FRAC_LOW_##wc(X) & 7)) \
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_FP_FRAC_ADDI_##wc(X, _FP_WORK_LSB); \
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} while (0)
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#define _FP_ROUND_MINF(wc, X) \
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do { \
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if (X##_s && (_FP_FRAC_LOW_##wc(X) & 7)) \
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_FP_FRAC_ADDI_##wc(X, _FP_WORK_LSB); \
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} while (0)
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#define _FP_ROUND(wc, X) \
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do { \
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if (_FP_FRAC_LOW_##wc(X) & 7) \
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FP_SET_EXCEPTION(FP_EX_INEXACT); \
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switch (FP_ROUNDMODE) \
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{ \
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case FP_RND_NEAREST: \
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_FP_ROUND_NEAREST(wc,X); \
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break; \
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case FP_RND_ZERO: \
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_FP_ROUND_ZERO(wc,X); \
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break; \
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case FP_RND_PINF: \
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_FP_ROUND_PINF(wc,X); \
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break; \
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case FP_RND_MINF: \
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_FP_ROUND_MINF(wc,X); \
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break; \
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} \
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} while (0)
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#define FP_CLS_NORMAL 0
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#define FP_CLS_ZERO 1
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#define FP_CLS_INF 2
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#define FP_CLS_NAN 3
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#define _FP_CLS_COMBINE(x,y) (((x) << 2) | (y))
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#include <math-emu/op-1.h>
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#include <math-emu/op-2.h>
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#include <math-emu/op-4.h>
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#include <math-emu/op-8.h>
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#include <math-emu/op-common.h>
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/* Sigh. Silly things longlong.h needs. */
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#define UWtype _FP_W_TYPE
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#define W_TYPE_SIZE _FP_W_TYPE_SIZE
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typedef int SItype __attribute__((mode(SI)));
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typedef int DItype __attribute__((mode(DI)));
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typedef unsigned int USItype __attribute__((mode(SI)));
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typedef unsigned int UDItype __attribute__((mode(DI)));
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#if _FP_W_TYPE_SIZE == 32
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typedef unsigned int UHWtype __attribute__((mode(HI)));
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#elif _FP_W_TYPE_SIZE == 64
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typedef USItype UHWtype;
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#endif
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#ifndef umul_ppmm
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#include <stdlib/longlong.h>
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#endif
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#endif /* __MATH_EMU_SOFT_FP_H__ */
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