Currently we hardcode the default NaN value in parts64_default_nan()
using a compile-time ifdef ladder. This is awkward for two cases:
* for single-QEMU-binary we can't hard-code target-specifics like this
* for Arm FEAT_AFP the default NaN value depends on FPCR.AH
(specifically the sign bit is different)
Add a field to float_status to specify the default NaN value; fall
back to the old ifdef behaviour if these are not set.
The default NaN value is specified by setting a uint8_t to a
pattern corresponding to the sign and upper fraction parts of
the NaN; the lower bits of the fraction are set from bit 0 of
the pattern.
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20241202131347.498124-35-peter.maydell@linaro.org
The use_first_nan field in float_status was an xtensa-specific way to
select at runtime from two different NaN propagation rules. Now that
xtensa is using the target-agnostic NaN propagation rule selection
that we've just added, we can remove use_first_nan, because there is
no longer any code that reads it.
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20241202131347.498124-27-peter.maydell@linaro.org
IEEE 758 does not define a fixed rule for which NaN to pick as the
result if both operands of a 3-operand fused multiply-add operation
are NaNs. As a result different architectures have ended up with
different rules for propagating NaNs.
QEMU currently hardcodes the NaN propagation logic into the binary
because pickNaNMulAdd() has an ifdef ladder for different targets.
We want to make the propagation rule instead be selectable at
runtime, because:
* this will let us have multiple targets in one QEMU binary
* the Arm FEAT_AFP architectural feature includes letting
the guest select a NaN propagation rule at runtime
In this commit we add an enum for the propagation rule, the field in
float_status, and the corresponding getters and setters. We change
pickNaNMulAdd to honour this, but because all targets still leave
this field at its default 0 value, the fallback logic will pick the
rule type with the old ifdef ladder.
It's valid not to set a propagation rule if default_nan_mode is
enabled, because in that case there's no need to pick a NaN; all the
callers of pickNaNMulAdd() catch this case and skip calling it.
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20241202131347.498124-16-peter.maydell@linaro.org
IEEE 758 does not define a fixed rule for what NaN to return in
the case of a fused multiply-add of inf * 0 + NaN. Different
architectures thus do different things:
* some return the default NaN
* some return the input NaN
* Arm returns the default NaN if the input NaN is quiet,
and the input NaN if it is signalling
We want to make this logic be runtime selected rather than
hardcoded into the binary, because:
* this will let us have multiple targets in one QEMU binary
* the Arm FEAT_AFP architectural feature includes letting
the guest select a NaN propagation rule at runtime
In this commit we add an enum for the propagation rule, the field in
float_status, and the corresponding getters and setters. We change
pickNaNMulAdd to honour this, but because all targets still leave
this field at its default 0 value, the fallback logic will pick the
rule type with the old ifdef ladder.
Note that four architectures both use the muladd softfloat functions
and did not have a branch of the ifdef ladder to specify their
behaviour (and so were ending up with the "default" case, probably
wrongly): i386, HPPA, SH4 and Tricore. SH4 and Tricore both set
default_nan_mode, and so will never get into pickNaNMulAdd(). For
HPPA and i386 we retain the same behaviour as the old default-case,
which is to not ever return the default NaN. This might not be
correct but it is not a behaviour change.
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20241202131347.498124-4-peter.maydell@linaro.org
IEEE 758 does not define a fixed rule for which NaN to pick as the
result if both operands of a 2-operand operation are NaNs. As a
result different architectures have ended up with different rules for
propagating NaNs.
QEMU currently hardcodes the NaN propagation logic into the binary
because pickNaN() has an ifdef ladder for different targets. We want
to make the propagation rule instead be selectable at runtime,
because:
* this will let us have multiple targets in one QEMU binary
* the Arm FEAT_AFP architectural feature includes letting
the guest select a NaN propagation rule at runtime
* x86 specifies different propagation rules for x87 FPU ops
and for SSE ops, and specifying the rule in the float_status
would let us emulate this, instead of wrongly using the
x87 rules everywhere
In this commit we add an enum for the propagation rule, the field in
float_status, and the corresponding getters and setters. We change
pickNaN to honour this, but because all targets still leave this
field at its default 0 value, the fallback logic will pick the rule
type with the old ifdef ladder.
It's valid not to set a propagation rule if default_nan_mode is
enabled, because in that case there's no need to pick a NaN; all the
callers of pickNaN() catch this case and skip calling it. So we can
already assert that we don't get into the "no rule defined" codepath
for our four targets which always set default_nan_mode: Hexagon,
RiscV, SH4 and Tricore, and for the one target which does not have FP
at all: avr. These targets will not need to be updated to call
set_float_2nan_prop_rule().
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20241025141254.2141506-2-peter.maydell@linaro.org
Cleaned up with scripts/clean-header-guards.pl.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20220506134911.2856099-5-armbru@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Leading underscores followed by a capital letter or underscore are
reserved by the C standard.
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/369
Signed-off-by: Ahmed Abouzied <email@aabouzied.com>
Message-Id: <20210605174938.13782-1-email@aabouzied.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
Use an enumeration instead of raw 32/64/80 values.
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Pass float_status structure pointer to the pickNaN so that
machine-specific settings are available to NaN selection code.
Add use_first_nan property to float_status and use it in Xtensa-specific
pickNaN.
Cc: Peter Maydell <peter.maydell@linaro.org>
Cc: "Alex Bennée" <alex.bennee@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
target/xtensa, the only user of NO_SIGNALING_NANS macro has FPU
implementations with and without the corresponding property. With
NO_SIGNALING_NANS being a macro they cannot be a part of the same QEMU
executable.
Replace macro with new property in float_status to allow cores with
different FPU implementations coexist.
Cc: Peter Maydell <peter.maydell@linaro.org>
Cc: "Alex Bennée" <alex.bennee@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
Give the previously unnamed enum a typedef name. Use the packed
attribute so that we do not affect the layout of the float_status
struct. Use it in the prototypes of relevant functions.
Adjust switch statements as necessary to avoid compiler warnings.
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Slightly tidies the usage within softfloat.c and the
representation in float_status.
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
We have had this on the to-do list for quite some time.
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
There are a bunch of users of the inline helpers who do not need
access to the entire softfloat API. Move those inline helpers into a
new header file which can be included without bringing in the rest of
the world.
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
