Introduce a separate control from float_snan_rule
that applies only to the OCP E4M3 format.
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Move get_float_default_nan_pattern to softfloat-specialize.c.inc,
since there are no external users.
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Drop FloatFTZDetection and use #defines, like we do for
tininess_before_rounding. Rename get_float_ftz_detection
to get_ftz_before_rounding and move to softfloat.c, as
there are no external users.
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Rename get_float_detect_tininess to get_tininess_before_rounding
and move to softfloat.c, as there are no external users.
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Unify handling of the two snan parameters, letting the
caller simply extract the msb.
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Tested-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Currently we have a compile-time shortcut where we return a hardcode
value from snan_bit_is_one() on everything except MIPS, because we
know that's the only target that needs to change
status->no_signaling_nans at runtime.
Remove the ifdef, so we always look at the status flag. This means
we must update the two targets (HPPA and SH4) that were previously
hardcoded to return true so that they set the status flag correctly.
This has no behavioural change, but will be necessary if we want to
build softfloat once for all targets.
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20250224111524.1101196-11-peter.maydell@linaro.org
Message-id: 20250217125055.160887-9-peter.maydell@linaro.org
In Intel terminology, a floatx80 Infinity with the explicit integer
bit clear is a "pseudo-infinity"; for x86 these are not valid
infinity values. m68k is looser and does not care whether the
Integer bit is set or clear in an infinity.
Move this setting to runtime rather than using an ifdef in
floatx80_is_infinity().
Since this was the last use of the floatx80_infinity global constant,
we remove it and its definition here.
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-id: 20250224111524.1101196-6-peter.maydell@linaro.org
Message-id: 20250217125055.160887-5-peter.maydell@linaro.org
Currently we hardcode at compile time whether the floatx80 default
Infinity value has the explicit integer bit set or not (x86 sets it;
m68k does not). To be able to compile softfloat once for all targets
we'd like to move this setting to runtime.
Define a new FloatX80Behaviour enum which is a set of flags that
define the target's floatx80 handling. Initially we define just one
flag, for whether the default Infinity has the Integer bit set or
not, but we will expand this in future commits to cover the other
floatx80 target specifics that we currently make compile-time
settings.
Define a new function floatx80_default_inf() which returns the
appropriate default Infinity value of the given sign, and use it in
the code that was previously directly using the compile-time constant
floatx80_infinity_{low,high} values when packing an infinity into a
floatx80.
Since floatx80 is highly unlikely to be supported in any new
architecture, and the existing code is generally written as "default
to like x87, with an ifdef for m68k", we make the default value for
the floatx80 behaviour flags be "what x87 does". This means we only
need to change the m68k target to specify the behaviour flags.
(Other users of floatx80 are the Arm NWFPE emulation, which is
obsolete and probably not actually doing the right thing anyway, and
the PPC xsrqpxp insn. Making the default be "like x87" avoids our
needing to review and test for behaviour changes there.)
We will clean up the remaining uses of the floatx80_infinity global
constant in subsequent commits.
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-id: 20250224111524.1101196-2-peter.maydell@linaro.org
Message-id: 20250217125055.160887-2-peter.maydell@linaro.org
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
We create our 128-bit default NaN by calling parts64_default_nan()
and then adjusting the result. We can do the same trick for creating
the floatx80 default NaN, which lets us drop a target ifdef.
floatx80 is used only by:
i386
m68k
arm nwfpe old floating-point emulation emulation support
(which is essentially dead, especially the parts involving floatx80)
PPC (only in the xsrqpxp instruction, which just rounds an input
value by converting to floatx80 and back, so will never generate
the default NaN)
The floatx80 default NaN as currently implemented is:
m68k: sign = 0, exp = 1...1, int = 1, frac = 1....1
i386: sign = 1, exp = 1...1, int = 1, frac = 10...0
These are the same as the parts64_default_nan for these architectures.
This is technically a possible behaviour change for arm linux-user
nwfpe emulation emulation, because the default NaN will now have the
sign bit clear. But we were already generating a different floatx80
default NaN from the real kernel emulation we are supposedly
following, which appears to use an all-bits-1 value:
https://elixir.bootlin.com/linux/v6.12/source/arch/arm/nwfpe/softfloat-specialize#L267
This won't affect the only "real" use of the nwfpe emulation, which
is ancient binaries that used it as part of the old floating point
calling convention; that only uses loads and stores of 32 and 64 bit
floats, not any of the floatx80 behaviour the original hardware had.
We also get the nwfpe float64 default NaN value wrong:
https://elixir.bootlin.com/linux/v6.12/source/arch/arm/nwfpe/softfloat-specialize#L166
so if we ever cared about this obscure corner the right fix would be
to correct that so nwfpe used its own default-NaN setting rather
than the Arm VFP one.
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20241202131347.498124-29-peter.maydell@linaro.org
Set the Float3NaNPropRule explicitly for HPPA, and remove the
ifdef from pickNaNMulAdd().
HPPA is the only target that was using the default branch of the
ifdef ladder (other targets either do not use muladd or set
default_nan_mode), so we can remove the ifdef fallback entirely now
(allowing the "rule not set" case to fall into the default of the
switch statement and assert).
We add a TODO note that the HPPA rule is probably wrong; this is
not a behavioural change for this refactoring.
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20241202131347.498124-26-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
The new implementation of pickNaNMulAdd() will find it convenient
to know whether at least one of the three arguments to the muladd
was a signaling NaN. We already calculate that in the caller,
so pass it in as a new bool have_snan.
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20241202131347.498124-15-peter.maydell@linaro.org
Set the FloatInfZeroNaNRule explicitly for the HPPA target,
so we can remove the ifdef from pickNaNMulAdd().
As this is the last target to be converted to explicitly setting
the rule, we can remove the fallback code in pickNaNMulAdd()
entirely.
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20241202131347.498124-14-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
If the target sets default_nan_mode then we're always going to return
the default NaN, and pickNaNMulAdd() no longer has any side effects.
For consistency with pickNaN(), check for default_nan_mode before
calling pickNaNMulAdd().
When we convert pickNaNMulAdd() to allow runtime selection of the NaN
propagation rule, this means we won't have to make the targets which
use default_nan_mode also set a propagation rule.
Since RiscV always uses default_nan_mode, this allows us to remove
its ifdef case from pickNaNMulAdd().
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20241202131347.498124-3-peter.maydell@linaro.org
