Changing the sign before rounding affects the correctness of
the asymmetric rouding modes: float_round_up and float_round_down.
Reported-by: WANG Rui <wangrui@loongson.cn>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Now we have removed all the target-specifics from the softfloat code,
we can switch to building it once for the whole system rather than
once per target.
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Tested-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20250224111524.1101196-13-peter.maydell@linaro.org
Message-id: 20250217125055.160887-11-peter.maydell@linaro.org
We happen to know that for the PPC target the FP status flags (and in
particular float_flag_inexact) will always be cleared before a
floating point operation, and so can_use_fpu() will always return
false. So we speed things up a little by forcing QEMU_NO_HARDFLOAT
to true on that target.
We would like to build softfloat once for all targets; that means
removing target-specific ifdefs. Remove the check for TARGET_PPC;
this won't change behaviour because can_use_fpu() will see that
float_flag_inexact is clear and take the softfloat path anyway.
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20250224111524.1101196-12-peter.maydell@linaro.org
Message-id: 20250217125055.160887-10-peter.maydell@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
Currently we have a compile-time shortcut where we
return false from no_signaling_nans() on everything except
Xtensa, because we know that's the only target that
might ever set status->no_signaling_nans.
Remove the ifdef, so we always look at the status flag;
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: 20250224111524.1101196-10-peter.maydell@linaro.org
Message-id: 20250217125055.160887-8-peter.maydell@linaro.org
Currently we compile-time set an 'm68k_denormal' flag in the FloatFmt
for floatx80 for m68k. This controls our handling of what the Intel
documentation calls a "pseudo-denormal": a value where the exponent
field is zero and the explicit integer bit is set.
For x86, the x87 FPU is supposed to accept a pseudo-denormal as
input, but never generate one on output. For m68k, these values are
permitted on input and may be produced on output.
Replace the flag in the FloatFmt with a flag indicating whether the
float format has an explicit bit (which will be true for floatx80 for
all targets, and false for every other float type). Then we can gate
the handling of these pseudo-denormals on the setting of a
floatx80_behaviour flag.
As far as I can see from the code we don't actually handle the
x86-mandated "accept on input but don't generate" behaviour, because
the handling in partsN(canonicalize) looked at fmt->m68k_denormal.
So I have added TODO comments to that effect.
This commit doesn't change any behaviour for any target.
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: 20250224111524.1101196-9-peter.maydell@linaro.org
Message-id: 20250217125055.160887-7-peter.maydell@linaro.org
The definition of which floatx80 encodings are invalid is
target-specific. Currently we handle this with an ifdef, but we
would like to defer this decision to runtime. In preparation, pass a
float_status argument to floatx80_invalid_encoding().
We will change the implementation from ifdef to looking at
the status argument in the following commit.
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: 20250224111524.1101196-7-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 handle flushing of output denormals in uncanon_normal
always before we deal with rounding. This works for architectures
that detect tininess before rounding, but is usually not the right
place when the architecture detects tininess after rounding. For
example, for x86 the SDM states that the MXCSR FTZ control bit causes
outputs to be flushed to zero "when it detects a floating-point
underflow condition". This means that we mustn't flush to zero if
the input is such that after rounding it is no longer tiny.
At least one of our guest architectures does underflow detection
after rounding but flushing of denormals before rounding (MIPS MSA);
this means we need to have a config knob for this that is separate
from our existing tininess_before_rounding setting.
Add an ftz_detection flag. For consistency with
tininess_before_rounding, we make it default to "detect ftz after
rounding"; this means that we need to explicitly set the flag to
"detect ftz before rounding" on every existing architecture that sets
flush_to_zero, so that this commit has no behaviour change.
(This means more code change here but for the long term a less
confusing API.)
For several architectures the current behaviour is either
definitely or possibly wrong; annotate those with TODO comments.
These architectures are definitely wrong (and should detect
ftz after rounding):
* x86
* Alpha
For these architectures the spec is unclear:
* MIPS (for non-MSA)
* RX
* SH4
PA-RISC makes ftz detection IMPDEF, but we aren't setting the
"tininess before rounding" setting that we ought to.
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
For the x86 and the Arm FEAT_AFP semantics, we need to be able to
tell the target code that the FPU operation has used an input
denormal. Implement this; when it happens we set the new
float_flag_denormal_input_used.
Note that we only set this when an input denormal is actually used by
the operation: if the operation results in Invalid Operation or
Divide By Zero or the result is a NaN because some other input was a
NaN then we never needed to look at the input denormal and do not set
denormal_input_used.
We mostly do not need to adjust the hardfloat codepaths to deal with
this flag, because almost all hardfloat operations are already gated
on the input not being a denormal, and will fall back to softfloat
for a denormal input. The only exception is the comparison
operations, where we need to add the check for input denormals, which
must now fall back to softfloat where they did not before.
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Currently in softfloat we canonicalize input denormals and so the
code that implements floating point operations does not need to care
whether the input value was originally normal or denormal. However,
both x86 and Arm FEAT_AFP require that an exception flag is set if:
* an input is denormal
* that input is not squashed to zero
* that input is actually used in the calculation (e.g. we
did not find the other input was a NaN)
So we need to track that the input was a non-squashed denormal. To
do this we add a new value to the FloatClass enum. In this commit we
add the value and adjust the code everywhere that looks at FloatClass
values so that the new float_class_denormal behaves identically to
float_class_normal. We will add the code that does the "raise a new
float exception flag if an input was an unsquashed denormal and we
used it" in a subsequent commit.
There should be no behavioural change in this commit.
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
In commit 8adcff4ae7 ("fpu: handle raising Invalid for infzero in
pick_nan_muladd") we changed the handling of 0 * Inf + QNaN to always
raise the Invalid exception regardless of target architecture. (This
was a change affecting hppa, i386, sh4 and tricore.) However, this
was incorrect for i386, which documents in the SDM section 14.5.2
that for the 0 * Inf + NaN case that it will only raise the Invalid
exception when the input is an SNaN. (This is permitted by the IEEE
754-2008 specification, which documents that whether we raise Invalid
for 0 * Inf + QNaN is implementation defined.)
Adjust the softfloat pick_nan_muladd code to allow the target to
suppress the raising of Invalid for the inf * zero + NaN case (as an
extra flag orthogonal to its choice for when to use the default NaN),
and enable that for x86.
We do not revert here the behaviour change for hppa, sh4 or tricore:
* The sh4 manual is clear that it should signal Invalid
* The tricore manual is a bit vague but doesn't say it shouldn't
* The hppa manual doesn't talk about fused multiply-add corner
cases at all
Cc: qemu-stable@nongnu.org
Fixes: 8adcff4ae7 (""fpu: handle raising Invalid for infzero in pick_nan_muladd")
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Link: https://lore.kernel.org/r/20250116112536.4117889-2-peter.maydell@linaro.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Our float_flag_output_denormal exception flag is set when
the fpu code flushes an output denormal to zero. Rename
it to float_flag_output_denormal_flushed:
* this keeps it parallel with the flag for flushing
input denormals, which we just renamed
* it makes it clearer that it doesn't mean "set when
the output is a denormal"
Commit created with
for f in `git grep -l float_flag_output_denormal`; do sed -i -e 's/float_flag_output_denormal/float_flag_output_denormal_flushed/' $f; done
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20250124162836.2332150-21-peter.maydell@linaro.org
Our float_flag_input_denormal exception flag is set when the fpu code
flushes an input denormal to zero. This is what many guest
architectures (eg classic Arm behaviour) require, but it is not the
only donarmal-related reason we might want to set an exception flag.
The x86 behaviour (which we do not currently model correctly) wants
to see an exception flag when a denormal input is *not* flushed to
zero and is actually used in an arithmetic operation. Arm's FEAT_AFP
also wants these semantics.
Rename float_flag_input_denormal to float_flag_input_denormal_flushed
to make it clearer when it is set and to allow us to add a new
float_flag_input_denormal_used next to it for the x86/FEAT_AFP
semantics.
Commit created with
for f in `git grep -l float_flag_input_denormal`; do sed -i -e 's/float_flag_input_denormal/float_flag_input_denormal_flushed/' $f; done
and manual editing of softfloat-types.h and softfloat.c to clean
up the indentation afterwards and to fix a comment which wasn't
using the full name of the flag.
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20250124162836.2332150-20-peter.maydell@linaro.org
Certain Hexagon instructions suppress changes to the result
when the product of fma() is a true zero.
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
All uses have been convered to float*_muladd_scalbn.
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
We currently have a flag, float_muladd_halve_result, to scale
the result by 2**-1. Extend this to handle arbitrary scaling.
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Replace the "index" selecting between A and B with a result variable
of the proper type. This improves clarity within the function.
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-id: 20241203203949.483774-12-richard.henderson@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Move the fractional comparison to the end of the
float_2nan_prop_x87 case. This is not required for
any other 2nan propagation rule. Reorganize the
x87 case itself to break out of the switch when the
fractional comparison is not required.
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 20241203203949.483774-11-richard.henderson@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Remember if there was an SNaN, and use that to simplify
float_2nan_prop_s_{ab,ba} to only the snan component.
Then, fall through to the corresponding
float_2nan_prop_{ab,ba} case to handle any remaining
nans, which must be quiet.
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 20241203203949.483774-10-richard.henderson@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Inline pickNaN into its only caller. This makes one assert
redundant with the immediately preceding IF.
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-id: 20241203203949.483774-9-richard.henderson@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Unpacking and repacking the parts may be slightly more work
than we did before, but we get to reuse more code. For a
code path handling exceptional values, this is an improvement.
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20241203203949.483774-8-richard.henderson@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
This function is part of the public interface and
is not "specialized" to any target in any way.
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 20241203203949.483774-7-richard.henderson@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
While all indices into val[] should be in [0-2], the mask
applied is two bits. To help static analysis see there is
no possibility of read beyond the end of the array, pad the
array to 4 entries, with the final being (implicitly) NULL.
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-id: 20241203203949.483774-6-richard.henderson@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Assign the pointer return value to 'a' directly,
rather than going through an intermediary index.
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-id: 20241203203949.483774-5-richard.henderson@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Remove "3" as a special case for which and simply
branch to return the desired value.
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-id: 20241203203949.483774-4-richard.henderson@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Inline pickNaNMulAdd into its only caller. This makes
one assert redundant with the immediately preceding IF.
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-id: 20241203203949.483774-3-richard.henderson@linaro.org
[PMM: keep comment from old code in new location]
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Now that all our targets have bene converted to explicitly specify
their pattern for the default NaN value we can remove the remaining
fallback code in parts64_default_nan().
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20241202131347.498124-55-peter.maydell@linaro.org
Set the default NaN pattern explicitly for hexagon.
Remove the ifdef from parts64_default_nan(); the only
remaining unconverted targets all use the default case.
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20241202131347.498124-52-peter.maydell@linaro.org
Set the default NaN pattern explicitly for SPARC, and remove
the ifdef from parts64_default_nan.
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20241202131347.498124-50-peter.maydell@linaro.org
Set the default NaN pattern explicitly for m68k.
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20241202131347.498124-43-peter.maydell@linaro.org
Set the default NaN pattern explicitly, and remove the ifdef from
parts64_default_nan().
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20241202131347.498124-39-peter.maydell@linaro.org
Set the default NaN pattern explicitly, and remove the ifdef from
parts64_default_nan().
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20241202131347.498124-38-peter.maydell@linaro.org
Set the default NaN pattern explicitly, and remove the ifdef from
parts64_default_nan().
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20241202131347.498124-37-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
Set the Float3NaNPropRule explicitly for xtensa, and remove the
ifdef from pickNaNMulAdd().
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20241202131347.498124-24-peter.maydell@linaro.org
Set the Float3NaNPropRule explicitly for Arm, and remove the
ifdef from pickNaNMulAdd().
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20241202131347.498124-23-peter.maydell@linaro.org
Set the Float3NaNPropRule explicitly for SPARC, and remove the
ifdef from pickNaNMulAdd().
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20241202131347.498124-22-peter.maydell@linaro.org
Set the Float3NaNPropRule explicitly for s390x, and remove the
ifdef from pickNaNMulAdd().
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20241202131347.498124-21-peter.maydell@linaro.org
Set the Float3NaNPropRule explicitly for PPC, and remove the
ifdef from pickNaNMulAdd().
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20241202131347.498124-20-peter.maydell@linaro.org
Set the Float3NaNPropRule explicitly for loongarch, and remove the
ifdef from pickNaNMulAdd().
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20241202131347.498124-19-peter.maydell@linaro.org
Set the Float3NaNPropRule explicitly for Arm, and remove the
ifdef from pickNaNMulAdd().
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20241202131347.498124-18-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
Set the FloatInfZeroNaNRule explicitly for the loongarch target.
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20241202131347.498124-13-peter.maydell@linaro.org
Richard Henderson
Peter Maydell