fpu: Move m68k_denormal fmt flag into floatx80_behaviour

Currently we compile-time set an 'm68k_denormal' flag in the FloatFmt
for floatx80 for m68k. This controls our handling of what the Intel
do

fpu: Move m68k_denormal fmt flag into floatx80_behaviour

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

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fpu: Make floatx80 invalid encoding settable at runtime

Because floatx80 has an explicit integer bit, this permits some
odd encodings where the integer bit is not set correctly for the
floating poin

fpu: Make floatx80 invalid encoding settable at runtime

Because floatx80 has an explicit integer bit, this permits some
odd encodings where the integer bit is not set correctly for the
floating point value type. In In Intel terminology the
categories are:
exp == 0, int = 0, mantissa == 0 : zeroes
exp == 0, int = 0, mantissa != 0 : denormals
exp == 0, int = 1 : pseudo-denormals
0 < exp < 0x7fff, int = 0 : unnormals
0 < exp < 0x7fff, int = 1 : normals
exp == 0x7fff, int = 0, mantissa == 0 : pseudo-infinities
exp == 0x7fff, int = 1, mantissa == 0 : infinities
exp == 0x7fff, int = 0, mantissa != 0 : pseudo-NaNs
exp == 0x7fff, int = 1, mantissa == 0 : NaNs

The usual IEEE cases of zero, denormal, normal, inf and NaN are always valid.
x87 permits as input also pseudo-denormals.
m68k permits all those and also pseudo-infinities, pseudo-NaNs and unnormals.

Currently we have an ifdef in floatx80_invalid_encoding() to select
the x86 vs m68k behaviour. Add new floatx80_behaviour flags to
select whether pseudo-NaN and unnormal are valid, and use these
(plus the existing pseudo_inf_valid flag) to decide whether these
encodings are invalid at runtime.

We leave pseudo-denormals as always-valid, since both x86 and m68k
accept them.

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: 20250224111524.1101196-8-peter.maydell@linaro.org
Message-id: 20250217125055.160887-6-peter.maydell@linaro.org

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fpu: Pass float_status to floatx80_invalid_encoding()

The definition of which floatx80 encodings are invalid is
target-specific. Currently we handle this with an ifdef, but we
would like to defer t

fpu: Pass float_status to floatx80_invalid_encoding()

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

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fpu: Make targets specify whether floatx80 Inf can have Int bit clear

In Intel terminology, a floatx80 Infinity with the explicit integer
bit clear is a "pseudo-infinity"; for x86 these are not vali

fpu: Make targets specify whether floatx80 Inf can have Int bit clear

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

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fpu: Pass float_status to floatx80_is_infinity()

Unlike the other float formats, whether a floatx80 value is
considered to be an Infinity is target-dependent. (On x86 if the
explicit integer bit is

fpu: Pass float_status to floatx80_is_infinity()

Unlike the other float formats, whether a floatx80 value is
considered to be an Infinity is target-dependent. (On x86 if the
explicit integer bit is clear this is a "pseudo-infinity" and not a
valid infinity; m68k does not care about the value of the integer
bit.)

Currently we select this target-specific logic at compile time with
an ifdef. We're going to want to do this at runtime, so change the
floatx80_is_infinity() function to take a float_status.

This commit doesn't change any logic; we'll do that in the
next 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: 20250224111524.1101196-5-peter.maydell@linaro.org

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fpu: Make targets specify floatx80 default Inf at runtime

Currently we hardcode at compile time whether the floatx80 default
Infinity value has the explicit integer bit set or not (x86 sets it;
m68k

fpu: Make targets specify floatx80 default Inf at runtime

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

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fpu: allow flushing of output denormals to be after rounding

Currently we handle flushing of output denormals in uncanon_normal
always before we deal with rounding. This works for architectures
tha

fpu: allow flushing of output denormals to be after rounding

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>

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fpu: Implement float_flag_input_denormal_used

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 thi

fpu: Implement float_flag_input_denormal_used

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>

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target/i386: Do not raise Invalid for 0 * Inf + QNaN

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

target/i386: Do not raise Invalid for 0 * Inf + QNaN

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>

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fpu: Fix a comment in softfloat-types.h

In softfloat-types.h a comment documents that if the float_status
field flush_to_zero is set then we flush denormalised results to 0
and set the inexact flag.

fpu: Fix a comment in softfloat-types.h

In softfloat-types.h a comment documents that if the float_status
field flush_to_zero is set then we flush denormalised results to 0
and set the inexact flag. This isn't correct: the status flag that
we set when flush_to_zero causes us to flush an output to zero is
float_flag_output_denormal_flushed.

Correct the comment.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20250124162836.2332150-22-peter.maydell@linaro.org

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fpu: Rename float_flag_output_denormal to float_flag_output_denormal_flushed

Our float_flag_output_denormal exception flag is set when
the fpu code flushes an output denormal to zero. Rename
it to f

fpu: Rename float_flag_output_denormal to float_flag_output_denormal_flushed

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

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fpu: Rename float_flag_input_denormal to float_flag_input_denormal_flushed

Our float_flag_input_denormal exception flag is set when the fpu code
flushes an input denormal to zero. This is what many

fpu: Rename float_flag_input_denormal to float_flag_input_denormal_flushed

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

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softfloat: Constify helpers returning float_status field

These helpers don't alter float_status. Make it const.

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Richard Hender

softfloat: Constify helpers returning float_status field

These helpers don't alter float_status. Make it const.

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-ID: <20250116214359.67295-1-philmd@linaro.org>

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softfloat: Add float_muladd_suppress_add_product_zero

Certain Hexagon instructions suppress changes to the result
when the product of fma() is a true zero.

Signed-off-by: Richard Henderson <richard

softfloat: Add float_muladd_suppress_add_product_zero

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>

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softfloat: Add float_round_nearest_even_max

This rounding mode is used by Hexagon.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

softfloat: Remove float_muladd_halve_result

All uses have been convered to float*_muladd_scalbn.

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Richard Henderson <richard.he

softfloat: Remove float_muladd_halve_result

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>

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softfloat: Add float{16,32,64}_muladd_scalbn

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 Mathi

softfloat: Add float{16,32,64}_muladd_scalbn

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>

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