This patch modifies SoftFloat library so that it can be configured in
run-time in relation to the meaning of signaling NaN bit, while, at the
same time, strictly preserving its behavior on all existing platforms.
Background:
In floating-point calculations, there is a need for denoting undefined or
unrepresentable values. This is achieved by defining certain floating-point
numerical values to be NaNs (which stands for "not a number"). For additional
reasons, virtually all modern floating-point unit implementations use two
kinds of NaNs: quiet and signaling. The binary representations of these two
kinds of NaNs, as a rule, differ only in one bit (that bit is, traditionally,
the first bit of mantissa).
Up to 2008, standards for floating-point did not specify all details about
binary representation of NaNs. More specifically, the meaning of the bit
that is used for distinguishing between signaling and quiet NaNs was not
strictly prescribed. (IEEE 754-2008 was the first floating-point standard
that defined that meaning clearly, see [1], p. 35) As a result, different
platforms took different approaches, and that presented considerable
challenge for multi-platform emulators like QEMU.
Mips platform represents the most complex case among QEMU-supported
platforms regarding signaling NaN bit. Up to the Release 6 of Mips
architecture, "1" in signaling NaN bit denoted signaling NaN, which is
opposite to IEEE 754-2008 standard. From Release 6 on, Mips architecture
adopted IEEE standard prescription, and "0" denotes signaling NaN. On top of
that, Mips architecture for SIMD (also known as MSA, or vector instructions)
also specifies signaling bit in accordance to IEEE standard. MSA unit can be
implemented with both pre-Release 6 and Release 6 main processor units.
QEMU uses SoftFloat library to implement various floating-point-related
instructions on all platforms. The current QEMU implementation allows for
defining meaning of signaling NaN bit during build time, and is implemented
via preprocessor macro called SNAN_BIT_IS_ONE.
On the other hand, the change in this patch enables SoftFloat library to be
configured in run-time. This configuration is meant to occur during CPU
initialization, at the moment when it is definitely known what desired
behavior for particular CPU (or any additional FPUs) is.
The change is implemented so that it is consistent with existing
implementation of similar cases. This means that structure float_status is
used for passing the information about desired signaling NaN bit on each
invocation of SoftFloat functions. The additional field in float_status is
called snan_bit_is_one, which supersedes macro SNAN_BIT_IS_ONE.
IMPORTANT:
This change is not meant to create any change in emulator behavior or
functionality on any platform. It just provides the means for SoftFloat
library to be used in a more flexible way - in other words, it will just
prepare SoftFloat library for usage related to Mips platform and its
specifics regarding signaling bit meaning, which is done in some of
subsequent patches from this series.
Further break down of changes:
1) Added field snan_bit_is_one to the structure float_status, and
correspondent setter function set_snan_bit_is_one().
2) Constants <float16|float32|float64|floatx80|float128>_default_nan
(used both internally and externally) converted to functions
<float16|float32|float64|floatx80|float128>_default_nan(float_status*).
This is necessary since they are dependent on signaling bit meaning.
At the same time, for the sake of code cleanup and simplicity, constants
<floatx80|float128>_default_nan_<low|high> (used only internally within
SoftFloat library) are removed, as not needed.
3) Added a float_status* argument to SoftFloat library functions
XXX_is_quiet_nan(XXX a_), XXX_is_signaling_nan(XXX a_),
XXX_maybe_silence_nan(XXX a_). This argument must be present in
order to enable correct invocation of new version of functions
XXX_default_nan(). (XXX is <float16|float32|float64|floatx80|float128>
here)
4) Updated code for all platforms to reflect changes in SoftFloat library.
This change is twofolds: it includes modifications of SoftFloat library
functions invocations, and an addition of invocation of function
set_snan_bit_is_one() during CPU initialization, with arguments that
are appropriate for each particular platform. It was established that
all platforms zero their main CPU data structures, so snan_bit_is_one(0)
in appropriate places is not added, as it is not needed.
[1] "IEEE Standard for Floating-Point Arithmetic",
IEEE Computer Society, August 29, 2008.
Backports commit af39bc8c49224771ec0d38f1b693ea78e221d7bc from qemu
Make the functions which convert floating point to 16 bit integer
return int16_t rather than int_fast16_t, and correspondingly use
int_fast16_t in their internal implementations where appropriate.
(These functions are used only by the ARM target.)
Backports commit 0bb721d7217ed4a1abb44f521c5c7ec185062d58 from qemu
Replace the uint8 softfloat-specific typedef with uint8_t.
This change was made with
find include hw fpu target-* -name '*.[ch]' | xargs sed -i -e 's/\buint8\b/uint8_t/g'
together with manual removal of the typedef definition and
manual fixing of more erroneous uses found via test compilation.
It turns out that the only code using this type is an accidental
use where uint8_t was intended anyway...
Backports commit d341d9f3062c74d74c94ebe6359f067bed8311ba from qemu
Replace the int8 softfloat-specific typedef with int8_t.
This change was made with
find include hw fpu target-* -name '*.[ch]' | xargs sed -i -e 's/\bint8\b/int8_t/g'
together with manual removal of the typedef definition, and
manual undoing of various mis-hits.
Backports commit 8f506c709adb7d3bed4ebefefe9487c156192a64 from qemu
Replace the uint32 softfloat-specific typedef with uint32_t.
This change was made with
find include hw fpu target-* -name '*.[ch]' | xargs sed -i -e 's/\buint32\b/uint32_t/g'
together with manual removal of the typedef definition,
manual undoing of various mis-hits, and another couple of
fixes found via test compilation.
All the uses in hw/ were using the wrong type by mistake.
Backports commit 3a87d00910ef64a2eece4aad25d96ea10683fc5c from qemu
Replace the int32 softfloat-specific typedef with int32_t.
This change was made with
find hw include fpu target-* -name '*.[ch]' | xargs sed -i -e 's/\bint32\b/int32_t/g'
together with manual removal of the typedef definition, and
manual undoing of some mis-hits where macro arguments were
being used for token pasting rather than as a type.
The uses in hw/ipmi/ should not have been using this type at all.
Backports commit f4014512cda682a9d0c75310d278d7ae96b0505c from qemu
Replace the uint64 softfloat-specific typedef with uint64_t.
This change was made with
find include fpu target-* -name '*.[ch]' | xargs sed -i -e 's/\buint64\b/uint64_t/g'
together with manual removal of the typedef definition, and
manual undoing of some mis-hits where macro arguments were
being used for token pasting rather than as a type.
Note that the target-mips/kvm.c and target-s390x/kvm.c changes are fixing
code that should not have been using the uint64 type in the first place.
Backports commit 182f42fdc219e6481654fcfb73b17e4b4e63b6ff from qemu
Replace the int64 softfloat-specific typedef with int64_t.
This change was made with
find include fpu target-* -name '*.[ch]' | xargs sed -i -e 's/\bint64\b/int64_t/g'
together with manual removal of the typedef definition, and
manual undoing of some mis-hits where macro arguments were
being used for token pasting rather than as a type.
Backports commit f42c222482b651400f0fa417eb174da1c9502c1c from qemu
The code in the softfloat source files is under a mixture of
licenses: the original code and many changes from QEMU contributors
are under the base SoftFloat-2a license; changes from Stefan Weil
and RedHat employees are GPLv2-or-later; changes from Fabrice Bellard
are under the BSD license. Clarify this in the comments at the
top of each affected source file, including a statement about
the assumed licensing for future contributions, so we don't need
to remember to ask patch submitters explicitly to pick a license.
Backports commit 16017c48547960539fcadb1f91d252124f442482 from qemu
Revert the remaining portions of commits 75d62a5856 and 3430b0be36f
which are under a SoftFloat-2b license, ie the functions
uint64_to_float32() and uint64_to_float64(). (The float64_to_uint64()
and float64_to_uint64_round_to_zero() functions were completely
rewritten in commits fb3ea83aa and 0a87a3107d so can stay.)
Reimplement from scratch the uint64_to_float64() and uint64_to_float32()
conversion functions.
[This is a mechanical squashing together of two separate "revert"
and "reimplement" patches.]
Backports commit 6bb8e0f130bd4aecfe835a0caa94390fa2235fde from qemu
This commit applies the changes to master which correspond to
replacing commit 158142c2c2df with a set of changes made by:
* taking the SoftFloat-2a release
* mechanically transforming the block comment style
* reapplying Fabrice's original changes from 158142c2c2df
This commit was created by:
diff -u 158142c2c2df import-sf-2a
patch -p1 --fuzz 10 <../relicense-patch.txt
(where import-sf-2a is the branch resulting from the changes above).
Backports commit a7d1ac78e0f1101df2ff84502029a4b0da6024ae from qemu
