Another bit of behavior that we weren't performing correctly is the
unsetting of FPSCR.FI and FPSCR.FR when FPSCR.ZX is supposed to be set.
This is supported in PEM's section 3.3.6.1 where the following is
stated:
"
When a zero divide condition occurs, the following actions are taken:
- Zero divide exception condition bit is set FPSCR[ZX] = 1.
- FPSCR[FR, FI] are cleared.
"
And so, this fixes that behavior.
FPSCR[ZX] is the bit defined to represent the zero divide exception
condition bit, and is defined as (according to PowerPC Microprocessor
Family: The Programming Environments Manual for 32 and 64-bit
Microprocessors, which will be referred to as "PEM" for the rest of this
commit message) at section 3.3.6.1:
"
A zero divide exception condition occurs when a divide instructions is
executed with a zero divisor value and a finite, nonzero dividend value
or when a floating reciprocal estimate single (fres) or a floating
reciprocal square root estimate (frsqrte) instruction is executed with a
zero operand value.
"
Note that it states the divisor must be zero and the dividend must be
nonzero in order for ZX to be set. This means that the interpreter was
performing the wrong behavior for the case where 0/0 (with any sign on
the zeros) is performed. We would incorrectly set the ZX bit when only
the VXZDZ bit should be set.
It's also worth pointing out that N/0 (where N is any finite nonzero
value) and 0/0 are not within the same exception class. N/0 is a zero
divide exception case, while 0/0 is considered an invalid operation
exception case, which is also indicated in the PEM section 3.3.6.1 as
well where it lists the criteria for invalid operation exceptions.
Therefore we should only be setting the VXZDZ bit in the 0/0 case, not
VXZDZ and ZX. This was also verified via hardware tests to ensure that
this behavior indeed holds.
Fairly trivial to resolve, we just initialize the std::array with two
sets of braces (one set to create the array, the other to start and end the
aggregate data that we'll end up returning)
Given this is actually a part of the Host interface, this should be
placed with it.
While we're at it, turn it into an enum class so that we don't dump its
contained values into the surrounding scope. We can also make
Host_Message take the enum type itself directly instead of taking a
general int value.
After this, it'll be trivial to divide out the rest of Common.h and
remove the header from the repository entirely
If invalid operation exceptions are enabled and an invalid operation
occurs, then the destination value remains untouched. This fixes issues
that may arise when using these two instructions where the destination
gets steamrolled by an infinity or NaN value.
If a NaN of any type is passed as the operand to either of these
instructions, we shouldn't go down the regular code path, as we end up
potentially setting the wrong flags. For example, we wouldn't set the
FPSCR.VXCVI bit properly. We'd also set FPSCR.FI, when in actuality it
should be unset.
If an SNaN is passed as an operand, we also need to set the FPSCR.VXSNAN
bit as well.
The flag setting behavior for these can be found in Appendix C.4.2 in
PowerPC Microprocessor Family: The Programming Environments Manual for
32 and 64-bit Microprocessors.
fctiwz functions in the same manner as fctiw, with the difference being
that fctiwz always assumes the rounding mode being towards zero. Because
of this, we can implement fctiwz in terms of fctiw's code, but modify it
to accept a rounding mode, allowing us to preserve proper behavior for
both instructions.
We also move Helper_UpdateCR1 to a temporary home in
Interpreter_FPUtils.h for the time being. It would be more desirable to
move it to a new common header for all the helpers, so that even JITs
can use them if they so wish, however, this and the following changes
are intended to only touch the interpreter to keep changes minimal for
fixing instruction behavior.
JitCommon already duplicates the Helper_Mask function within
JitBase.cpp/.h, and the ARM JIT includes the Interpreter header in order
to call Helper_Carry. So a follow up is best suited here, as this
touches two other CPU backends.
We can just memcpy the data instead of pointer-casting data, which is
alignment-safe and doesn't run afoul of aliasing rules.
Previously it also made it seem as if data itself pointed to valid
usable data, but it doesn't, it simply functions as an out parameter
where we push data built up from the GetState() functions into it.
This was added in 4bdb4aa0d1 back in
2009-02-27. The only usage spot of this macro involves the same checks
that were used to define that preprocessor macro, so we can simply
remove the macro
Léo Lam