PowerPC has a 32 bit CR register, which is used to store flags for results of
computations. Most instructions have an optional bit that tells the CPU whether
the flags should be updated. This 32 bit register actually contains 8 sets of 4
flags: Summary Overflow (SO), Equals (EQ), Greater Than (GT), Less Than (LT).
These 8 sets are usually called CR0-CR7 and accessed independently. In the most
common operations, the flags are computed from the result of the operation in
the following fashion:
* EQ is set iff result == 0
* LT is set iff result < 0
* GT is set iff result > 0
* (Dolphin does not emulate SO)
While X86 architectures have a similar concept of flags, it is very difficult
to access the FLAGS register directly to translate its value to an equivalent
PowerPC value. With the current Dolphin implementation, updating a PPC CR
register requires CPU branching, which has a few performance issues: it uses
space in the BTB, and in the worst case (!GT, !LT, EQ) requires 2 branches not
taken.
After some brainstorming on IRC about how this could be improved, calc84maniac
figured out a neat trick that makes common CR operations way more efficient to
JIT on 64 bit X86 architectures. It relies on emulating each CRn bitfield with
a 64 bit register internally, whose value is the result of the operation from
which flags are updated, sign extended to 64 bits. Then, checking if a CR bit
is set can be done in the following way:
* EQ is set iff LOWER_32_BITS(cr_64b_val) == 0
* GT is set iff (s64)cr_64b_val > 0
* LT is set iff bit 62 of cr_64b_val is set
To take a few examples, if the result of an operation is:
* -1 (0xFFFFFFFFFFFFFFFF) -> lower 32 bits not 0 => !EQ
-> (s64)val (-1) is not > 0 => !GT
-> bit 62 is set => LT
!EQ, !GT, LT
* 0 (0x0000000000000000) -> lower 32 bits are 0 => EQ
-> (s64)val (0) is not > 0 => !GT
-> bit 62 is not set => !LT
EQ, !GT, !LT
* 1 (0x0000000000000001) -> lower 32 bits not 0 => !EQ
-> (s64)val (1) is > 0 => GT
-> bit 62 is not set => !LT
!EQ, GT, !LT
Sometimes we need to convert PPC CR values to these 64 bit values. The
following convention is used in this case:
* Bit 0 (LSB) is set iff !EQ
* Bit 62 is set iff LT
* Bit 63 is set iff !GT
* Bit 32 always set to disambiguize between EQ and GT
Some more examples:
* !EQ, GT, LT -> 0x4000000100000001 (!B63, B62, B32, B0)
-> lower 32 bits not 0 => !EQ
-> (s64)val is > 0 => GT
-> bit 62 is set => LT
* EQ, GT, !LT -> 0x0000000100000000
-> lower 32 bits are 0 => EQ
-> (s64)val is > 0 (note: B32) => GT
-> bit 62 is not set => !LT
It was only used for Windows XP and lower.
This also bumps the _WIN32_WINNT define in the stdafx precompiled headers to set the minimum version as Windows Vista.
CheckDeviceType_Write uses an OVERLAPPED structure to make sure some bytes
were written to the device for a given _IOWrite operation. However, the
OVERLAPPED structure is only used for the BlueSoleil stack, not the MS stack
(which goes through an alternate HID path instead of WriteFile, and does not
have an equivalent async operation).
Make _IOWrite return the number of written bytes instead, since it knows
about the Bluetooth stack being used.
This error code is used by third-party WiiMote adapters to signal the
absence of a WiiMote connected to their virtual HID port. Ignoring it
removes some log spamming and doesn't change anything in terms of
behavior.
This ensures the transition from/to exclusive mode happens while the RenderFrame is fullscreen.
This prevents fullscreen loops and relieves us of having to restore the window size after we exit fullscreen.
Pierre Bourdon