fix(libSceMouse): round ExtensionScalePosition up, as the module does

@BunnyFl's emulation of the 13.42 instructions shows a ceiling, not
rounding to nearest: the floor from the 0x80008001 multiply gets 1 added
whenever the remainder isn't 0. The test adds (1, 2) and (32767, 2),
which give 1 by ceiling and 0 by rounding.

core/libs/prx/libSceMouse/Export.cpp

@@ -143,7 +143,7 @@ int APS5_VABI sceMouseExtensionScalePosition(std::uint16_t* position, std::uint1
     if (!Mouse::IsInitialized()) return MOUSE_ERROR_NOT_INITIALIZED;
     if (position == nullptr || scale == 0) return MOUSE_ERROR_INVALID_ARG;
     const std::uint32_t scaled = static_cast<std::uint32_t>(*position) * (scale - 1u);
-    *position = static_cast<std::uint16_t>((scaled + 0x7fffu) / 0xffffu);
+    *position = static_cast<std::uint16_t>((scaled + 0xfffeu) / 0xffffu);
     return MOUSE_OK;
 }
 

core/libs/prx/libSceMouse/tests/MouseQueries.cpp

@@ -70,10 +70,10 @@ int main() {
 
     Require(scale(nullptr, 1920) == InvalidArg, "ExtensionScalePosition took a null position");
     Require(scale(&position, 0) == InvalidArg && position == 100, "ExtensionScalePosition took a scale of 0");
-    const std::array<std::array<std::uint16_t, 3>, 6> rows{{{65535, 1920, 1919}, {32768, 1920, 960}, {0, 1920, 0}, {65535, 1, 0}, {1, 65535, 1}, {40000, 1080, 659}}};
+    const std::array<std::array<std::uint16_t, 3>, 9> rows{{{65535, 1920, 1919}, {32768, 1920, 960}, {0, 1920, 0}, {65535, 1, 0}, {1, 65535, 1}, {40000, 1080, 659}, {1, 2, 1}, {32767, 2, 1}, {100, 1920, 3}}};
     for (const auto& [input, size, expected] : rows) {
         position = input;
-        Require(scale(&position, size) == Ok && position == expected, "ExtensionScalePosition didn't round position * (scale - 1) / 65535");
+        Require(scale(&position, size) == Ok && position == expected, "ExtensionScalePosition didn't round position * (scale - 1) / 65535 up");
     }
 
     Require(setConfig(handle, nullptr) == InvalidArg, "ExtensionSetConfig took a null config");

docs/dev/debt/libSceMouse.md

@@ -15,7 +15,7 @@
 - [sceMouseGetHandle, sceMouseExtensionSetConfig and sceMouseExtensionScalePosition](../../../core/libs/prx/libSceMouse/src/mouse_impl.cpp) (libSceMouse) - follow the same [13.42 disassembly](https://github.com/boykopovar/AnyPS5/issues/15088#issuecomment-6580877653), not a console; none reaches the driver.
   - `GetHandle(userId, type, index)` returns the handle `sceMouseOpen` gave that user and type, or 0x80df0008. The console skips slots whose +0xc8 field is 1 when `index` is non-zero; that field's meaning is unknown, and no slot here has it.
   - `ExtensionSetConfig(handle, config)` refuses a null or a non-zero byte in 5..0x1f, then stores the u32 at 0 and the byte at 4; nothing here reads them yet.
-  - `ExtensionScalePosition(uint16* position, uint16 scale)` rounds `*position * (scale - 1) / 65535` to the nearest integer, which has no ties since 65535 is odd. The console divides with a multiply by 0x80008001 and a shift by 47, which equals that floor division for every product of two 16-bit values, then rounds with a compare whose exact form wasn't checked.
+  - `ExtensionScalePosition(uint16* position, uint16 scale)` rounds `*position * (scale - 1) / 65535` up. The console divides with a multiply by 0x80008001 and a shift by 47, which is the floor, and adds 1 when the remainder isn't 0, through a compare of `-(product * 65537)` with 0x10002 ([@BunnyFl's emulation]()).
 
 - [Publish](../../../core/libs/prx/libSceMouse/src/mouse_impl.cpp) (libSceMouse) - consecutive motion-only reports with the same buttons are summed into the newest unread entry, so a title that reads a few entries per frame gets current motion instead of a full queue of old reports. Reports with no motion and no button, wheel, tilt or connection change are dropped. Per-report granularity and the console's own report rate are not reproduced