Motion-Detect Difference Field
Signals & AudioTwo drifting signals become three synchronized difference silhouettes, proving the compiler lowers absolute subtraction correctly at every tested width.
Self-running — verified CRC 3482.
Click the screen, then play. (Tab away and it pauses.)
The operation under test
The common expression a > b ? a - b : b - a can be recognized by LLVM as an absolute-difference operation. This ROM forms that expression for unsigned 8-bit, signed 16-bit, and unsigned 32-bit values, then checks the selected lowering against the same host model.
Visible proof: the three separated bands run the same drifting source geometry through u8, s16, and u32 kernels. Cyan edges and yellow motion silhouettes are computed from the actual probe results; the bottom strip tracks difference energy.
Result: host, default, a16, and xy16 all return 0x3482. No compiler defect was found.
Why three widths?
Each width takes a different legalization path on this 8/16-bit target. Running them together catches both missing opcode coverage and errors in multi-limb subtraction while keeping the visual result directly comparable.
Compiler stress-test #119, Round 7. Source and full test record live in llvm-mos-65816.