Seismograph Absolute Trace
Signals & AudioSigned 64-bit samples cross zero while two independent absolute-value forms rectify them into the same bright envelope.
Self-running — verified CRC 8490.
Click the screen, then play. (Tab away and it pauses.)
The operation under test
The trace feeds positive and negative 64-bit values through both the C library llabs function and the canonical x < 0 ? -x : x idiom. Samples cross the 16-, 32-, and 48-bit limb boundaries and include INT64_MIN+1, the largest legal negative magnitude; INT64_MIN is deliberately excluded because negating it is undefined in C.
Compiler shape: signed i64 absolute value forms in LLVM IR and passes the non-LTO machine verifier.
Result: host, default, a16, and xy16 all return 0x8490 on MAME and bsnes-jg.
What the scope shows
Gold is the signed input around the blue zero line. Cyan is its rectified magnitude mirrored above and below; the tallest pulse is the INT64_MIN+1 case. Every plotted point comes from the same values folded into the differential CRC.
Compiler stress-test #121, Round 7. Source and full test record live in llvm-mos-65816.