Fix 5xy0 comparison & full font load (+ opcode tests)#2
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- 5xy0 skipped when Vx != Vy; the CHIP-8 spec skips when Vx == Vy (9xy0 is the 'not equal' variant). Inverted comparison fixed. - InitiateChip8 copied only 10 of the 80 font bytes, leaving glyphs 2..F blank while Fx29 addresses them at Vx*5. Load the whole fontSet.
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What
Fixes two emulation bugs in
emul8/emul8.goand adds the first opcode test suite.Bug 1 —
5xy0comparison inverted5xy0("skip next ifVx == Vy") was implemented with!=, i.e. it behaved like9xy0. Any ROM relying onSE Vx, Vywould branch the wrong way. Fixed to==.Bug 2 — only 10 of 80 font bytes loaded
InitiateChip8copiedfontSetwithfor i := 0; i < 10, loading just glyphs0and1.Fx29addresses each glyph atVx*5, so glyphs2–Fpointed at zeroed memory andrendered blank. Now loads the full 80-byte set.
Tests —
emul8/emul8_test.go(standardtesting, white-box)Covers
6xnn/7xnn,5xy0/9xy0,8xy4carry,8xy5borrow,Annn/Bnnn,Fx33BCD,
Fx55/Fx65store-load,2nnn/00EEcall-return, and3xnn/4xnn. Two areregression tests pinning the fixes above. CI now runs
go test ./...alongside build/vet.How to verify
go test ./...