0.14.0 — Conditional Branches and a Decoder

Version 0.14.0 (0.13.0 was skipped) did two things that changed how the project validated itself from this point forward.

INC/DEC and JZ/JNZ

e0269d1 — Update project version to 0.14.0, add INC and DEC instructions, and implement conditional jumps (JZ, JNZ) gave Kasm its first real loop primitive: increment or decrement eax, then branch on whether the result was zero. Combined with the near/short jumps from 0.10.0, this was enough to express a counted loop for the first time.

A decoder, and a new kind of test

1ec928a — Implement decoding functionality and update tests for new instructions added a decoder — the mirror image of the encoder, turning an image back into a textual listing. This changed the testing strategy: up to this point, tests compared encoded hex against expected hex. From here on, tests could also compare a decoded listing against expected text, which catches a different class of bug (an encoder and decoder can independently agree on the wrong thing, but round-tripping through both makes an encoding error much more likely to surface as a decoding error too).

This decoder is also the origin of a bug that took several versions to surface. Because new instructions were added to the encoder and their decoder entries sometimes lagged behind, inc eax and jz briefly had correct encodings but incomplete decoding support — a gap the 0.18.1 milestone (see the next chapter) closed with a dedicated regression test.

With INC/DEC and JZ/JNZ in place, and a decoder to check work against, the project moved on to broadening the arithmetic instruction set: ADD, SUB, and several bitwise operations, all following the same “parse → validate → encode → decode” pattern established here.