FA-89787 / Instruction set emulation / Member archive

Rotate left is circular instead of through carry · case 02

rol feeds bit 7 back into bit 0 instead of the carry flag.

Member previewVariant 2 · 3 implementations · 8 checks per implementation

Case contract

Input [a, c, ops] with ops asl, lsr, rol, ror, asr on an 8-bit value and a carry bit. asl: C = bit 7, shift left. lsr: C = bit 0, shift right with 0. rol: shift left, bit 0 = old C, new C = old bit 7. ror: shift right, bit 7 = old C, new C = old bit 0. asr: C = bit 0, shift right keeping bit 7. Report [A, C, Z, N] after each op.

Why this case matters

Rotate-through-carry instructions implement multi-byte shifts in 8-bit code; emulating them with circular rotates or sequenced updates breaks arithmetic libraries.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
rotate left through carry	`[[3, 1, 0, 0], [6, 0, 0, 0], [12, 0, 0, 0], [24, 0, 0, 0], [48, 0, 0, 0]]`	`[[2, 1, 0, 0], [5, 0, 0, 0], [10, 0, 0, 0], [20, 0, 0, 0], [40, 0, 0, 0]]`	Failed

MEMBER ARCHIVE

The complete case is available to members.

This record includes three runnable implementations, regression fixtures, execution results, and source hashes.

Member access is invitation-based. Sign in with your invited account to inspect the sources.