FA-90268 / Bytecode virtual machines / Member archive

Switch dispatch: table indexed by key without subtracting low · case 03

Tables with a nonzero low bound select the wrong case or run off the operands.

Member previewVariant 3 · 3 implementations · 8 checks per implementation

Case contract

code is a method's bytes; at addr is tableswitch (0xAA) or lookupswitch (0xAB). After the opcode, 0-3 padding bytes align the next byte to a multiple of 4 from the method start; then big-endian signed 32-bit words: default, and either low, high and high-low+1 offsets, or npairs followed by sorted (match, offset) pairs. Branch offsets are relative to the switch opcode address. Return the target address, or ["VerifyError", reason] for low > high, negative npairs, keys not strictly increasing, another opcode, or truncated operands.

Why this case matters

Switch opcodes combine alignment, signed decoding and relative targets in one instruction.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
regression: tableswitch hit with aligned operands	`35`	`55`	Failed

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