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WebAssembly · 26 Boundary-value Correctness
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Stage: Correctness and Bottleneck Evaluation · External example · preview instructions · Storage ID: webassembly-step-26
Goals and learning outcomes
- Learning outcome: explain the role of Correctness first. Input cases: arrays of length 0·1·1003.
- Deliverable: PASS or failure differences for each case. Explain the rationale for handling Error tolerance, linking it to the code.
Prerequisites
Prepare the experiment results for Kernel time and Total cost from Unit 25, “Total Cost Including Copies”.
Key concepts and explanations
Correctness first
Output contracts must match before comparing performance. Decide whether empty arrays and negative values are within the supported range.
Error tolerance
Match bit widths for integers and define tolerance for floating-point values. Do not hide bugs with arbitrary tolerances.
Practice setup
First check the execution scope guidance on the example screen. The following describes the environment needed to extend the assignment in a separate project. The iframe preview is an experiment with WebAssembly.Memory and JS reference computations; do not present it as execution of an actual Wasm module. Practice with actual modules in a separate Node 22+ environment or a controlled local web project. Use kernel.wat·kernel.wasm·benchmark.mjs in the existing src/labs/webassembly-02·03 folders, and rebuild with the official wat2wasm tool when modifying WAT. Preserve CSP·isolation, and record measurements yourself.
The linked example is a starting point. It does not implement every task below. Complete work beyond its supported scope in a separate project.
Practice tasks
- In day-26.mjs in a separate practice project, use node:assert to compare empty·single-element·boundary-length·negative inputs against the JS reference. Refer to the existing Unit 1·14·28 examples only as starting points.
- Input conditions: arrays of length 0·1·1003. Baseline: small integers. Run under the baseline conditions, then record observations and errors in notes/day-26.md.
- Variable: data; changed value: boundary integers. Run again through the same input path. Deliverable to save: PASS or failure differences for each case. Hypothesis to check: Cases where numeric contracts disagree are exposed. Compare it with the actual results, and record whether they agree and why they differ.
Variables to observe
| Variable | Baseline | Change | Expected change / hypothesis |
|---|---|---|---|
| data | small integers | boundary integers | Cases where numeric contracts disagree are exposed. |
Predictions in this table are not measured results. Change one condition at a time and record why the actual result differs.
Completion criteria
- Required deliverable: PASS or failure differences for each case. Results are available for both the baseline and changed conditions, allowing comparison of 2 conditions; input values and the execution environment are recorded together.
- The explanation of differences between the two conditions connects both concepts: Correctness first and Error tolerance. For unexpected items, at least 1 cause or reason they remain unresolved is recorded.
Self-check
- Which processing stage does Correctness first affect in this exercise? Input cases: arrays of length 0·1·1003.
- Variable: data. Hypothesis to check: Cases where numeric contracts disagree are exposed. Did the actual results agree with the hypothesis? Explain the evidence in terms of Error tolerance.
Official references
Linked example and execution scope
Example source · Runtime environments and limits
Standalone WAT + Node assertions; iframe CSP blocks Wasm compilation.
Source code and records are not overwritten automatically. Resetting an existing example also preserves your notes.
Next learning
Previous: Total Cost Including Copies · Next: Environment and Adoption Criteria