test(rust): Add Rust <-> C++ differential decoder fuzzer by CommanderStorm · Pull Request #1471 · maplibre/maplibre-tile-spec

CommanderStorm · 2026-06-24T15:12:11Z

a diff fuzzer for rust and cpp.

Currently not wired into CI, because it finds issues 🎉

Clarify support for plain integer streams #1137

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Removed comments related to the differential fuzzer and its usage.

github-actions · 2026-06-24T15:22:02Z

Performance Comparison

Performance Comparison `main` → `differential-fuzzer`

Total Elapsed Time: 2.39s → 2.33s (-2.6%)
CPU Baseline: 82.53µs → 81.47µs (-1.3%)
Benchmark ID: mlt-convert

timing - Function execution time metrics.

+--------------------------------------+------------------------------+--------------------------------+--------------------------------+--------------------------------+------------------------------+
| Function                             | Calls                        | Avg                            | P95                            | Total                          | % Total                      |
+--------------------------------------+------------------------------+--------------------------------+--------------------------------+--------------------------------+------------------------------+
| optimizer::encode                    | 14092 → 14092 (+0.0%)        | 566.65µs → 552.38µs (-2.5%)    | 2.48ms → 2.32ms (-6.5%)        | 7.99s → 7.78s (-2.6%)          | 333.69% → 333.97% (+0.1%)    |
+--------------------------------------+------------------------------+--------------------------------+--------------------------------+--------------------------------+------------------------------+
| optimizer::encode_into               | 28188 → 28188 (+0.0%)        | 179.66µs → 175.03µs (-2.6%)    | 786.43µs → 778.75µs (-1.0%)    | 5.06s → 4.93s (-2.6%)          | 211.63% → 211.67% (+0.0%)    |
+--------------------------------------+------------------------------+--------------------------------+--------------------------------+--------------------------------+------------------------------+
| encode::write_to                     | 28190 → 28192 (+0.0%)        | 139.41µs → 135.91µs (-2.5%)    | 681.98µs → 676.86µs (-0.8%)    | 3.93s → 3.83s (-2.5%)          | 164.23% → 164.39% (+0.1%)    |
+--------------------------------------+------------------------------+--------------------------------+--------------------------------+--------------------------------+------------------------------+
| writer::with                         | 2197192 → 2197152 (-0.0%)    | 1.28µs → 1.25µs (-2.3%)        | 1.69µs → 1.68µs (-0.6%)        | 2.81s → 2.74s (-2.5%)          | 117.42% → 117.58% (+0.1%)    |
+--------------------------------------+------------------------------+--------------------------------+--------------------------------+--------------------------------+------------------------------+
| mlt::main                            | 1 → 1 (+0.0%)                | 2.39s → 2.33s (-2.5%)          | 2.39s → 2.33s (-2.5%)          | 2.39s → 2.33s (-2.5%)          | 100.00% → 100.00% (+0.0%)    |
+--------------------------------------+------------------------------+--------------------------------+--------------------------------+--------------------------------+------------------------------+
| optimizer::analyze                   | 14096 → 14096 (+0.0%)        | 134.85µs → 131.37µs (-2.6%)    | 699.90µs → 704.51µs (+0.7%)    | 1.90s → 1.85s (-2.6%)          | 79.44% → 79.45% (+0.0%)      |
+--------------------------------------+------------------------------+--------------------------------+--------------------------------+--------------------------------+------------------------------+
| shared_dict::group_string_properties | 14096 → 14096 (+0.0%)        | 130.00µs → 126.54µs (-2.7%)    | 681.47µs → 678.40µs (-0.5%)    | 1.83s → 1.78s (-2.7%)          | 76.58% → 76.53% (-0.1%)      |
+--------------------------------------+------------------------------+--------------------------------+--------------------------------+--------------------------------+------------------------------+
| encode::dict_may_be_beneficial       | 28190 → 28192 (+0.0%)        | 49.62µs → 48.14µs (-3.0%)      | 223.23µs → 223.87µs (+0.3%)    | 1.40s → 1.36s (-2.9%)          | 58.46% → 58.23% (-0.4%)      |
+--------------------------------------+------------------------------+--------------------------------+--------------------------------+--------------------------------+------------------------------+
| encode::write_properties             | 28188 → 28188 (+0.0%)        | 37.51µs → 36.33µs (-3.1%)      | 143.23µs → 142.21µs (-0.7%)    | 1.06s → 1.02s (-3.8%)          | 44.18% → 43.93% (-0.6%)      |
+--------------------------------------+------------------------------+--------------------------------+--------------------------------+--------------------------------+------------------------------+
| encode::write_prop                   | 116566 → 116564 (-0.0%)      | 8.99µs → 8.69µs (-3.3%)        | 18.08µs → 18.13µs (+0.3%)      | 1.05s → 1.01s (-3.8%)          | 43.77% → 43.45% (-0.7%)      |
+--------------------------------------+------------------------------+--------------------------------+--------------------------------+--------------------------------+------------------------------+
| shared_dict::write_shared_dict       | 24001 → 24000 (-0.0%)        | 26.59µs → 25.75µs (-3.2%)      | 54.69µs → 54.21µs (-0.9%)      | 638.27ms → 618.07ms (-3.2%)    | 26.67% → 26.52% (-0.6%)      |
+--------------------------------------+------------------------------+--------------------------------+--------------------------------+--------------------------------+------------------------------+
| tile::from_tile                      | 28192 → 28192 (+0.0%)        | 20.95µs → 20.59µs (-1.7%)      | 88.51µs → 86.72µs (-2.0%)      | 590.48ms → 580.35ms (-1.7%)    | 24.68% → 24.90% (+0.9%)      |
+--------------------------------------+------------------------------+--------------------------------+--------------------------------+--------------------------------+------------------------------+
| strings::write_str_col               | 57067 → 57064 (-0.0%)        | 6.12µs → 5.92µs (-3.3%)        | 11.54µs → 11.52µs (-0.2%)      | 349.45ms → 338.08ms (-3.3%)    | 14.60% → 14.50% (-0.7%)      |
+--------------------------------------+------------------------------+--------------------------------+--------------------------------+--------------------------------+------------------------------+
| sort::curve_params                   | 14096 → 14096 (+0.0%)        | 17.30µs → 16.95µs (-2.0%)      | 77.25µs → 76.93µs (-0.4%)      | 243.89ms → 238.98ms (-2.0%)    | 10.19% → 10.25% (+0.6%)      |
+--------------------------------------+------------------------------+--------------------------------+--------------------------------+--------------------------------+------------------------------+
| strings::fsst_try_train              | 40536 → 40536 (+0.0%)        | 5.08µs → 4.95µs (-2.6%)        | 71.00ns → 71.00ns (+0.0%)      | 206.07ms → 200.83ms (-2.5%)    | 8.61% → 8.62% (+0.1%)        |
+--------------------------------------+------------------------------+--------------------------------+--------------------------------+--------------------------------+------------------------------+

alloc-bytes - Exclusive allocation bytes by each function (excluding nested calls).

+--------------------------------------+------------------------------+------------------------------+--------------------------------+--------------------------------+----------------------------+
| Function                             | Calls                        | Avg                          | P95                            | Total                          | % Total                    |
+--------------------------------------+------------------------------+------------------------------+--------------------------------+--------------------------------+----------------------------+
| tile::from_tile                      | 28192 → 28192 (+0.0%)        | 44.2 KB → 44.2 KB (+0.0%)    | 239.2 KB → 239.2 KB (+0.0%)    | 1.2 GB → 1.2 GB (+0.0%)        | 24.43% → 24.43% (+0.0%)    |
+--------------------------------------+------------------------------+------------------------------+--------------------------------+--------------------------------+----------------------------+
| optimizer::encode                    | 14092 → 14092 (+0.0%)        | 86.2 KB → 86.2 KB (+0.0%)    | 159.2 KB → 159.2 KB (+0.0%)    | 1.2 GB → 1.2 GB (+0.0%)        | 23.84% → 23.84% (+0.0%)    |
+--------------------------------------+------------------------------+------------------------------+--------------------------------+--------------------------------+----------------------------+
| writer::with                         | 2197192 → 2197152 (-0.0%)    | 518 B → 518 B (+0.0%)        | 20.3 KB → 20.3 KB (+0.0%)      | 1.1 GB → 1.1 GB (+0.0%)        | 21.84% → 21.84% (+0.0%)    |
+--------------------------------------+------------------------------+------------------------------+--------------------------------+--------------------------------+----------------------------+
| strings::fsst_try_train              | 40536 → 40536 (+0.0%)        | 16.8 KB → 16.8 KB (+0.0%)    | 3.6 MB → 3.6 MB (+0.0%)        | 664.5 MB → 664.5 MB (+0.0%)    | 13.35% → 13.35% (+0.0%)    |
+--------------------------------------+------------------------------+------------------------------+--------------------------------+--------------------------------+----------------------------+
| shared_dict::group_string_properties | 14096 → 14096 (+0.0%)        | 30.1 KB → 30.1 KB (+0.0%)    | 167.5 KB → 167.5 KB (+0.0%)    | 414.1 MB → 414.1 MB (+0.0%)    | 8.32% → 8.32% (+0.0%)      |
+--------------------------------------+------------------------------+------------------------------+--------------------------------+--------------------------------+----------------------------+
| encode::write_to                     | 28190 → 28192 (+0.0%)        | 7.4 KB → 7.4 KB (+0.0%)      | 35.7 KB → 35.7 KB (+0.0%)      | 204.9 MB → 204.9 MB (+0.0%)    | 4.12% → 4.12% (+0.0%)      |
+--------------------------------------+------------------------------+------------------------------+--------------------------------+--------------------------------+----------------------------+
| shared_dict::write_shared_dict       | 24001 → 24000 (-0.0%)        | 3.4 KB → 3.4 KB (+0.0%)      | 11.5 KB → 11.5 KB (+0.0%)      | 80.2 MB → 80.2 MB (+0.0%)      | 1.61% → 1.61% (+0.0%)      |
+--------------------------------------+------------------------------+------------------------------+--------------------------------+--------------------------------+----------------------------+
| strings::write_str_col               | 57067 → 57064 (-0.0%)        | 893 B → 893 B (+0.0%)        | 3.5 KB → 3.5 KB (+0.0%)        | 48.6 MB → 48.6 MB (+0.0%)      | 0.98% → 0.98% (+0.0%)      |
+--------------------------------------+------------------------------+------------------------------+--------------------------------+--------------------------------+----------------------------+
| encode::build_morton_dict            | 362 → 362 (+0.0%)            | 44.6 KB → 44.6 KB (+0.0%)    | 89.9 KB → 89.9 KB (+0.0%)      | 15.8 MB → 15.8 MB (+0.0%)      | 0.32% → 0.32% (+0.0%)      |
+--------------------------------------+------------------------------+------------------------------+--------------------------------+--------------------------------+----------------------------+
| strings::write_raw_str_data          | 137740 → 137731 (-0.0%)      | 117 B → 117 B (+0.0%)        | 10.8 KB → 10.8 KB (+0.0%)      | 15.4 MB → 15.4 MB (+0.0%)      | 0.31% → 0.31% (+0.0%)      |
+--------------------------------------+------------------------------+------------------------------+--------------------------------+--------------------------------+----------------------------+
| optimizer::analyze                   | 14096 → 14096 (+0.0%)        | 1.0 KB → 1.0 KB (+0.0%)      | 6.5 KB → 6.5 KB (+0.0%)        | 14.0 MB → 14.0 MB (+0.0%)      | 0.28% → 0.28% (+0.0%)      |
+--------------------------------------+------------------------------+------------------------------+--------------------------------+--------------------------------+----------------------------+
| encode::build_hilbert_dict           | 362 → 362 (+0.0%)            | 25.9 KB → 25.9 KB (+0.0%)    | 90.7 KB → 90.7 KB (+0.0%)      | 9.2 MB → 9.2 MB (+0.0%)        | 0.18% → 0.18% (+0.0%)      |
+--------------------------------------+------------------------------+------------------------------+--------------------------------+--------------------------------+----------------------------+
| encode::dict_may_be_beneficial       | 28190 → 28192 (+0.0%)        | 256 B → 256 B (+0.0%)        | 256 B → 256 B (+0.0%)          | 6.9 MB → 6.9 MB (+0.0%)        | 0.14% → 0.14% (+0.0%)      |
+--------------------------------------+------------------------------+------------------------------+--------------------------------+--------------------------------+----------------------------+
| encode::write_prop                   | 116566 → 116564 (-0.0%)      | 41 B → 41 B (+0.0%)          | 400 B → 400 B (+0.0%)          | 4.6 MB → 4.6 MB (+0.0%)        | 0.09% → 0.09% (+0.0%)      |
+--------------------------------------+------------------------------+------------------------------+--------------------------------+--------------------------------+----------------------------+
| strings::write_str_plain             | 57068 → 57065 (-0.0%)        | 69 B → 69 B (+0.0%)          | 240 B → 240 B (+0.0%)          | 3.8 MB → 3.8 MB (+0.0%)        | 0.08% → 0.08% (+0.0%)      |
+--------------------------------------+------------------------------+------------------------------+--------------------------------+--------------------------------+----------------------------+

Threads

No threads to compare

Generated with hotpath-rs

Per-tile encoded size diff

zoom	tiles	prev_total	curr_total
0	1	71471	71471
1	4	220990	220990
2	16	615018	615018
3	64	1653881	1653881
4	256	3828995	3828995
5	1024	9716961	9716961
6	4096	32402309	32402309
ALL	5461	48509625	48509625

Top 3 improvements

Top 3 degradations

codecov-commenter · 2026-06-24T15:45:00Z

Codecov Report

❌ Patch coverage is 0% with 10 lines in your changes missing coverage. Please review.
✅ Project coverage is 62.78%. Comparing base (a35ba6d) to head (313d642).

Files with missing lines	Patch %	Lines
rust/mlt-core/src/encoder/fuzzing.rs	0.00%	10 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #1471       +/-   ##
===========================================
- Coverage   95.78%   62.78%   -33.00%     
===========================================
  Files          68       94       +26     
  Lines        4908    15327    +10419     
  Branches      760        0      -760     
===========================================
+ Hits         4701     9623     +4922     
- Misses        192     5704     +5512     
+ Partials       15        0       -15

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Copilot AI review requested due to automatic review settings June 24, 2026 15:12

Copilot AI reviewed Jun 24, 2026

CommanderStorm changed the title ~~Add Rust↔C++ differential decoder fuzzer~~ Add Rust <-> C++ differential decoder fuzzer Jun 24, 2026

Remove comments about differential fuzzer in Cargo.toml

8681842

Removed comments related to the differential fuzzer and its usage.

CommanderStorm changed the title ~~Add Rust <-> C++ differential decoder fuzzer~~ test(rust): Add Rust <-> C++ differential decoder fuzzer Jun 24, 2026

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313d642

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test(rust): Add Rust <-> C++ differential decoder fuzzer#1471

test(rust): Add Rust <-> C++ differential decoder fuzzer#1471
CommanderStorm wants to merge 3 commits into
maplibre:mainfrom
CommanderStorm:differential-fuzzer

CommanderStorm commented Jun 24, 2026 •

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Performance Comparison `main` → `differential-fuzzer`

timing - Function execution time metrics.

alloc-bytes - Exclusive allocation bytes by each function (excluding nested calls).

Threads

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Top 3 degradations

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Performance Comparison main → differential-fuzzer

timing - Function execution time metrics.

alloc-bytes - Exclusive allocation bytes by each function (excluding nested calls).

Threads

Top 3 improvements

Top 3 degradations

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codecov-commenter commented Jun 24, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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CommanderStorm commented Jun 24, 2026 •

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github-actions Bot commented Jun 24, 2026 •

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Performance Comparison `main` → `differential-fuzzer`

codecov-commenter commented Jun 24, 2026 •

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