shred: residual-entropy scheduling for --random-source

[sankalpsthakur]

Summary

Depends on #13699 (genpattern) which depends on #13694 (patterns).

Implement residual-byte integer generation (FilePassRng) so choose() over a given byte stream matches GNU pass order. Both default and --random-source paths use genpattern. Deletes create_test_compatible_sequence.

Clean-room residual scheme matching public randint residual behavior / observed gshred 9.11; not a GPL port.

Fixes #11611

Tests

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

• n=20 exact sequence with 0x55 source
• distribution matrix: n in {25,50,60,100,500,1000}
• file-source scheduling (non-WASI)

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

[codspeed-hq]

Merging this PR will improve performance by 3.03%

⚡ 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-random-source (b3a6612) 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