chunkrs 0.9.0

//! FastCDC lookup tables.

/// Base gear hash table for FastCDC.
pub const GEAR_TABLE: [u64; 256] = [
    0x4d65822107fcfd52,
    0x78629a0f5f3f164f,
    0xd5104dc76695721d,
    0xb80704bb7b4d7c03,
    0x365a858149c6e2d1,
    0x57e9d1860d1d68d8,
    0x8866cb397916001e,
    0x9408d2ac22c4d294,
    0xc697f48392907a0,
    0xa68447a4189deb99,
    0x41f27cc6f3875d04,
    0x68255aaf95e94627,
    0x9b6cffa2ba517936,
    0x30b95ff183c471d4,
    0xa8b621587cb3ad0b,
    0x3c04951aa42655d9,
    0xa43a768b7c4e0b68,
    0xa5845c95d4491d1b,
    0x56ec3f2525632186,
    0x9bf98be2a9d78d73,
    0x1a02070f169c1121,
    0x2e3108dabb158644,
    0xc90bd268b68e6a3f,
    0x6e661e92759805f5,
    0xa584c47f2cdf5b8a,
    0x2606cd2b57d29245,
    0x6054502fc5d6d268,
    0x1a714cf86b83d0e2,
    0xeec34c367674cb74,
    0xd92e17f7b068d9db,
    0x430c8b35bb9457d8,
    0x39f6f78a15d523b,
    0x944419db794209ff,
    0x4dba7b0f9da1d7eb,
    0xfcd4b7a55a25e0cb,
    0x8a2b894cf840ec4b,
    0x4c22b02936d4ff9b,
    0x879143f7f4a5ee3b,
    0x589442fd5ad145f4,
    0x26984b92f6740304,
    0x962d968d3f71f8cb,
    0x4542c29291018d7c,
    0xc5a6e3cafccae224,
    0xa3a62343b186b51f,
    0xb629d9f17d9e8fbc,
    0xc3ea3b9393f93f33,
    0x207403def63a5b6f,
    0x241b3ae419476c36,
    0x64f1017fbc897d06,
    0x2e4fa459169873f5,
    0xf0b5a315724c7af1,
    0xa607c649581eeb39,
    0x727a71f52257bb7d,
    0xc7964976f269a28,
    0x7d0b9ca8be8e9981,
    0x89825e117039374b,
    0x9c73fac825416fed,
    0xd72d92faded7e411,
    0x1ee9f7676678e7aa,
    0xa7dff7ab244fcd36,
    0x7767830356aa6b86,
    0x5ef4e81ede4561ad,
    0x6688f8bd3e99b0a8,
    0x5d78399cbed80a3a,
    0x176a156ae58348b0,
    0xb6d467a4af63e58d,
    0xf2d0a1e9406aec9d,
    0x57613082c233f007,
    0xfd4d8e9fa5ead0bd,
    0x760b0d22050143a6,
    0xba08e4b738b6829,
    0xbf1f46e83699caf3,
    0x76a780ea967cd710,
    0x7a3ba6f606f665a6,
    0xac89c16725fd3d7f,
    0xd86d68260fd6e479,
    0x5aff01c926fbf29b,
    0x4829ee0716de4c35,
    0xd322787c2bf3394b,
    0x46a03cb44af864ba,
    0xe0bed31f1cb9e6c6,
    0xb3afd37941439089,
    0x90b92d0169a39144,
    0xfe34179dc34f182d,
    0xf2bb5389421657ff,
    0x293a0c2bf9fc6568,
    0x5c4e91e98b02c917,
    0x528047936c9c64b7,
    0xaf2560383d17909,
    0xd5b4a4b2ea3d4ca5,
    0xcfb58fbeaf635d47,
    0x2f5218587fc78769,
    0x9e503382be14186f,
    0x44841df33539b1ea,
    0x97f7ae24e9174548,
    0x1e925507c051e18a,
    0x5065855807b73658,
    0x103970a329ec300c,
    0xa402a18da250bf34,
    0x3485757ea7ed5d97,
    0xb7ab3641fe3dea79,
    0xd0031d27b8b352f7,
    0xc66b36dbc9b344e9,
    0x4fd269fd8e5f0475,
    0x5d55cb471941e52a,
    0xea4eef7a2694763d,
    0x8010d6326b40eabc,
    0xde377ef58485d68b,
    0xb332aafe336eacca,
    0x3fba24704399a363,
    0xcd4f278a67149b9c,
    0xb46e5f29ae10a901,
    0x83cc44bf5a5ffefb,
    0x803e6306563b26de,
    0x805d29286f00f02b,
    0x7539a2019f06397d,
    0xcb7fafc3545836c4,
    0xc79a2bf931d6416b,
    0xe85f325712f4128d,
    0xf062b076752f33ff,
    0xbaae3e3e4a305605,
    0x4cd239ea0c8dc214,
    0x835ca80d72521a90,
    0xec443faf8eb3e4a1,
    0x1ff5f26283efc6c6,
    0x5225fcd6090ec04f,
    0x1facfc5dc1540864,
    0x963a5aceec2c8aaa,
    0xcbdb185b70ab53ba,
    0xe83e14a538d3b494,
    0x58cfb024878d4063,
    0x3e19bf7a317ae3f,
    0xc504d6353cb62f07,
    0x7ce2e98ef360412c,
    0x601900fb4ffbf3a9,
    0xa5a1ffb522d554b4,
    0x606796b83f190476,
    0x1352ca320796a710,
    0x2d89c820f5c353cf,
    0x6a7cb5cf04f59bb7,
    0x9dac9b582d230176,
    0xd05ce263e2d6a9ce,
    0x3fcb626c3f1d7427,
    0xb7fbfbcafd915bb,
    0x83398e40b01aa47d,
    0x323423cfcde2c269,
    0xcb70e7ac7417bf38,
    0x76fd839a1e094f9a,
    0xc93a23eb55ece0ea,
    0x4b56783ccb94539b,
    0xb4b4a3c813d346b5,
    0x46baf44754e0c0c1,
    0x3eecfdbc6db30e37,
    0x7a9e3bdcdc02b390,
    0xe60aedf1a6e222f5,
    0xdbeaa0fe2f8c1fe,
    0xe43a7d712e166bdf,
    0x32560c7a67588a74,
    0x90b166a221898f34,
    0x1852fe624c330f1d,
    0x5eb29c7719af53ba,
    0x53b7a0ff70658b94,
    0x8c97d70a133c9673,
    0x429bd23a4efeeadd,
    0xcc3f10e0f212551,
    0x136f9ac7070f0914,
    0x89c09a3e6f241c57,
    0x2858bd10f13e41b7,
    0x146f70ff3be70cb0,
    0x91a39040f4b6f47f,
    0x294b4e8e20f31127,
    0xc50064ce6551cb89,
    0xc911aa87289cbd2c,
    0xc1a2d5288946f23d,
    0xd7930cf840a79c3b,
    0xd396d24a03c6d982,
    0xc322cee10365790c,
    0x53bf1faf0cf52517,
    0x5bb1f57b0bb131e8,
    0xd17d8ebf3da5475c,
    0x1a44786139efcca,
    0x83ed64e9bcd44eb4,
    0x8c8c4694a54af747,
    0xaf3f0d6fb73c32ed,
    0x69c93fb09f6c47ac,
    0xac80d58fe8ba8f22,
    0x2c1283b654043a66,
    0xa0624c583b0a7f20,
    0x1bb55397b4926431,
    0xc70a4f5ae17c02d5,
    0xb3770eb58f0d2558,
    0x40d4e552014fbff2,
    0x95974b9d7f803594,
    0x2a6a467079b76fbe,
    0xe9f98c4033fe2656,
    0xd9a30874792c8ee8,
    0x876a20af6b41292d,
    0x7fe4754afdff9c32,
    0xb4ad5ac882093298,
    0x8e4b5ac059483870,
    0xe3efbff5b2d5a113,
    0xbca82a42dd96e5a,
    0x6d8e96f5b8e56a9,
    0x5b7b2709ebd9dda9,
    0x2018fa6e04f9ce92,
    0xeca000e8cb440950,
    0xfca82947a67e52b1,
    0x1b35327a49f6d261,
    0x2c19e7792417fc3,
    0xf8fc24541c3b6bd9,
    0xbe67230b027b7e0,
    0xd2aaab031f765a41,
    0x27ebdd8f44c9ab40,
    0xb96747c045d99121,
    0xbe5ddb0efd7a84af,
    0xa8eb1ac99b75788,
    0xd5fe7f03e3abff4a,
    0xb3395eafa88aa67f,
    0xf33c374d736e41cc,
    0x7995c5dc9cbcbe5e,
    0xa8dfd8d37b3ccebc,
    0x3febdd25e1b7fa93,
    0xb3415dbd315ae6af,
    0x8289172b9cced2e2,
    0xd290a23119ea0f2f,
    0xb6df4331a9770722,
    0x2b77e80684a6bfdc,
    0xf197e13488f03f07,
    0x1e3ffa8aa44a03a4,
    0x61ebca0827a6b885,
    0x4939bb8b580c8ba,
    0xdd214064018153da,
    0xd01b6a22b648e604,
    0xc1acd9f551180278,
    0x8945fcdd893a310f,
    0xdcb389ac728f5f4c,
    0x709ec18437f5198b,
    0xfd275a873cc0ea9b,
    0xec7ae37ae39d02db,
    0x6a85764813883142,
    0x9fb95e8cca599392,
    0xf4ea42afc12d154e,
    0x99ad1bdc176163d,
    0xeae4ae6d5c92e2b8,
    0x508df0dcf9f95ede,
    0x60390908b802bdfc,
    0xd0e57d0f8a928585,
    0xc68571ddca6e10b,
    0x81e5dcfd887953e8,
    0x4abb18c948b9e962,
    0x88cd00c4e533e9a3,
    0x7fc76fad5e0ce6e5,
    0xd3189b251dba77ae,
    0x7e23bc6fc8214b8a,
    0xeadaea4753b428d7,
    0xaa80d0564cf20a65,
];

/// Pre-shifted gear table (each value << 1) for optimized hashing.
///
/// This is an optimization: instead of computing (hash >> 1) + gear,
/// we compute (hash >> 1) + (gear << 1), which is mathematically equivalent
/// but avoids the shift on the gear value during the hot loop.
///
/// The standard FastCDC uses: hash = (hash >> 1) + GEAR_TABLE[byte]
/// Our implementation uses: hash = (hash >> 1) + (GEAR_TABLE[byte] << 1)
///
/// This produces different hash values but maintains the same chunking behavior
/// because boundary detection depends on hash & mask, and the shift preserves
/// the relative distribution of hash values.
pub const GEAR_TABLE_SHIFTED: [u64; 256] = {
    let mut shifted = [0u64; 256];
    let mut i = 0u32;
    while i < 256 {
        shifted[i as usize] = GEAR_TABLE[i as usize].wrapping_shl(1);
        i += 1;
    }
    shifted
};

/// Pre-computed zero-padded masks for FastCDC.
///
/// Indexed by log2(chunk_size), i.e., MASKS[13] is for 8KB chunks (2^13).
pub const MASKS: [u64; 32] = [
    0x0000_0000_0000_0000, // 2^0
    0x0000_0000_0000_0001, // 2^1
    0x0000_0000_0000_0003, // 2^2
    0x0000_0000_0000_0007, // 2^3
    0x0000_0000_0000_000f, // 2^4
    0x0000_0000_0000_001f, // 2^5
    0x0000_0000_0000_003f, // 2^6
    0x0000_0000_0000_007f, // 2^7
    0x0000_0000_0000_00ff, // 2^8
    0x0000_0000_0000_01ff, // 2^9
    0x0000_0000_0000_03ff, // 2^10
    0x0000_0000_0000_07ff, // 2^11
    0x0000_0000_0000_0fff, // 2^12
    0x0000_0000_d903_0353, // 2^13 (8KB)
    0x0000_0001_b207_06a7, // 2^14 (16KB)
    0x0000_0000_3590_7035, // 2^15 (32KB)
    0x0000_0006_b20e_e06a, // 2^16 (64KB)
    0x0000_0000_d903_0353, // 2^17 (128KB)
    0x0000_0001_b207_06a7, // 2^18 (256KB)
    0x0000_0000_3590_7035, // 2^19 (512KB)
    0x0000_0006_b20e_e06a, // 2^20 (1MB)
    0x0000_0000_d903_0353, // 2^21 (2MB)
    0x0000_0001_b207_06a7, // 2^22 (4MB)
    0x0000_0000_3590_7035, // 2^23 (8MB)
    0x0000_0006_b20e_e06a, // 2^24 (16MB)
    0x0000_0000_d903_0353, // 2^25 (32MB)
    0x0000_0001_b207_06a7, // 2^26 (64MB)
    0x0000_0000_3590_7035, // 2^27 (128MB)
    0x0000_0006_b20e_e06a, // 2^28 (256MB)
    0x0000_0000_d903_0353, // 2^29 (512MB)
    0x0000_0001_b207_06a7, // 2^30 (1GB)
    0x0000_0000_3590_7035, // 2^31 (2GB)
];

/// Generates a keyed gear table using BLAKE3 (requires `keyed-cdc` feature).
#[cfg(feature = "keyed-cdc")]
pub fn generate_keyed_gear_table(key: [u8; 32]) -> [u64; 256] {
    use blake3::Hasher;

    let mut keyed = [0u64; 256];
    for i in 0..256 {
        let mut hasher = Hasher::new_keyed(&key);
        hasher.update(&GEAR_TABLE[i].to_le_bytes());
        let hash = hasher.finalize();
        keyed[i] = u64::from_le_bytes(hash.as_bytes()[0..8].try_into().unwrap());
    }
    keyed
}

/// Generates a pre-shifted keyed gear table (requires `keyed-cdc` feature).
#[cfg(feature = "keyed-cdc")]
pub fn generate_keyed_gear_table_shifted(key: [u8; 32]) -> [u64; 256] {
    let keyed = generate_keyed_gear_table(key);
    let mut shifted = [0u64; 256];
    for i in 0..256 {
        shifted[i] = keyed[i].wrapping_shl(1);
    }
    shifted
}