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//! RDB DUMP/RESTORE 校验和（对标 libs/common/Crc64.cs，移植 redis crc64）
/// libs/common/Crc64.cs:POLY
///
/// Polynomial (same as redis)
const POLY: u64 = 0xad93d23594c935a9;
/// libs/common/Crc64.cs:Reflect64
///
/// Reverse all bits in a 64-bit value (bit reflection)
#[inline]
const fn reflect64(mut data: u64) -> u64 {
// swap odd/even bits
data = ((data >> 1) & 0x5555555555555555) | ((data & 0x5555555555555555) << 1);
// swap consecutive pairs
data = ((data >> 2) & 0x3333333333333333) | ((data & 0x3333333333333333) << 2);
// swap nibbles
data = ((data >> 4) & 0x0F0F0F0F0F0F0F0F) | ((data & 0x0F0F0F0F0F0F0F0F) << 4);
// swap bytes, then 2-byte pairs, then 4-byte pairs
data.swap_bytes()
}
/// libs/common/Crc64.cs:Crc64Bitwise
///
/// A direct bit-by-bit CRC64 calculation (like _crc64 in C)
fn crc64_bitwise(data: &[u8]) -> u64 {
let mut crc: u64 = 0;
for &c in data {
let mut i: u8 = 1;
while i != 0 {
// interpret the top bit of 'crc' and current bit of 'c'
let mut bit_set = (crc & 0x8000000000000000) != 0;
let c_bit = (c & i) != 0;
// if cbit flips the sense, invert bitSet
if c_bit {
bit_set = !bit_set;
}
// shift
crc <<= 1;
// apply polynomial if needed
if bit_set {
crc ^= POLY;
}
i <<= 1;
}
}
// reflect and XOR, per standard
reflect64(crc)
}
/// libs/common/Crc64.cs:Hash
///
/// Computes crc64（小端 8 字节输出，与 C# BitConverter.GetBytes 一致）
pub fn hash(data: &[u8]) -> [u8; 8] {
crc64_bitwise(data).to_le_bytes()
}
#[cfg(test)]
mod tests {
use super::{crc64_bitwise, hash};
#[test]
fn empty_and_properties() {
// 空输入：crc=0，reflect 后仍为 0
assert_eq!(hash(b""), [0u8; 8]);
// 确定性 + 长度敏感性
assert_eq!(hash(b"abc"), hash(b"abc"));
assert_ne!(hash(b"abc"), hash(b"abd"));
assert_ne!(hash(b"a"), hash(b"aa"));
}
#[test]
fn little_endian_output_matches_bitwise() {
// Hash 输出为位运算结果的小端 8 字节
let data = b"123456789";
let le = crc64_bitwise(data).to_le_bytes();
assert_eq!(hash(data), le);
}
}