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use std::hash::Hasher;
pub const ECMA: u64 = 0xc96c5795d7870f42;
pub const ISO: u64 = 0xd800000000000000;
lazy_static! {
pub static ref ECMA_TABLE: [u64; 256] = make_table(ECMA);
pub static ref ISO_TABLE: [u64; 256] = make_table(ISO);
}
pub struct Digest {
table: [u64; 256],
initial: u64,
value: u64
}
pub trait Hasher64 {
fn reset(&mut self);
fn write(&mut self, bytes: &[u8]);
fn sum64(&self) -> u64;
}
pub fn make_table(poly: u64) -> [u64; 256] {
let mut table = [0u64; 256];
for i in 0..256 {
let mut value = i as u64;
for _ in 0..8 {
value = if (value & 1) == 1 {
(value >> 1) ^ poly
} else {
value >> 1
}
}
table[i] = value;
}
table
}
pub fn update(mut value: u64, table: &[u64; 256], bytes: &[u8]) -> u64 {
value = !value;
for &i in bytes.iter() {
value = table[((value as u8) ^ i) as usize] ^ (value >> 8)
}
!value
}
pub fn checksum_ecma(bytes: &[u8]) -> u64 {
return update(0, &ECMA_TABLE, bytes);
}
pub fn checksum_iso(bytes: &[u8]) -> u64 {
return update(0, &ISO_TABLE, bytes);
}
impl Digest {
pub fn new(poly: u64) -> Digest {
Digest {
table: make_table(poly),
initial: 0,
value: 0
}
}
pub fn new_with_initial(poly: u64, initial: u64) -> Digest {
Digest {
table: make_table(poly),
initial: initial,
value: initial
}
}
}
impl Hasher64 for Digest {
fn reset(&mut self) {
self.value = self.initial;
}
fn write(&mut self, bytes: &[u8]) {
self.value = update(self.value, &self.table, bytes);
}
fn sum64(&self) -> u64 {
self.value
}
}
impl Hasher for Digest {
fn write(&mut self, bytes: &[u8]) {
Hasher64::write(self, bytes);
}
fn finish(&self) -> u64 {
self.sum64()
}
}