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// Copyright (c) 2019-2021 Alexander Medvednikov. All rights reserved.
// Use of this source code is governed by an MIT license
// that can be found in the LICENSE file.
// This is a very basic crc32 implementation
// at the moment with no architecture optimizations
module crc32
// polynomials
pub const (
ieee = u32(0xedb88320)
castagnoli = u32(0x82f63b78)
koopman = u32(0xeb31d82e)
)
// The size of a CRC-32 checksum in bytes.
const (
size = 4
)
struct Crc32 {
mut:
table []u32
}
fn (mut c Crc32) generate_table(poly int) {
for i in 0 .. 256 {
mut crc := u32(i)
for _ in 0 .. 8 {
if crc & u32(1) == u32(1) {
crc = (crc >> 1) ^ u32(poly)
} else {
crc >>= u32(1)
}
}
c.table << crc
}
}
fn (c &Crc32) sum32(b []byte) u32 {
mut crc := ~u32(0)
for i in 0 .. b.len {
crc = c.table[byte(crc) ^ b[i]] ^ (crc >> 8)
}
return ~crc
}
pub fn (c &Crc32) checksum(b []byte) u32 {
return c.sum32(b)
}
// pass the polynomial to use
pub fn new(poly int) &Crc32 {
mut c := &Crc32{}
c.generate_table(poly)
return c
}
// calculate crc32 using ieee
pub fn sum(b []byte) u32 {
c := new(int(crc32.ieee))
return c.sum32(b)
}
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