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v/vlib/hash/crc32/crc32.v

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2019-07-13 16:11:32 +03:00
// Copyright (c) 2019 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
const (
IEEE = 0xedb88320
Castagnoli = 0x82f63b78
Koopman = 0xeb31d82e
)
struct Crc32 {
mut:
table []u32
}
fn(c mut Crc32) generate_table(poly int) {
for i := 0; i < 256; i++ {
mut crc := u32(i)
for j := 0; j < 8; j++ {
if crc&u32(1) == u32(1) {
crc = u32((crc >> u32(1)) ^ poly)
} else {
crc >>= u32(1)
}
}
c.table << crc
}
}
fn(c &Crc32) sum_32(s string) u32 {
mut crc := ~u32(0)
for i := 0; i < s.len; i++ {
crc = c.table[byte(crc)^s[i]] ^ u32(crc >> u32(8))
}
return ~crc
}
pub fn(c &Crc32) checksum(s string) u32 {
return c.sum_32(s)
}
// pass the polinomial to use
pub fn new(poly int) *Crc32 {
mut c := &Crc32{}
c.generate_table(poly)
return c
}
// calculate crc32 using IEEE
pub fn sum(s string) u32 {
mut c := new(IEEE)
return c.sum_32(s)
}