v/vlib/hash/crc32/crc32.v

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// 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 (
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ieee = 0xedb88320
castagnoli = 0x82f63b78
koopman = 0xeb31d82e
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)
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// The size of a CRC-32 checksum in bytes.
const (
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size = 4
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)
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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 = (crc >> 1) ^ u32(poly)
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} else {
crc >>= u32(1)
}
}
c.table << crc
}
}
fn(c &Crc32) sum32(b []byte) u32 {
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mut crc := ~u32(0)
for i := 0; i < b.len; i++ {
crc = c.table[byte(crc)^b[i]] ^ u32(crc >> u32(8))
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}
return ~crc
}
pub fn(c &Crc32) checksum(b []byte) u32 {
return c.sum32(b)
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}
// pass the polinomial to use
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pub fn new(poly int) &Crc32 {
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mut c := &Crc32{}
c.generate_table(poly)
return c
}
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// calculate crc32 using ieee
pub fn sum(b []byte) u32 {
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mut c := new(ieee)
return c.sum32(b)
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}