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