mirror of https://bitbucket.org/ausocean/av.git
73 lines
1.7 KiB
Go
73 lines
1.7 KiB
Go
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/*
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NAME
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crc.go
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DESCRIPTION
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See Readme.md
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AUTHOR
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Saxon Milton <saxon@ausocean.org>
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LICENSE
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crc.go is Copyright (C) 2018 the Australian Ocean Lab (AusOcean)
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It is free software: you can redistribute it and/or modify them
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under the terms of the GNU General Public License as published by the
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Free Software Foundation, either version 3 of the License, or (at your
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option) any later version.
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It is distributed in the hope that it will be useful, but WITHOUT
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ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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for more details.
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You should have received a copy of the GNU General Public License
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along with revid in gpl.txt. If not, see http://www.gnu.org/licenses.
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*/
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package psi
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import (
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"hash/crc32"
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"math/bits"
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)
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// addCrc appends a crc table to a given psi table in bytes
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func addCrc(out []byte) []byte {
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out = append(out, make([]byte, 4)...)
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out = updateCrc(out)
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return out
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}
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// updateCrc updates the crc of psi bytes slice that may have been modified
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func updateCrc(out []byte) []byte {
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crc32 := crc32_Update(0xffffffff, crc32_MakeTable(bits.Reverse32(crc32.IEEE)), out[1:len(out)-4])
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out[len(out)-4] = byte(crc32 >> 24)
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out[len(out)-3] = byte(crc32 >> 16)
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out[len(out)-2] = byte(crc32 >> 8)
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out[len(out)-1] = byte(crc32)
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return out
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}
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func crc32_MakeTable(poly uint32) *crc32.Table {
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var t crc32.Table
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for i := range t {
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crc := uint32(i) << 24
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for j := 0; j < 8; j++ {
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if crc&0x80000000 != 0 {
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crc = (crc << 1) ^ poly
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} else {
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crc <<= 1
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}
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}
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t[i] = crc
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}
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return &t
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}
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func crc32_Update(crc uint32, tab *crc32.Table, p []byte) uint32 {
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for _, v := range p {
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crc = tab[byte(crc>>24)^v] ^ (crc << 8)
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}
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return crc
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}
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