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cksum.go
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cksum.go
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// Copyright 2018 the u-root Authors. All rights reserved
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package main
import (
"fmt"
"hash/crc32"
"io/ioutil"
"os"
"github.com/spf13/pflag"
)
func reverse(x uint32) uint32 {
x = (((x & 0xaaaaaaaa) >> 1) | ((x & 0x55555555) << 1))
x = (((x & 0xcccccccc) >> 2) | ((x & 0x33333333) << 2))
x = (((x & 0xf0f0f0f0) >> 4) | ((x & 0x0f0f0f0f) << 4))
x = (((x & 0xff00ff00) >> 8) | ((x & 0x00ff00ff) << 8))
return ((x >> 16) | (x << 16))
}
func reverseByte(b byte) byte {
b = (b&0xF0)>>4 | (b&0x0F)<<4
b = (b&0xCC)>>2 | (b&0x33)<<2
b = (b&0xAA)>>1 | (b&0x55)<<1
return b
}
func reverseBytes(b []byte) []byte {
for i := range b {
b[i] = reverseByte(b[i])
}
return b
}
func helpPrinter() {
fmt.Printf("Usage:\ncksum <File Name>\n")
pflag.PrintDefaults()
os.Exit(0)
}
func versionPrinter() {
fmt.Println("cksum utility, URoot Version.")
os.Exit(0)
}
func getInput(fileName string) (input []byte, err error) {
if fileName != "" {
return ioutil.ReadFile(fileName)
}
return ioutil.ReadAll(os.Stdin)
}
func appendLengthToData(data []byte) []byte {
length := len(data)
for length > 0 {
data = append(data, byte(length))
length = (length >> 8)
}
return data
}
func calculateCksum(data []byte) uint32 {
return reverse(crc32.Update(0xffffffff, crc32.MakeTable(0xEDB88320), reverseBytes(appendLengthToData(data))))
}
func main() {
var (
help bool
version bool
)
cliArgs := ""
pflag.BoolVarP(&help, "help", "h", false, "Show this help and exit")
pflag.BoolVarP(&version, "version", "v", false, "Print Version")
pflag.Parse()
if help {
helpPrinter()
}
if version {
versionPrinter()
}
if len(os.Args) >= 2 {
cliArgs = os.Args[1]
}
input, err := getInput(cliArgs)
if err != nil {
return
}
fmt.Println(calculateCksum(input), len(input), cliArgs)
}