Example of Fletcher16 (Fletcher's checksum) in Go package main
import "fmt"
// Fletcher16 returns the checksum of the data using the Fletcher's
// checksum algorithm.
func Fletcher16 (data []byte ) uint16 {
sum1 := uint16 (0 )
sum2 := uint16 (0 )
for _ , char := range data {
sum1 = (sum1 + uint16 (char )) % 0xff
sum2 = (sum2 + sum1 ) % 0xff
}
return (sum2 << 8 ) | sum1
}
// IsValidFletcher16 returns true if the given checkSum is a valid check
// sum of the data.
func IsValidFletcher16 (data []byte , checkSum uint16 ) bool {
// Calculate check bytes from the checksum
f0 := uint8 (checkSum & 0xff )
f1 := uint8 ((checkSum >> 8 ) & 0xff )
c0 := 0xff - ((f0 + f1 ) % 0xff )
c1 := 0xff - ((f0 + c0 ) % 0xff )
return Fletcher16 (append (data , c0 , c1 )) == 0
}
func Example () {
for _ , input := range [][]byte {
[]byte ("abcdef" ),
[]byte {0x01 , 0x02 },
[]byte {0x01 , 0x02 , 0x03 , 0x04 },
} {
checkSum := Fletcher16 (input )
isValid := IsValidFletcher16 (input , checkSum )
fmt .Printf ("Input: %#v\n \t -> Check SUM: 0x%04x, Verify: %v\n " ,
string (input ),
checkSum ,
isValid ,
)
}
// Output:
// Input: "abcdef"
// -> Check SUM: 0x2057, Verify: true
// Input: "\x01\x02"
// -> Check SUM: 0x0403, Verify: true
// Input: "\x01\x02\x03\x04"
// -> Check SUM: 0x140a, Verify: true
}