将简单的哈希函数从c转换为go

Question

I'm trying to to convert a simple hash-function from C to Go.

What is the difference between these C and Go scripts and how do I fix the Go code?

C -> Results in {FB;01;4C|64:KDY;KMT;KYR;KT0;TKK;PAC;UD01;UD02;UD03;ID01;ID02;ID03;SYS|124A}

int   sum;
char* pChar;
char  s[8];

msg = "{FB;01;4C|64:KDY;KMT;KYR;KT0;TKK;PAC;UD01;UD02;UD03;ID01;ID02;ID03;SYS|"
sum = 0;
pChar = msg + 1; // sum starts after the opening {
while (*pChar != 0) {
  sum += (int)*pChar++;
}
sprintf(s, "%04X}", sum);
strcat(msg, s);

Go -> Results in {FB;01;4C|64:KDY;KMT;KYR;KT0;TKK;PAC;UD01;UD02;UD03;ID01;ID02;ID03;SYS|004A}

msg := "{FB;01;4C|64:KDY;KMT;KYR;KT0;TKK;PAC;UD01;UD02;UD03;ID01;ID02;ID03;SYS|"
var sum uint8
for i := 1; i < len(msg); i++ {
    sum += msg[i]
}
s := fmt.Sprintf("%04X}", sum)
req := strings.Join([]string{msg, s}, "")
fmt.Println(req)

Answer 1

In your C code, the type of sum is int, which is a signed integer type at least 16 bits in size¹.

However, the type of sum is uint8 in your Go code, an unsigned integer type limited to 8 bits.

Judging by your format string %04X}, you probably are wanting a 16-bit value.

To fix the Go code, just change uint8 to int and use sum += int(msg[i]) to make the compiler happy. If you want to keep the value of sum strictly 16-bit, you could use uint16 instead and sum += uint16(msg[i]).

If you're wondering why you need to wrap msg[i] in uint16(...), it's because you're converting the value to a different type. C has "integer promotion" rules that automatically convert a value that has a width less than int to a value of type int. Go, however, has no such rules and simply refuses to compile, stating that the types are incompatible.

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By the way, you could simply do this in your Go code due to its automatic memory management:

req := msg + fmt.Sprintf("%04X}", sum)
fmt.Println(req)

or even:

s := fmt.Sprintf("%04X}", sum)
fmt.Println(msg + sum)

Nothing wrong with your current approach; it's just extra verbose.

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¹int is required to be at least 16-bit in C and at least 32-bit in Go, but it is commonly 32-bit these days in both languages. You should be aware, however, that it could be 64-bit on some current systems and could very well be 64-bit by default at some point in the future for either language; they're not required to keep their data type sizes synchronized. You should keep this in mind when adding the values in msg to ensure the value of sum is 16-bit (or just use uint16).