[Java] RSync Rolling Checksum

Hallo zusammen,

ich versuche die fortlaufende Prüfsumme in rsync nachzubauen.
https://rsync.samba.org/tech_report/node3.html

Es geht mir nicht um Geschwindigkeit, sondern um Verständnis.
Mein Code:

Code:

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    public static int[] calcPruef(int k,int l, int x[], int M) {
        int result_a = 0, result_b = 0, result_s = 0;
       
        for(int i = k; i <= l; i++) { result_a += x[i-1]; }
        result_a = result_a % M;
       
        for(int i = k; i <= l; i++) { result_b = (l-i+1)*x[i-1]; }
        result_b = result_b % M;
       
        result_s = result_a + M*result_b;
        return new int[] {result_a,result_b,result_s};
    }
   
    public static int[] calcPruefNext(int k,int l, int x[], int M,int result_a, int result_b) {
        int result_a_new = 0, result_b_new = 0, result_s = 0;
        result_a_new = (result_a-x[k-1]+x[l-1+1]) % M;   
        result_b_new = (result_b - (l-k+1)*x[k-1] + result_a_new) % M;
        result_s = result_a_new + M*result_b_new;
        return new int[] {result_a_new,result_b_new,result_s};
    }

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Die Berechnung der Funktion calcPruef scheint zu passen:

Code:

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x = new int[] {9,8,7,6,5};
        k = 1;
        l = 5;
        result = calcPruef(k,l,x,M);
        System.out.println("Result " + Arrays.stream(Arrays.copyOfRange(x,k-1,l-1)).mapToObj(String::valueOf).collect(Collectors.joining(",")) + " = " + result[0] + " | " + result[1] + " | " + result[2]);
       
        x = new int[]{4,2,5,9,8,7,6,5};
        k = 4;
        l = 8;
        result = calcPruef(k,l,x,M);
        System.out.println("Result " + Arrays.stream(Arrays.copyOfRange(x,k-1,l-1)).mapToObj(String::valueOf).collect(Collectors.joining(",")) + " = " + result[0] + " | " + result[1] + " | " + result[2]);

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Ergebnis:

Code:

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Result 9,8,7,6 = 3 | 5 | 163
Result 9,8,7,6 = 3 | 5 | 163

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Jetzt mein Problem. Wenn ich folgende Ausführe:

Code:

---

x = new int[] {9,8,7,6,5};
        k = 1;
        l = 5;
        result = calcPruef(k,l,x,M);
        System.out.println("Result " + Arrays.stream(Arrays.copyOfRange(x,k-1,l-1)).mapToObj(String::valueOf).collect(Collectors.joining(",")) + " = " + result[0] + " | " + result[1] + " | " + result[2]);
       
        x = new int[]{3,9,8,7,6,5};
        k = 1;
        l = 5;
        result = calcPruef(k,l,x,M);
        System.out.println("Result " + Arrays.stream(Arrays.copyOfRange(x,k-1,l-1)).mapToObj(String::valueOf).collect(Collectors.joining(",")) + " = " + result[0] + " | " + result[1] + " | " + result[2]);
           
        //Über Fortlaufende Prüfsumme
        result = calcPruefNext(k,l,x,M,result[0],result[1]);
        l += 1;
        k += 1;
        System.out.println("Result " + Arrays.stream(Arrays.copyOfRange(x,k-1,l-1)).mapToObj(String::valueOf).collect(Collectors.joining(",")) + " = " + result[0] + " | " + result[1] + " | " + result[2]);

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Hätte ich erwartet, dass die das Ergebnis von "calcPruefNext" die Prüfsumme 163 ergibt (und a=3 , b=5)
Ich erhalte jedoch

Code:

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Result 9,8,7,6 = 3 | -6 | -189

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Leider finde ich den Fehler nicht. Die Berechnung von "result_a_new" scheint zu passen (ergibt 3). Aber das "result_b_new" ist -6, erwartet hätte ich aber eine 5.

Kann mir jemand helfen?

Fehler war hier:

Code:

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for(int i = k; i <= l; i++) { result_b += (l-i+1)*x[i-1]; }

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Das "+" hat gefehlt.