Questions about stringtest

[bin]

I used my Jack files to do the tests, and the following problems occurred when testing stringtest.


Later I found out that the problem was math. VM because I used the math. VM provided by the system to do the test, no problem, once I changed to my own math. vm, there are more problems.


The problem should be in -32767 and -32123 because they exceed the 16 digit range.

So display errors.

How should I deal with this problem?




以下是我相关的代码
```
    /** Sets this string to hold a representation of the given value. */
    method void setInt(int n) {
        let len = 0;
        if (n < 0) {
            let n = -n;
            do appendChar(45);
        }

        do setInt2(n);
        return;
    }

    method void setInt2(int n) {
        var int nextN;

        if (n < 10) {
            do appendChar(String.d2c(n));
        } else {
            let nextN = n / 10;
            do setInt2(nextN);
            do appendChar(String.d2c(n - (nextN * 10)));
        }

        return;
    }

     function int multiply(int x, int y) {
        var int sum, index, mask;

        let mask = 1;
        while (index < 16) {
            if (y & mask) {
                let sum = sum + x;
            }
            let x = x + x;
            let index = index + 1;
            let mask = mask + mask;
        }

        return sum;
    }

    function int divide(int x, int y) {
        var int q;

        if (y = 0) {
            do Sys.error(3);
            return 0;
        }

        let q = Math._div(Math.abs(x), Math.abs(y));

        if ((x < 0) = (y < 0)) {
            return q;
        } else {
            return -q;
        }
    }

    function int _div(int x, int y) {
        var int q, result, sum;

        if ((y > x) | ~(y < 16384)) {
            return 0;
        }

        let q = Math.divide(x, y + y);
        let sum = q + q;

        if ((x - (sum * y)) < y) {
            let result = sum;
        } else {
            let result = sum + 1;
        }

        return result;
    }
```

[cadet1620]

Both these are legal 16-bit 2's complement numbers.

-32767 = 1000 0000 0000 0001
-32123 = 8000 0010 1000 0101

The problem is likely in your Math.divide.  The provided algorithm for divide has this line:
    q = divide(x, 2*y)
and the problem is that 2*y can be too big for 16-bit signed ints.

you need to prevent this call if y is too big.

    if (y < 16384) {
        q = Math.divide (x, y+y);  // 2*y is OK to compute
    } else {
        q = 0;  // 2*y is greater than any possible x, q must be 0
    }