ArrayList IListWrapper integer overflow in BinarySearch

[vcsjones]

Consider the following program:

using System;
using System.Collections;

static class Foo
{    
    static void Main()
    {
        IList l = new byte[int.MaxValue / 2 + 2];
        ArrayList al = ArrayList.Adapter(l);
        int result = al.BinarySearch((byte)1);
        Console.WriteLine(result);
    }
}

This will overflow here:

runtime/src/libraries/System.Private.CoreLib/src/System/Collections/ArrayList.cs

Line 774 in be04169

mid = (lo + hi) / 2;

I would instead expect this to return a value indicating it could not be found.

The GetMedian method on Array is likely the "right" implementation to use for calculating mid.

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