Binary search implementation to search a value of type T1 within a list of T2 type which comparable by value argument.

BinarySearch

using System;
using System.Collections.Generic;

public static class Helper
{
    /// <summary>
    /// Searches a section of the list for a given element using a binary search
    /// algorithm.
    /// </summary>
    /// <param name="items">list of <see cref="TItems"/>, which must be searched within</param>
    /// <param name="index">offset to beginning search</param>
    /// <param name="count">count of elements must be searched after offset</param>
    /// <param name="value">the value of type <see cref="TValue"/> to search</param>
    /// <returns>Found your value index in list</returns>
    public static int BinarySearch<TItems, TValue>(this IList<TItems> items, int index, int count, TValue value) 
            where TItems : IComparable<TValue>
    {
        if (index < 0 || count < 0)
            throw new ArgumentOutOfRangeException((index < 0 ? nameof(index) : nameof(count)));
        if (items.Count - index < count)
            throw new ArgumentException("Argument has invalid len from index for count");

        var lo = index;
        var hi = index + count - 1;
        // ReSharper disable once TooWideLocalVariableScope
        int mid; // declared here for performance
        while (lo <= hi)
        {
            mid = (lo + hi) / 2;
            var r = items[mid].CompareTo(value);
            if (r == 0)
                return mid;
            if (r < 0)
                hi = mid - 1;
            else
                lo = mid + 1;
        }

        // return bitwise complement of the first element greater than value.
        // Since hi is less than lo now, ~lo is the correct item.
        return ~lo;
    }

    /// <summary>
    /// Searches a section of the list for a given element using a binary search
    /// algorithm.
    /// </summary>
    public static int BinarySearch<TItems, TValue>(this IList<TItems> items, TValue value) 
            where TItems : IComparable<TValue>
    {
        return items.BinarySearch(0, items.Count, value);
    }
}