StringBuilder Extensions

Here are the extensions for StringBuilder that I created to make it work like a string. I have them for years now and finally put in some time to post them here.
 
Phi Nguyen
 

public static string Substring(this StringBuilder sb, int startIndex, int length)
{
    return sb.ToString(startIndex, length);
}
 
public static StringBuilder Remove(this StringBuilder sb, char ch)
{
    for (int i = 0; i < sb.Length; )
    {
        if (sb[i] == ch)
            sb.Remove(i, 1);
        else
            i++;
    }
    return sb;
}
 
public static StringBuilder RemoveFromEnd(this StringBuilder sb, int num)
{
    return sb.Remove(sb.Length - num, num);
}
 
public static void Clear(this StringBuilder sb)
{
    sb.Length = 0;
}
 
/// <summary>
/// Trim left spaces of string
/// </summary>
/// <param name="sb"></param>
/// <returns></returns>
public static StringBuilder LTrim(this StringBuilder sb)
{
    if (sb.Length != 0)
    {
        int length = 0;
        int num2 = sb.Length;
        while ((sb[length] == ' ') && (length < num2))
        {
            length++;
        }
        if (length > 0)
        {
            sb.Remove(0, length);
        }
    }
    return sb;
}
 
/// <summary>
/// Trim right spaces of string
/// </summary>
/// <param name="sb"></param>
/// <returns></returns>
public static StringBuilder RTrim(this StringBuilder sb)
{
    if (sb.Length != 0)
    {
        int length = sb.Length;
        int num2 = length - 1;
        while ((sb[num2] == ' ') && (num2 > -1))
        {
            num2--;
        }
        if (num2 < (length - 1))
        {
            sb.Remove(num2 + 1, (length - num2) - 1);
        }
    }
    return sb;
}
 
/// <summary>
/// Trim spaces around string
/// </summary>
/// <param name="sb"></param>
/// <returns></returns>
public static StringBuilder Trim(this StringBuilder sb)
{
    if (sb.Length != 0)
    {
        int length = 0;
        int num2 = sb.Length;
        while ((sb[length] == ' ') && (length < num2))
        {
            length++;
        }
        if (length > 0)
        {
            sb.Remove(0, length);
            num2 = sb.Length;
        }
        length = num2 - 1;
        while ((sb[length] == ' ') && (length > -1))
        {
            length--;
        }
        if (length < (num2 - 1))
        {
            sb.Remove(length + 1, (num2 - length) - 1);
        }
    }
    return sb;
}
 
/// <summary>
/// Get index of a char
/// </summary>
/// <param name="sb"></param>
/// <param name="c"></param>
/// <returns></returns>
public static int IndexOf(this StringBuilder sb, char value)
{
    return IndexOf(sb, value, 0);
}
 
/// <summary>
/// Get index of a char starting from a given index
/// </summary>
/// <param name="sb"></param>
/// <param name="c"></param>
/// <param name="startIndex"></param>
/// <returns></returns>
public static int IndexOf(this StringBuilder sb, char value, int startIndex)
{
    for (int i = startIndex; i < sb.Length; i++)
    {
        if (sb[i] == value)
        {
            return i;
        }
    }
    return -1;
}
 
/// <summary>
/// Get index of a string
/// </summary>
/// <param name="sb"></param>
/// <param name="text"></param>
/// <returns></returns>
public static int IndexOf(this StringBuilder sb, string value)
{
    return IndexOf(sb, value, 0, false);
}
 
/// <summary>
/// Get index of a string from a given index
/// </summary>
/// <param name="sb"></param>
/// <param name="text"></param>
/// <param name="startIndex"></param>
/// <returns></returns>
public static int IndexOf(this StringBuilder sb, string value, int startIndex)
{
    return IndexOf(sb, value, startIndex, false);
}
 
/// <summary>
/// Get index of a string with case option
/// </summary>
/// <param name="sb"></param>
/// <param name="text"></param>
/// <param name="ignoreCase"></param>
/// <returns></returns>
public static int IndexOf(this StringBuilder sb, string value, bool ignoreCase)
{
    return IndexOf(sb, value, 0, ignoreCase);
}
 
/// <summary>
/// Get index of a string from a given index with case option
/// </summary>
/// <param name="sb"></param>
/// <param name="text"></param>
/// <param name="startIndex"></param>
/// <param name="ignoreCase"></param>
/// <returns></returns>
public static int IndexOf(this StringBuilder sb, string value, int startIndex, bool ignoreCase)
{
    int num3;
    int length = value.Length;
    int num2 = (sb.Length - length) + 1;
    if (ignoreCase == false)
    {
        for (int i = startIndex; i < num2; i++)
        {
            if (sb[i] == value[0])
            {
                num3 = 1;
                while ((num3 < length) && (sb[i + num3] == value[num3]))
                {
                    num3++;
                }
                if (num3 == length)
                {
                    return i;
                }
            }
        }
    }
    else
    {
        for (int j = startIndex; j < num2; j++)
        {
            if (char.ToLower(sb[j]) == char.ToLower(value[0]))
            {
                num3 = 1;
                while ((num3 < length) && (char.ToLower(sb[j + num3]) == char.ToLower(value[num3])))
                {
                    num3++;
                }
                if (num3 == length)
                {
                    return j;
                }
            }
        }
    }
    return -1;
}
 
/// <summary>
/// Determine whether a string starts with a given text
/// </summary>
/// <param name="sb"></param>
/// <param name="value"></param>
/// <returns></returns>
public static bool StartsWith(this StringBuilder sb, string value)
{
    return StartsWith(sb, value, 0, false);
}
 
/// <summary>
/// Determine whether a string starts with a given text (with case option)
/// </summary>
/// <param name="sb"></param>
/// <param name="value"></param>
/// <param name="ignoreCase"></param>
/// <returns></returns>
public static bool StartsWith(this StringBuilder sb, string value, bool ignoreCase)
{
    return StartsWith(sb, value, 0, ignoreCase);
}
 
/// <summary>
/// Determine whether a string is begin with a given text
/// </summary>
/// <param name="sb"></param>
/// <param name="value"></param>
/// <param name="startIndex"></param>
/// <param name="ignoreCase"></param>
/// <returns></returns>
public static bool StartsWith(this StringBuilder sb, string value, int startIndex, bool ignoreCase)
{
    int length = value.Length;
    int num2 = startIndex + length;
    if (ignoreCase == false)
    {
        for (int i = startIndex; i < num2; i++)
        {
            if (sb[i] != value[i - startIndex])
            {
                return false;
            }
        }
    }
    else
    {
        for (int j = startIndex; j < num2; j++)
        {
            if (char.ToLower(sb[j]) != char.ToLower(value[j - startIndex]))
            {
                return false;
            }
        }
    }
    return true;
}