对于StringBuilder自动分配空间的疑惑

[netreptile]

有很多朋友提出，StringBuilder中Capacity的值是成倍扩充的，但是我今天使用StringBuilder的时候发现了在某些情况下其Capacity不是成倍扩充的，望高手能给出解释，谢谢！下面是具体代码及执行结果
System.Text.StringBuilder sb = new System.Text.StringBuilder();
Console.WriteLine("Capacity:" + sb.Capacity);
Console.WriteLine("Length:" + sb.Length);
sb.Append('1',16);
Console.WriteLine("Capacity:" + sb.Capacity);
Console.WriteLine("Length:" + sb.Length);
sb.Append('2',32);
Console.WriteLine("Capacity:" + sb.Capacity);
Console.WriteLine("Length:" + sb.Length);
sb.Append('3',64);
Console.WriteLine("Capacity:" + sb.Capacity);
Console.WriteLine("Length:" + sb.Length);
try
{
sb.Remove(0,sb.Length);
Console.WriteLine("Capacity:" + sb.Capacity);
Console.WriteLine("Length:" + sb.Length);
sb.Capacity = 1;
sb.Append('a',2);
Console.WriteLine("Capacity:" + sb.Capacity);
Console.WriteLine("Length:" + sb.Length);
sb.Append('b',4);
Console.WriteLine("Capacity:" + sb.Capacity);
Console.WriteLine("Length:" + sb.Length);
sb.Append('c',6);
Console.WriteLine("Capacity:" + sb.Capacity);
Console.WriteLine("Length:" + sb.Length);
}
catch(ArgumentOutOfRangeException e)
{
Console.WriteLine(e.Message);
return;
}
catch(Exception ex)
{
Console.WriteLine(ex.Message);
return;
}
Console.ReadLine();
其执行结果是：
Capacity:16 Length:0
Capacity:16 Length:16
Capacity:49 Length:48
Capacity:113 Length:112
Capacity:113 Length:0
Capacity:3 Length:2
Capacity:7 Length:6
Capacity:14 Length:12

[真相重于对错]

测试代码有问题？？
这是stringbuilder添加元素所进行的操作

private string GetNewString(string currentString, int requiredLength)
{
requiredLength++;
if (requiredLength < 0)
{
throw new OutOfMemoryException();
}
if (requiredLength > this.m_MaxCapacity)
{
throw new ArgumentOutOfRangeException(Environment.GetResourceString("ArgumentOutOfRange_NegativeCapacity"), "requiredLength");
}
int num1 = currentString.Capacity * 2;//注意这里
if (num1 < requiredLength)//还有这里
{
num1 = requiredLength;
}
if (num1 > this.m_MaxCapacity)
{
num1 = this.m_MaxCapacity;
}
if (num1 <= 0)
{
throw new ArgumentOutOfRangeException(Environment.GetResourceString("ArgumentOutOfRange_NegativeCapacity"));
}
return string.GetStringForStringBuilder(currentString, num1);
}

[netreptile]

但是Capacity的大小为什么有113这些呢

[真相重于对错]

你最好用反编译软件看看StringBuilder的实现，上面那些代码就是我用工具反编译的的，
因为代码比较多一些，我不好往上全贴，简单的说就是stringbuilder最后一位需要加一个'\0'来代表字符串结束。
internal unsafe void AppendInPlace(char value, int repeatCount, int currentLength)
{
int num1 = currentLength + repeatCount;
fixed (char* chRef1 = &this.m_firstChar)
{
int num2 = currentLength;
while (num2 < num1)
{
chRef1[num2] = value;
num2++;
}
chRef1[num2] = '\0';//这里

}
this.m_stringLength = num1;
}