介绍TransferSizes的实现。
1. 基本定义
从min到max的闭合区间：[min, max]
判断条件：
a. min和max为2的幂；
b. min <= max;
c. min和max为非负整数；
d. min和max必须同时为0；
2. none
因为min和max必须同时为0，所以只需要判断min是否为0即可：
3. contains
判断this是否包含x，即x落在this的范围内：
4. containsLg
判断this是否包含2^x。
5. intersect
计算this和x的交集。
6. 伴生对象
a. 构造方法：min = max = x;
b. none对象：min = max = 0;
c. asBool：x是否为空；
7. 附录
TransferSizes：
// An potentially empty inclusive range of 2-powers [min, max] (in bytes)
case class TransferSizes(min: Int, max: Int)
{
def this(x: Int) = this(x, x)
require (min <= max, s"Min transfer $min > max transfer $max")
require (min >= 0 && max >= 0, s"TransferSizes must be positive, got: ($min, $max)")
require (max == 0 || isPow2(max), s"TransferSizes must be a power of 2, got: $max")
require (min == 0 || isPow2(min), s"TransferSizes must be a power of 2, got: $min")
require (max == 0 || min != 0, s"TransferSize 0 is forbidden unless (0,0), got: ($min, $max)")
def none = min == 0
def contains(x: Int) = isPow2(x) && min <= x && x <= max
def containsLg(x: Int) = contains(1 << x)
def containsLg(x: UInt) =
if (none) Bool(false)
else if (min == max) { UInt(log2Ceil(min)) === x }
else { UInt(log2Ceil(min)) <= x && x <= UInt(log2Ceil(max)) }
def contains(x: TransferSizes) = x.none || (min <= x.min && x.max <= max)
def intersect(x: TransferSizes) =
if (x.max < min || max < x.min) TransferSizes.none
else TransferSizes(scala.math.max(min, x.min), scala.math.min(max, x.max))
override def toString() = "TransferSizes[%d, %d]".format(min, max)
}
object TransferSizes {
def apply(x: Int) = new TransferSizes(x)
val none = new TransferSizes(0)
implicit def asBool(x: TransferSizes) = !x.none
}