为什么UTF-32存在，只需要21位来编码每个字符？ [英] Why UTF-32 exists whereas only 21 bits are necessary to encode every character?

问题描述

我们知道代码点可以在这个小于2 ^ 21的区间0..10FFFF。那么为什么我们需要UTF-32，当所有的代码点可以用3个字节表示？ UTF-24应该足够了。

解决方案

我可以想到的两个原因：

• 它允许将来扩展


• （更重要的是）计算机在处理4字节边界上的数据时通常会更好。与在3字节边界上工作的痛苦相比，减少内存消耗的好处相对较小。

我猜这是有点像为什么我们经常有8位，16位，32位和64位整数数据类型（byte，int，long，whatever）而不是24位的。我确定有很多场合，我们知道一个数字永远不会超过2 ²¹ ，但使用 int 更简单创建一个24位类型。

We know that codepoints can be in this interval 0..10FFFF which is less than 2^21. Then why do we need UTF-32 when all codepoints can be represented by 3 bytes? UTF-24 should be enough.

解决方案

Two reasons I can think of:

• It allows for future expansion
• (More importantly) Computers are generally much better at dealing with data on 4 byte boundaries. The benefits in terms of reduced memory consumption are relatively small compared with the pain of working on 3-byte boundaries.

I guess this is a bit like asking why we often have 8-bit, 16-bit, 32-bit and 64-bit integer datatypes (byte, int, long, whatever) but not 24-bit ones. I'm sure there are lots of occasions where we know that a number will never go beyond 2²¹, but it's just simpler to use int than to create a 24-bit type.

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