JavaScript：读取3个字节Buffer作为整数 | 读取3个字节Buffer作为整数

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问题描述

假设我有一个十六进制数据流，我想把它分成3个字节的块，我需要读取整数。

Let's say I have a hex data stream, which I want to divide into 3-bytes blocks which I need to read as an integer.

例如：给定十六进制字符串 01be638119704d4b9a 我需要读取前三个字节 01be63 并将其读作整数 114275 。这就是我得到的：

For example: given a hex string 01be638119704d4b9a I need to read the first three bytes 01be63 and read it as integer 114275. This is what I got:

var sample = '01be638119704d4b9a';
var buffer = new Buffer(sample, 'hex');
var bufferChunk = buffer.slice(0, 3);
var decimal = bufferChunk.readUInt32BE(0);

readUInt32BE 适用于4字节数据，但在这里我显然得到：

The readUInt32BE works perfectly for 4-bytes data, but here I obviously get:

RangeError: index out of range
  at checkOffset (buffer.js:494:11)
  at Buffer.readUInt32BE (buffer.js:568:5)

如何我是否正确读取3字节作为整数？

How do I read 3-bytes as integer correctly?

推荐答案

如果您使用的是node.js v0.12 +或io.js ，有允许可变数量的字节：

If you are using node.js v0.12+ or io.js, there is buffer.readUIntBE() which allows a variable number of bytes:

var decimal = buffer.readUIntBE(0, 3);

（请注意，Big Endian的 readUIntBE 对于Little Endian， readUIntLE 。

(Note that it's readUIntBE for Big Endian and readUIntLE for Little Endian).

否则，如果您使用的是较旧版本的节点，则会有手动完成（当然首先检查边界）：

Otherwise if you're on an older version of node, you will have to do it manually (check bounds first of course):

var decimal = (buffer[0] << 16) + (buffer[1] << 8) + buffer[2];

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