C#，位&字节-如何从字节中检索位值? [英] C#, bits & bytes - How do I retrieve bit values from a byte?

问题描述

我正在从单个字节读取一些值.在用户手册中告诉我，这个字节包含3个不同的值.有一个看起来像这样的表:

I'm reading some values from a single byte. I'm told in the user-manual that this one byte contains 3 different values. There's a table that looks like this:

我解释说，精度占3位，小数位占2位，大小占3位，共8个(1字节).

I interpret that has meaning precision takes up 3 bits, scale takes up 2 and size takes up 3 for a total of 8 (1 byte).

我不清楚的是:

1-为什么将其标记为7到0而不是0到7(可能与重要性有关?)

1 - Why is it labeled 7 through 0 instead of 0 through 7 (something to do with significance maybe?)

2-如何从一个字节中提取单个值?

2 - How do I extract the individual values out of that one byte?

推荐答案

习惯上根据字节的重要性对字节进行编号:位 x 表示 2 ^ x .根据这种编号方式，最低有效位的编号为零，下一位为编号，依此类推.

It is customary to number bits in a byte according to their significance: bit x represents 2^x. According to this numbering scheme, the least significant bit gets number zero, the next bit is number one, and so on.

获取单个位需要进行移位和屏蔽操作:

Getting individual bits requires a shift and a masking operation:

var size = (v >> 0) & 7;
var scale = (v >> 3) & 3;
var precision = (v >> 5) & 7;

在您需要获取的最右边部分的右边移位位数(忽略零移位；我出于说明目的将其添加).

Shift by the number of bits to the right of the rightmost portion that you need to get (shifting by zero is ignored; I added it for illustration purposes).

具有与您要获取的位数相对应的最高编号的遮罩:1表示一位，3表示两位，7表示三位， 2 ^ x-1 x 位.

Mask with the highest number that fits in the number of bits that you would like to get: 1 for one bit, 3 for two bits, 7 for three bits, 2^x-1 for x bits.

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