如何从在C中提取一些特定位？ [英] How to extract specific bits from a number in C?

问题描述

我需要提取特定部分（无位）一个短 C语言的数据类型。

I need to extract specific part (no of bits) of a short data type in C.

例如我有52504二进制为11001101000 11000，我想首先6（FROM LSB - > MSB即十进制011000 24）位和10位（11001101000十进制820）

For Example I have a binary of 52504 as 11001101000 11000 and I want First 6 ( FROM LSB --> MSB i.e 011000 decimal 24) bits and rest of 10 bits ( 11001101000 decimal 820).

同样我想这个功能太推广到提取特定没有给出开始和位结束（位即相当于大块一些十进制值）。

Similarly I want this function to be too generalized to extract specific no of bits given "start" and "end" (i.e chunks of bits equivalent with some decimal value).

我检查的其他职位，但这些都没有帮助，给出功能都没有太大一概而论。

I checked other posts, but those were not helpful, as given functions are not too much generalized.

我需要的东西，可以适用于C 短数据类型。

I need something that can work for short data type of C.

我有大小2048字节的短阵。其中，每个像素是10比特。所以，我的16位由每个字节占用一些时间2个像素数据，有时3个像素的数据。

I am having the short array of size 2048 bytes. Where each Pixel is of 10 bits. So my 16 bit consisting each byte occupying some time 2 pixels data, sometimes 3 pixels data.

如同

（PIXEL：0,1）
 10位+ 6位

( PIXEL : 0,1 ) 10 BITS + 6 BITS

然后（PIXEL：1,2,3）
 4位（第1像素其余位）+ 10位+ 2位。

then ( PIXEL : 1,2,3 ) 4 BITS ( 1st pixels remaining bits ) + 10 BITS + 2 BITS.

等..this模式继续下去...
因此，所有我想提取每个像素，并让每个像素的整个阵列wholy在被占用对全字节（16位）喜欢..
1字节应含有1数据的像素，其他字节应包含在整个16位其他象素值等等等等。

and so on ..this pattern continues ... So, all I want to extract each pixel and make an entire array of having each pixels to be occupied wholy in on WHOLE BYTE ( of 16 bits ) like.. 1 byte should contain 1 DATA PIXEL, the other BYTE should contain other PIXEL value in whole 16 bits and so on so forth.

推荐答案

有你需要知道两积木搭建这个自己：

There are two building blocks that you need to know to build this yourself:

• 获得 N 至少显著位需要构建的位掩码的有 N 那些在结束。你不喜欢这样：（（1 <<;＆LT; N）-1）。 1 LT;＆LT; ñ是 2 ^ N ：它有一个 1 在 N + 1 ST位置，之后全部为零。减人给你，你需要的掩码。


• 丢弃 M 至少显著位是一个简单的右移： K＆GT;＆GT;中号

• Getting N least significant bits requires constructing a bit mask with N ones at the end. You do it like this: ((1 << N)-1). 1 << N is 2 ^ N: it has a single 1 at the N+1st position, and all zeros after it. Subtracting one gives you the mask that you need.
• Dropping M least significant bits is a simple shift to the right: k >> M

现在您从 M 切割出 N 算法变成了两个步骤：你转移原值 M 位到右侧，然后执行逐位和与面具 NM 的。

Now your algorithm for cutting out from M to N becomes a two-step process: you shift the original value M bits to the right, and then perform a bit-wise AND with the mask of N-M ones.

#define LAST(k,n) ((k) & ((1<<(n))-1))
#define MID(k,m,n) LAST((k)>>(m),((n)-(m)))

int main() {
    int a = 0xdeadbeef;
    printf("%x\n",  MID(a,4,16));
    return 0;
}

该片段从4，包括削减了位，16个，独家，并打印蜂当你运行它。位从零开始编号。

This fragment cuts out bits from 4, inclusive, to 16, exclusive, and prints bee when you run it. Bits are numbered from zero.

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