将 4 个整数打包为一个字节? [英] Packing 4 Integers as ONE BYTE?

问题描述

我有四个整数 {a, b, c, d} 可以有以下范围值:

I have four integers {a, b, c, d} that can have the following range of values:

a - {0 或 1}(1 位)

a - {0 or 1} (1 bit)

b - {0 或 1}(1 位)

b - {0 or 1} (1 bit)

c - {0, 1, 2, ..., 7}(3 位)

c - {0, 1, 2, ..., 7} (3 bits)

d - {0, 1, 2, ..., 7}(3 位)

d - {0, 1, 2, ..., 7} (3 bits)

首先，我想将它们打包成一个字节，然后可以写入二进制文件.稍后，我想解压该字节并将其转换为形式 (a, b, c, >d).

at first, I would like to pack them into a one byte that can be then written to a binary file. later, I would like to unpack that one byte and get from it to a tuple of the form (a, b, c, d).

我知道如何在 python 中读/写一个字节到二进制文件.但是我如何进行位打包/解包?

I know how to read/write a byte to a binary file in python. But how do I do the bits packing/unpacking?

推荐答案

使用移位和按位或，然后转换为字符得到一个字节":

Use shift and bitwise OR, then convert to a character to get a "byte":

x = chr(a | (b << 1) | (c << 2) | (d << 5))

要再次解包这个字节，首先转换为整数，然后移位并使用按位与:

To unpack this byte again, first convert to an integer, then shift and use bitwise AND:

i = ord(x)
a = i & 1
b = (i >> 1) & 1
c = (i >> 2) & 7
d = (i >> 5) & 7

解释:最初，你有

0000000a
0000000b
00000ccc
00000ddd

左移给你

0000000a
000000b0
000ccc00
ddd00000

按位 OR 结果

dddcccba

转换为字符会将其转换为单个字节.

Converting to a character will convert this to a single byte.

拆包:四种不同的右移结果

Unpacking: The four different right-shifts result in

dddcccba
0dddcccb
00dddccc
00000ddd

使用 1 (0b00000001) 或 7 (0b00000111) 屏蔽(按位与)结果>

Masking (bitwise AND) with 1 (0b00000001) or 7 (0b00000111) results in

0000000a
0000000b
00000ccc
00000ddd

再来一次.

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