Menu
In python, I have been given a 64 bit integer. This Integer was created by taking several different 8 bit integers and mashing them together into one giant 64 bit integer. It is my job to separate them again.
For example:
Source number: 2592701575664680400
Binary (64 bits): 0010001111111011001000000101100010101010000101101011111000000000
int 1: 00100011 (35)
int 2: 11111011 (251)
int 3: 00100000 (32)
int 4: 01011000 (88)
int 5: 10101010 (170)
int 6: 00010110 (22)
int 7: 10111110 (190)
int 8: 00000000 (0)
So what I would like to do is take my source number 2592701575664680373 and return an array of length 8, where each int in the array are the ints listed above.
I was going to use struct, but to be perfectly honest, reading the documentation hasn't made it quite clear exactly how I would accomplish that.
620
An int value can be converted into bytes by using the method int. to_bytes().
32-bits ~ [-231, 231 – 1] = [- 2,147,483,648 , 2,147,483,647 ] 64-bits ~ [-263, 263 – 1] = [ -9,223,372,036,854,775,808 , 9,223,372,036,854,775,807 ]
To convert, or cast, a string to an integer in Python, you use the int() built-in function. The function takes in as a parameter the initial string you want to convert, and returns the integer equivalent of the value you passed. The general syntax looks something like this: int("str") .
We can use the built-in Bytes class in Python to convert a string to bytes: simply pass the string as the first input of the constructor of the Bytes class and then pass the encoding as the second argument. Printing the object shows a user-friendly textual representation, but the data contained in it is in bytes.
In Python 2.x, struct.pack returns a string of bytes. It's easy to convert that to an array of integers.
>>> bytestr = struct.pack('>Q', 2592701575664680400)
>>> bytestr
'#\xfb X\xaa\x16\xbd\xd0'
>>> [ord(b) for b in bytestr]
[35, 251, 32, 88, 170, 22, 189, 208]
The struct module in python is used for converting from python object to byte strings, typically packed according to C structure packing rules. struct.pack takes a format specifier (a string which describes how the bytes of the structure should be laid out), and some python data, and packs it into a byte string. struct.unpack does the inverse, taking a format specifier and a byte string and returning a tuple of unpacked data once again in the format of python objects.
The format specifier being used has two parts. The lead character specifies the endianness (byte order) of the string. The following characters specify the types of the fields of the struct being packed or unpacked. So '>Q' means to pack the given data as a big-endian unsigned long long. To get the bytes in the opposite order, you could use < instead for little-endian.
The final operation is a list comprehension which iterates over the characters of the byte string and uses the ord builtin function to get the integer representation of that character.
Final note: Python doesn't actually have a concept of integer size. In 2.x, there is int which is limited to 32 bits, and long which is of unlimited size. In 3.x those two were unified into a single type. So even though this operation guarantees to give integers that take up only one byte, noting about python will force the resulting integers to stay that way if you use them in other operations.
121
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With
