bitvec 0.2.3

Fast & Simple bit manipulation library implemented in rust

BitVec

Tools written for python for fast and simple bit manipulation It is:

• Simpler to manipulate bits than with native python ints
• Able to correctly wrap numbers in arithmetic operations
• Emulate behavior of unsigned, signed integers
• Unit-tested
• Written in Rust (Some operations are quite fast)

Installation

pip install bitvec

Unittests

python -m unittest python\tests\tests.py

PyPi

https://pypi.org/project/bitvec/

Example use:

from bitvec import Binary
from bitvec import arithm

# Creating new number. Size is inferred from leading zeros
x = Binary('0110')
y = Binary(1, lenght=9) # You can specify len too

print(f"{x}, lenght: {len(x)}") # prints '0110, lenght: 4'

print(int(~(x+y))) # prints 504 (0b111111000)

# Arithmetic correctly wraps and you can check the status
# overflowing_add return the wrapped sum and boolen to indicate if overflow occurs
print(arithm.overflowing_add(x, '1100')) # (0010, True)

# Set first bit to high
x[0] = True 

# slice bits
print(x[:3]) # ('111')

# sets first 3 bits to '001'
x[:3] = "001" 

# convert to hex
print(x.hex()) # '0x1'

# every second bit of '0001' 
print(x[::2]) # '01'    ^ ^

# you can quickly iterate over bits, bytes or any other chunk of bits with .iter(size) function
for i in x.iter(2):
    print("Chunk of two bits: ", i) # i is `01` then `00`

# count all zeros
print(x.count_zeros())  # prints 3

# find indexes of all zeros
print(x.find_all('0')) # prints [1, 2, 3] 

Brief docs

Binary

Class that represent numbers in binary. Wraps arithmetic to bouds of the binary number, allows for quick and easy bit manipulation.

Parameters

• object - Any object that can be somehow converted to binary number. Including its representation as string, int, boolean, list of boolean-convertable values, byte-arrays, numpy arrays ect.
• lenght - Target lenght of the number in bits. This number can be inferred from object based on its value, extra zeros ect
• bytes_lenght - Target lenght of the number in bytes. Same as lenght but in bytes.
• sign_behavior - How number should implement sign.

Examples

>>> from bitvec import Binary
>>> Binary("0110") # From string representing binary number. Following zeros are used to inherit len of number.
'0110'
>>> Binary(4, lenght=8) # Crate number with 8 bits, 4 is converted to binary and padded with zeros.
'00000100'
>>> Binary(255)
'11111111'
>>> Binary([True, 0, 1, 1.0]) # From array of boolean-likes
'1011'
>>> Binary("0000 0001") # Ignores whitespace
'00000001'
>>> Binary("ff Aa C   C") # Works with hex too
'11111111 10101010 11001100'

Alias

Module defines factories with predefined sizes and behaviors like u8, u16, i16, i64 ect. These ones can be used as followed:

>>> from bitvec.alias import u8
>>> u8(3)
'00000011'

Conversion

>>> num = Binary("FA") # 11111010

To string (formatted binary)

>>> str(num) # Returns just bits
'11111010'
>>> bin(num)
'0b11111010'
>>> num.bin()
'0b11111010'
>>> num.bin(prefix=False) # remove prefix 
'11111010'
>>> hex(num)
'0xfa'
>>> num.hex()
'0xfa'
>>> num.hex(prefx=False)
'fa'

>>> int(num)
250
>>> num.int()
250

To boolean (False when 0)

>>> bool(num)
True

Indexing and Access

Index

Bits of the number can be accessed throught index:

>>> num = Binary("FA") # 11111010
>>> num[0], num[1], num[2] # First 3 bits of the number
(False, True, False)
>>> num[-1] # Last bit
True

Slice

>>> num[:3] # from start to 3th bit (first 3 bits)
'010'
>>> num[-6:] # from 6th bit from the end to end (last 6 bits)
'111110'
>>> num[-6:-2] # From 6th bit from end to 2st bit from end
'1110'
>>> num[2:] # Skip first 2 bits
'111110'
>>> num[:16] # First 16 bits (padded with zeros)
'00000000 11111010'
>>> num[::2] # Every other bit
'1100'
>>> num[::-1] # Reversed
'01011111'
>>> num[[1,3]] # Get second and 4th bit
'11'

NOTE that behavior of slicing is slighty diffrent from slicing pythons str or list, first bit is from far right, not left. You can also exeed len of the value, in this case added bits will be padded with sign extending bit (0 for unsigned, sign_bit for singed)

Note that slicing makes a copy of the vector

Public Methods

Aliases for slicing number

• high_byte() - second 8bits (from 8th to 16th)
• low_byte() - first 8bits (from start to 8th)
• extended_low() - first 16bits
• extended_high() - second 16bits
• get_byte(index: int) - nth group of 8-bit chunks.

Information about number

• sign_behavior() - The way that number behaves on extending and converstions signed or unsigned
• maximal_value() - Maximal possibe value than can be hold in this representation and lenght
• minimal_value() - Minimal possibe value than can be hold in this representation and lenght
• is_negative() - Returns if number is negative
• sign_extending_bit() - Returns the boolean that will be used to extend this value to left
• hex(prefix: bool=True) - hex representation of this number
• bin(prefix: bool=True)- bin representation of this number
• int() - casted to python integer

Searching & Finding Patterns

• leading_zeros() - Amount of leading zeros in the number
• trailing_zeros() - Amount of trailing zeros in the number
• leading_ones() - Amount of leading ones in the number
• trailing_ones() - Amount of trailing ones in the number
• find(sub: bool|int|str|Binary) - Find first occurence (index) of the pattern
• find_all(sub: bool|int|str|Binary) - Find all occurences (index) of the pattern
• find_zeros() - Find indexes of zeros
• find_ones() - Find indexes of ones
• count_zeros() - count how many zeros is in number
• count_ones() - count how many ones is in number

Modifying

• append(Binary|bool|str|int) - Appends value to the end
• prepend(Binary|bool|str|int) - Appends vakue to the start

Iterating

• bits() - iterates over bits
• bytes() - iterates over bytes
• iter() - iterates over chunks or n bits

Modify by Index

You can modify bits with indexes:

>>> num = Binary(0, lenght=8)
>>> num[0] = True # Set first bit to high
>>> num[1] = True # Set second bit to high
>>> num
'00000011'
>>> num[-1] = True # Set last bit to high
>>> num
'10000011'
>>> num[0] = 0 # Set first bit to low
>>> num
'10000010'

Modify by Slice

You can select bits by slice and set them, or copy from other number

>>> num = Binary(0, lenght=8)
>>> num[:3] = True
>>> num
'00000111'
>>> num[:3] = "101" # Insert 101 in place of first 3 bits of the number
>>> num
'00000101'
>>> num[5:8] = "111" # insert 111 in place of bits 5th 6th 7th
>>> num
'11100101'
>>> num[:] = 0 # Set all bits to 0
>>> num
'00000000'

Modify by indeces

>>> num = Binary(0, lenght=8)
>>> num[[1,2,3]] = True # Set first, second and third bit to True
>>> num
>>> '0000 1110'

There is few rules

• If right side of the slice is convertable to Binary, it will be converted to binary and inserted in place of the selected bits.
• If size of the converted value will be greater than size of the selected bits, it will throw an error.
• If right side is boolean the assigment will set all selectet bits to this value.
• step value is not supported.

Iterating over bits or chunks

You can iterate over bits of the number:

>>> num = Binary("FA") # 11111010
>>> for bit in num: # or num.bits()
...     print(bit, end=" ")  # bit is Binary class with lenght equal to 1 
0 1 0 1 1 1 1 1

Or over bytes:

>>> num = Binary("FA") # 11111010
>>> list(num.extended_low().bytes())
[11111010, 00000000] 

Or over any other chunk of bits with iter function. For more sophisticated iteration you can use itertools or just play with indexing and slicing.

Arithmetic

In module arithm there are functions that can be used to perform arithmetic/logical operations on binary numbers. That's includes

• Addition - wrapping_add and others
• Subtraction - wrapping_sub and others
• Multiplication - wrapping_mul and others
• Shifts - overflowing_lsh, wrapping_rsh and others
• Bitwise operations - bitwise_and, bitwise_or and others
• Casting & Conversions - cast, pad_zeros and others

Import this submodule and check all of them!

>>> from bitvec import arithm
>>> arithm.wrapping_add(u4("1111"), "0001") 
'0000' # 15 + 1 = 16, but we have only 4 bits, so we wrap around and get 0
>>> arithm.overflowing_add(u4("1111"), "0001")
('0000', True) # If you want to know if there was overflow, use overflowing_add
>>> arithm.overflowing_lsh(u8('0100 1010'), 2)
('00101000', '01') # 0100 1010 << 2 = 0010 1000, but we have only 8 bits, so we wrap around to get 0010 1000, and we have 2 'wrapped' bits from left, so we return them as second value

Some functions are implemented for Binary class (usually wrapping ones), so you can use them directly with operators number:

>>> u8("0100 1010") + u8("0000 0010")
'0100 1100'

That includes:

• __add__, __sub__, __mul__, __lshift__, __rshift__, __and__, __or__, __xor__, __invert__, __neg__

Creating numbers - details

• If you didn't specify lenght, it will be calculated from value
  • For string it will be lenght of string including leading zeros/ones
  • For int it will be minimal lenght of binary representation of the number
• If you specify lenght, it will be used but if value is longer, it will raise an error

This module assumes that for signed numbers the most significant bit is sign bit. So for signed number with lenght of 1 (so we have only sign_bit that has weight equal to -1) possible values will be 0 and -1 Numbers with lenght of 0 will be always treated as 0

Examples

>>> Binary(0                        )  # lenght will be 0, displayed as ''
>>> Binary(0,               lenght=1)  # lenght will be 1, displayed as '0'
>>> Binary(0,               lenght=2)  # lenght will be 2, displayed as '00'
>>> Binary(0,  signed=True          )  # lenght will be 0, displayed as '0'
>>> Binary(0,  signed=True, lenght=1)  # lenght will be 1, displayed as '0'
>>> Binary(-1, signed=True, lenght=1)  # lenght will be 1, displayed as '1'
>>> Binary(-1, signed=True, lenght=2)  # lenght will be 2, displayed as '11'
>>> Binary(1,  signed=True          )  # lenght will be 2, displayed as '01'

This behavior is based on the interpretation of the number as a signed integer where sign bit is treated as it has negative weight

for unsigned:

0 0 0 0
 \ \ \ \_ weight 1
  \ \ \__ weight 2
   \ \___ weight 4
    \____ weight 8
Value = sum of weights of bits set to 1

for signed:
    
0 0 0 0
 \ \ \ \_ weight  1
  \ \ \__ weight  2
   \ \___ weight  4
    \____ weight -8
Value = sum of weights of bits set to 1

for size 1
unsigned:
0
 \_ weight 1
signed:
0
 \_ weight -1 (last bit)

And zero-lenght number just fills up the pattern well.