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bit_manipulation/multibit_manipulation.py
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@ -1,7 +1,7 @@
"""Bit integer manipulation, both single bit and multi-bit list-like """Bit integer manipulation, both single bit and multi-bit list-like
slicing functions ( get, set, insert, remove ) implemented with slicing functions ( get, set, insert, remove ) implemented with
builtin bitwise operations. builtin bitwise operations.
See: See:
https://high-python-ext-3-algorithms.readthedocs.io/ko/latest/chapter5.html#insert-bit https://high-python-ext-3-algorithms.readthedocs.io/ko/latest/chapter5.html#insert-bit
https://en.wikipedia.org/wiki/Bit_manipulation#Bit_manipulation_operations https://en.wikipedia.org/wiki/Bit_manipulation#Bit_manipulation_operations
@ -11,22 +11,22 @@ All parameters must be must be int >= 0, referred to as a 'bit integer'.
bint:int bint:int
The bit integer to be accessed or returned as modified. The bit integer to be accessed or returned as modified.
index:int index:int
The offset into the bit position from right, The offset into the bit position from right,
0b010111 -> list [1,1,1,0,1,0]. big-endian -> little-endian 0b010111 -> list [1,1,1,0,1,0]. big-endian -> little-endian
For inserts, index is the position to the right of index, For inserts, index is the position to the right of index,
index 0 -> right of rightmost bit. index 0 -> right of rightmost bit.
For gets, sets and removes, it is the position of the bit itself. For gets, sets and removes, it is the position of the bit itself.
value:int value:int
Either [0,1] for single bit, or bit mask, bit_length(value) <= bitlen. Either [0,1] for single bit, or bit mask, bit_length(value) <= bitlen.
bitlen:int bitlen:int
The effective mask length, spec. leading zeros The effective mask length, spec. leading zeros
( bitlen 4 value 1 -> 0001 ) ( bitlen 4 value 1 -> 0001 )
The bitwise expressions may look convoluted, but basically, there are The bitwise expressions may look convoluted, but basically, there are
just three parts: left-hand side, value, right-hand side. just three parts: left-hand side, value, right-hand side.
For example, say you want to insert two ones in the middle of 0b101101, For example, say you want to insert two ones in the middle of 0b101101,
@ -41,7 +41,7 @@ value is 3 (0b11) with a bit length of 2.
( 0b101101 & 0b111 ) -> 0b101. ( 0b101101 & 0b111 ) -> 0b101.
- OR that into the working 0b10111000, that is, ( 0b10111000 | 0b101 ) - OR that into the working 0b10111000, that is, ( 0b10111000 | 0b101 )
-> 0b10111101. -> 0b10111101.
To remove the center two bits of 0b101101 -> 0b1001, the process is mostly To remove the center two bits of 0b101101 -> 0b1001, the process is mostly
the same. the same.
@ -50,16 +50,16 @@ the same.
- The left shift of index produces 0b1000. - The left shift of index produces 0b1000.
- The original bint is ANDed with bitmask 0b11 producing 0b01 which is - The original bint is ANDed with bitmask 0b11 producing 0b01 which is
ORed with 0b1000 yielding the target 0b1001. ORed with 0b1000 yielding the target 0b1001.
It's not so bad once you get the hang of it. It's not so bad once you get the hang of it.
Various bit insert/remove solutions exist using bin() string functions Various bit insert/remove solutions exist using bin() string functions
and slicing, but this bitwise implementation is significantly faster and slicing, but this bitwise implementation is significantly faster
(about 3x) on Python for big ints (2^100). (about 3x) on Python for big ints (2^100).
See https://github.com/billbreit/BitWiseApps/blob/main/dev/time_ops.py See https://github.com/billbreit/BitWiseApps/blob/main/dev/time_ops.py
""" """
bit_length = int.bit_length bit_length = int.bit_length
@ -230,7 +230,6 @@ def multibit_remove(bint: int, index: int, bit_len: int) -> int:
if __name__ == "__main__": if __name__ == "__main__":
import doctest import doctest
doctest.testmod() doctest.testmod()