![]() As should be expected from the quote above about "the illusion of an infinite string of sign bits extending to the left," a negative number throws the computer into an infinite loop. The only method generally applicable to Python integers of unknown magnitude is the "obvious way" of counting the number of bitwise shift operations needed to reduce the input to 0.īitLen() counts the actual bit length of a Python integer, that is, the number of the highest non-zero bit plus 1. The section "Finding integer log base 2 of an integer" on the "Bit Twiddling Hacks"(ref.1) web page includes a number of methods for determining this value for integers of known magnitude, presumably when no math coprocessor is available. log( int_type, 2))Īn input less than or equal to 0 results in a " ValueError: math domain error" * There is a long discussion on this topic, and why this method is not good, in "Issue 3439" at : This discussion led up to the addition of bit_length() in Python 3.1.ġ import math 2 3 hiBit = math. In versions before 3.1, the easiest way to determine the highest bit set is*: ![]() ![]() This is the same as the exponent of the floating point representation of the integer, and is also called its "integer log base 2".(ref.1) The number of the highest bit set is the highest power of 2 less than or equal to the input integer. Unless you know you are working with numbers that are less than a certain length, for instance numbers from arrays of integers, shifts, rotations, etc. Python 3.1 adds a bit_length() method to the int type that does exactly that. Prior to Python 3.1, there was no easy way to determine how Python represented a specific integer internally, i.e. For the purpose of shift and mask operations, a binary representation is assumed, and negative numbers are represented in a variant of 2’s complement which gives the illusion of an infinite string of sign bits extending to the left." "Integers (int) These represent numbers in an unlimited range, subject to available (virtual) memory only. Some simple code is at ASPN: bit-field manipulation.ġ def bin( s): 2 return str( s) if s> 1) + str( s& 1)įrom "The Python Language Reference" page on the Data Model: Google Project Hostingīitstruct - This module performs conversions between Python values and C bit field structs represented as Python bytearrays. Python-bitstring - A Python module to help you manage your bits. Apply operations in block groupings: ex: apply XOR 10101 (5 bits) repeatedly across a field.Ĭtypes - A foreign function library for Python - Python v2.7.3 documentation - part of the standard libraryīitarray - efficient arrays of booleans - C extension. ![]() Switch Endianness, with different block sizes.Similarly, revert regions of bits, apply logic to regions of bits, etc.That is, say: "rotate bits 13-17, wrapping around the edges," or, "rotate bits 13-17, lose bits on the one side, set all new bits to 0." Turn "11011000111101." into bytes, (padded left or right, 0 or 1,) and vice versa.Here is some information and goals related to Python bit manipulation, binary manipulation.
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