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 from .py3compat import int2byte def int_to_bin(number, width=32): r""" Convert an integer into its binary representation in a bytes object. Width is the amount of bits to generate. If width is larger than the actual amount of bits required to represent number in binary, sign-extension is used. If it's smaller, the representation is trimmed to width bits. Each "bit" is either '\x00' or '\x01'. The MSBit is first. Examples: >>> int_to_bin(19, 5) b'\x01\x00\x00\x01\x01' >>> int_to_bin(19, 8) b'\x00\x00\x00\x01\x00\x00\x01\x01' """ if number < 0: number += 1 << width i = width - 1 bits = bytearray(width) while number and i >= 0: bits[i] = number & 1 number >>= 1 i -= 1 return bytes(bits) _bit_values = { 0: 0, 1: 1, 48: 0, # '0' 49: 1, # '1' # The following are for Python 2, in which iteration over a bytes object # yields single-character bytes and not integers. '\x00': 0, '\x01': 1, '0': 0, '1': 1, } def bin_to_int(bits, signed=False): r""" Logical opposite of int_to_bin. Both '0' and '\x00' are considered zero, and both '1' and '\x01' are considered one. Set sign to True to interpret the number as a 2-s complement signed integer. """ number = 0 bias = 0 ptr = 0 if signed and _bit_values[bits[0]] == 1: bits = bits[1:] bias = 1 << len(bits) for b in bits: number <<= 1 number |= _bit_values[b] return number - bias def swap_bytes(bits, bytesize=8): r""" Bits is a b'' object containing a binary representation. Assuming each bytesize bits constitute a bytes, perform a endianness byte swap. Example: >>> swap_bytes(b'00011011', 2) b'11100100' """ i = 0 l = len(bits) output = [b""] * ((l // bytesize) + 1) j = len(output) - 1 while i < l: output[j] = bits[i : i + bytesize] i += bytesize j -= 1 return b"".join(output) _char_to_bin = {} _bin_to_char = {} for i in range(256): ch = int2byte(i) bin = int_to_bin(i, 8) # Populate with for both keys i and ch, to support Python 2 & 3 _char_to_bin[ch] = bin _char_to_bin[i] = bin _bin_to_char[bin] = ch def encode_bin(data): """ Create a binary representation of the given b'' object. Assume 8-bit ASCII. Example: >>> encode_bin('ab') b"\x00\x01\x01\x00\x00\x00\x00\x01\x00\x01\x01\x00\x00\x00\x01\x00" """ return b"".join(_char_to_bin[ch] for ch in data) def decode_bin(data): """ Locical opposite of decode_bin. """ if len(data) & 7: raise ValueError("Data length must be a multiple of 8") i = 0 j = 0 l = len(data) // 8 chars = [b""] * l while j < l: chars[j] = _bin_to_char[data[i:i+8]] i += 8 j += 1 return b"".join(chars)