def decode(self, mem, addr, shift):
"""Decoding algorithm of Huffman coding.
Decode a Huffman-encoded bit string and return a decoded character.
Args:
mem (mmap): The ROM image.
addr (int): The initial address to read the variable length-bit
string.
shift (int): The initial shift bit of the address.
Returns:
An instance of tuple (addr, shift, value), where `addr` and
`shift` is the next location to read, and `value` is the
character code decoded from the Huffman tree.
"""
# Test preconditions
assert addr & 0xFF000000 == 0
assert shift & 0xFFFFFF00 == 0
huffman_on, huffman_off = self.huffman_on, self.huffman_off
node = self.huffman_root
from_cpu_addr = self.mapper.from_cpu
read_size = self.decoding_read_size
# Traverse the Huffman tree downward beginning at the root node.
while True:
# The message is a variable length-bit string.
# We take successive bits from the initial `addr`.
mem.seek(from_cpu_addr(addr))
bit = get_int(mem.read(read_size), 0, read_size) & shift
addr, shift = self._do_next_location(addr, shift)
if bit:
node = get_int(huffman_on, node, 2)
else:
node = get_int(huffman_off, node, 2)
if self._do_is_leaf_node(node):
break
node = self._do_next_node(node)
return addr, shift, node & self.decoding_mask
def test_get_int(self):
"""Test function dqutils.bit.get_int."""
targets = ((0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06),
b'\x00\x01\x02\x03\x04\x05\x06',)
for data in targets:
self.assertEqual(get_int(data, 0, 1), 0x00)
self.assertEqual(get_int(data, 1, 1), 0x01)
self.assertEqual(get_int(data, 0, 2), 0x0100)
self.assertEqual(get_int(data, 6, 2), 0x0006)
self.assertEqual(get_int(data, 0, 3), 0x020100)
self.assertEqual(get_int(data, 5, 3), 0x000605)
self.assertEqual(get_int(data, 6, 3), 0x000006)
def test_get_int_empty(self):
"""Test function dqutils.bit.get_int in case of empty value is
passed.
"""
self.assertEqual(get_int(b'', 6, 3), 0)
self.assertEqual(get_int([], 6, 3), 0)
def _do_get_value(self, byte_string):
return get_int(byte_string, self.offset, 3)
