def _words_to_block(words):
if not isinstance(words, tuple):
raise TypeError("expected tuple of words")
if len(words) == 0:
raise ValueError("no words in block")
if len(words) > 3:
raise ValueError("too many words in block")
try:
indices = list(word_to_index(word) for word in words)
except KeyError as e:
raise ValueError("word not recognized") from e
# calculate length of block.
# both three byte and four byte blocks map to three words but can be
# distinguished as a different word list is used to encode the last word
# in the three byte case
length = {
1: 1,
2: 2,
3: 3 if indices[-1] >= 1626 else 4,
}[len(words)]
if length == 3:
indices[2] -= 1626
# check that words in the second word list don't appear anywhere else in
# the block
for index in indices:
if index > 1626:
raise ValueError(
"unexpected three byte word: %s" % index_to_word(index)
)
num = _from_base(1626, reversed(indices))
block = bytes(reversed(_to_base(256, num)))
# pad to correct length
return block.ljust(length, b'\x00')
def _words_to_block(words):
if not isinstance(words, tuple):
raise TypeError("expected tuple of words")
if len(words) == 0:
raise ValueError("no words in block")
if len(words) > 3:
raise ValueError("too many words in block")
try:
indices = list(word_to_index(word) for word in words)
except KeyError as e:
raise ValueError("word not recognized") from e
# Calculate length of block.
# Both three byte and four byte blocks map to three words but can be
# distinguished as a different word list is used to encode the last word
# in the three byte case.
length = {
1: 1,
2: 2,
3: 3 if indices[-1] >= 1626 else 4,
}[len(words)]
if length == 3:
indices[2] -= 1626
# Check that words in the second word list don't appear anywhere else in
# the block.
for index in indices:
if index > 1626:
raise ValueError((
"unexpected three byte word: {word!r}"
).format(word=index_to_word(index)))
num = from_base(1626, reversed(indices))
block = bytes(reversed(to_base(256, num)))
# Pad to correct length.
return block.ljust(length, b'\x00')
def _block_to_words(block):
for i in _block_to_indices(block):
yield index_to_word(i)
def _block_to_words(block):
for i in _block_to_indices(block):
yield index_to_word(i)
