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Slight optimization of python lz77 code.

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This commit is contained in:
Jennifer Taylor 2020-12-20 04:06:41 +00:00
parent c431e30d3b
commit e70b74f21a
1 changed files with 20 additions and 14 deletions
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34
bemani/protocol/lz77.py
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@ -356,7 +356,7 @@ class Lz77Compress:
start_write_size = self.bytes_written
self.__ring_write(index)
copy_amount = 3
while copy_amount < (backref_amount):
while copy_amount < backref_amount:
# First, let's see if we have any 3-wide chunks to consume.
index = self.data[(self.read_pos + copy_amount):(self.read_pos + copy_amount + 3)]
locations = self.starts[index]
@ -373,21 +373,27 @@ class Lz77Compress:
else:
# Check our existing locations to figure out if we still have
# longest prefixes of 1 or 2 left.
locations = self.locations[self.data[self.read_pos + copy_amount]]
new_backref_locations = [
absolute_pos for absolute_pos in possible_backref_locations
if absolute_pos + copy_amount in locations
]
while copy_amount < backref_amount:
locations = self.locations[self.data[self.read_pos + copy_amount]]
new_backref_locations = [
absolute_pos for absolute_pos in possible_backref_locations
if absolute_pos + copy_amount in locations
]
# If we have no longest prefixes, that means that any of the
# previous prefixes are good enough.
if not new_backref_locations:
break
# If we have no longest prefixes, that means that any of the
# previous prefixes are good enough.
if not new_backref_locations:
break
# Mark that we're copying an extra byte from the backref.
self.__ring_write(self.data[(self.read_pos + copy_amount):(self.read_pos + copy_amount + 1)])
copy_amount += 1
possible_backref_locations = new_backref_locations
# Mark that we're copying an extra byte from the backref.
self.__ring_write(self.data[(self.read_pos + copy_amount):(self.read_pos + copy_amount + 1)])
copy_amount += 1
possible_backref_locations = new_backref_locations
# Either we looped above in the inner while, or we didn't. Either way,
# we don't have any more to check since there were no more 3-long backref
# locations.
break
# Now that we have a list of candidates, arbitrarily pick the
# first one as our candidate and output it.