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algorithms: generate table on init #10

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Merged
tpircher merged 1 commit into from
Aug 16, 2025
Merged

algorithms: generate table on init #10

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8 changes: 4 additions & 4 deletions src/pycrc/algorithms.py
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Original file line number Diff line number Diff line change
Expand Up @@ -91,6 +91,8 @@ def __init__(self, width, poly, reflect_in, xor_in, reflect_out, xor_out,
else:
self.crc_shift = 0

self.tbl = self.gen_table()

def __get_nondirect_init(self, init):
"""
return the non-direct init if the direct algorithm has been selected.
Expand Down Expand Up @@ -211,20 +213,18 @@ def table_driven(self, in_data):
if isinstance(in_data, str):
in_data = bytearray(in_data, 'utf-8')

tbl = self.gen_table()

if not self.reflect_in:
reg = self.direct_init << self.crc_shift
for octet in in_data:
tblidx = ((reg >> (self.width - self.tbl_idx_width + self.crc_shift)) ^ octet) & 0xff
reg = ((reg << (self.tbl_idx_width - self.crc_shift)) ^
(tbl[0][tblidx] << self.crc_shift)) & (self.mask << self.crc_shift)
(self.tbl[0][tblidx] << self.crc_shift)) & (self.mask << self.crc_shift)
reg = reg >> self.crc_shift
else:
reg = self.reflect(self.direct_init, self.width)
for octet in in_data:
tblidx = (reg ^ octet) & 0xff
reg = ((reg >> self.tbl_idx_width) ^ tbl[0][tblidx]) & self.mask
reg = ((reg >> self.tbl_idx_width) ^ self.tbl[0][tblidx]) & self.mask
reg = self.reflect(reg, self.width) & self.mask

if self.reflect_out:
Expand Down