mbirth/gcd-parser
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Further optimisations in ChkSum.

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This commit is contained in:
Markus Birth 2018-10-16 23:44:30 +02:00
parent 155d0e023c
commit 0c9528fd4f
Signed by: mbirth
GPG Key ID: A9928D7A098C3A9A
1 changed files with 3 additions and 6 deletions
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9
grmn/chksum.py
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@ -4,16 +4,12 @@ class ChkSum:
def __init__(self): def __init__(self):
self.chksum = 0 self.chksum = 0
self.chksum_without_last = 0
self.last_byte = 0xff self.last_byte = 0xff
def add(self, data): def add(self, data):
for c in data[:-1]: for c in data:
self.chksum += c self.chksum += c
self.chksum_without_last = self.chksum
self.chksum_without_last &= 0xff
self.last_byte = data[-1] self.last_byte = data[-1]
self.chksum += self.last_byte
self.chksum &= 0xff self.chksum &= 0xff
def add_from_file(self, filename: str, print_progress: bool = False, blocksize: int=16384): def add_from_file(self, filename: str, print_progress: bool = False, blocksize: int=16384):
@ -38,7 +34,8 @@ class ChkSum:
return (self.chksum == 0) return (self.chksum == 0)
def get_expected(self): def get_expected(self):
expected = ( 0x100 - self.chksum_without_last ) & 0xff chksum_without_last = ( 0x100 + self.chksum - self.last_byte ) & 0xff
expected = ( 0x100 - chksum_without_last ) & 0xff
return expected return expected
def get_last_byte(self): def get_last_byte(self):