CRC rewrite

addons/io_scene_swbf_msh/crc.py

@@ -1,15 +1,10 @@
-from struct import pack
+'''
+Based on code by Benedikt Schatz from https://github.com/Schlechtwetterfront/xsizetools/blob/master/Application/Modules/msh2_crc.py    
+''' 
 
 
-class CRCError(Exception):
-    def __init__(self, val):
-        self.val = val
-
-    def __str__(self):
-        return '{0}'.format(self.val)
-
 # CRC lookup table.
-TABLE_32 = (
+table32_lookup = (
     0x00000000, 0x04C11DB7, 0x09823B6E, 0x0D4326D9,
     0x130476DC, 0x17C56B6B, 0x1A864DB2, 0x1E475005,
     0x2608EDB8, 0x22C9F00F, 0x2F8AD6D6, 0x2B4BCB61,
@@ -76,67 +71,19 @@ TABLE_32 = (
     0xBCB4666D, 0xB8757BDA, 0xB5365D03, 0xB1F740B4
 )
 
-# Used to calculate the lowercase CRC.
-TOLOWER = (
-    0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
-    0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f,
-    0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17,
-    0x18, 0x19, 0x1a, 0x1b, 0x1c, 0x1d, 0x1e, 0x1f,
-    0x20, 0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27,
-    0x28, 0x29, 0x2a, 0x2b, 0x2c, 0x2d, 0x2e, 0x2f,
-    0x30, 0x31, 0x32, 0x33, 0x34, 0x35, 0x36, 0x37,
-    0x38, 0x39, 0x3a, 0x3b, 0x3c, 0x3d, 0x3e, 0x3f,
-    0x40, 0x61, 0x62, 0x63, 0x64, 0x65, 0x66, 0x67,
-    0x68, 0x69, 0x6a, 0x6b, 0x6c, 0x6d, 0x6e, 0x6f,
-    0x70, 0x71, 0x72, 0x73, 0x74, 0x75, 0x76, 0x77,
-    0x78, 0x79, 0x7a, 0x5b, 0x5c, 0x5d, 0x5e, 0x5f,
-    0x60, 0x61, 0x62, 0x63, 0x64, 0x65, 0x66, 0x67,
-    0x68, 0x69, 0x6a, 0x6b, 0x6c, 0x6d, 0x6e, 0x6f,
-    0x70, 0x71, 0x72, 0x73, 0x74, 0x75, 0x76, 0x77,
-    0x78, 0x79, 0x7a, 0x7b, 0x7c, 0x7d, 0x7e, 0x7f,
-    0x80, 0x81, 0x82, 0x83, 0x84, 0x85, 0x86, 0x87,
-    0x88, 0x89, 0x8a, 0x8b, 0x8c, 0x8d, 0x8e, 0x8f,
-    0x90, 0x91, 0x92, 0x93, 0x94, 0x95, 0x96, 0x97,
-    0x98, 0x99, 0x9a, 0x9b, 0x9c, 0x9d, 0x9e, 0x9f,
-    0xa0, 0xa1, 0xa2, 0xa3, 0xa4, 0xa5, 0xa6, 0xa7,
-    0xa8, 0xa9, 0xaa, 0xab, 0xac, 0xad, 0xae, 0xaf,
-    0xb0, 0xb1, 0xb2, 0xb3, 0xb4, 0xb5, 0xb6, 0xb7,
-    0xb8, 0xb9, 0xba, 0xbb, 0xbc, 0xbd, 0xbe, 0xbf,
-    0xc0, 0xc1, 0xc2, 0xc3, 0xc4, 0xc5, 0xc6, 0xc7,
-    0xc8, 0xc9, 0xca, 0xcb, 0xcc, 0xcd, 0xce, 0xcf,
-    0xd0, 0xd1, 0xd2, 0xd3, 0xd4, 0xd5, 0xd6, 0xd7,
-    0xd8, 0xd9, 0xda, 0xdb, 0xdc, 0xdd, 0xde, 0xdf,
-    0xe0, 0xe1, 0xe2, 0xe3, 0xe4, 0xe5, 0xe6, 0xe7,
-    0xe8, 0xe9, 0xea, 0xeb, 0xec, 0xed, 0xee, 0xef,
-    0xf0, 0xf1, 0xf2, 0xf3, 0xf4, 0xf5, 0xf6, 0xf7,
-    0xf8, 0xf9, 0xfa, 0xfb, 0xfc, 0xfd, 0xfe, 0xff
-)
 
+def to_lower(charcode):
+    if charcode <= 64 or charcode > 90:
+        return charcode
+    else:
+        return charcode + 32
 
-def return_lowest_bits(n):
-    '''Simulate unsigned behavior.'''
-    return n & 0xFFFFFFFF
-
-
-def crc(string):
-    '''Calculate the Zero CRC from string and return it as number.'''
-    crc_ = 0
-    crc_ = return_lowest_bits(~crc_)
+# Not sure what Schlechtwetterfront means by "Simulate unsigned behavior.",
+# kept it anyways just without the extra functions
+def to_crc(string):
+    crc_ = ~0 & 0xFFFFFFFF
     if string:
         for char in string:
-            ind = (crc_ >> 24)
-            ind = ind ^ TOLOWER[ord(char)]
-            crc_ = return_lowest_bits(crc_ << 8) ^ TABLE_32[ind]
-    return return_lowest_bits(~crc_)
-
-
-def strcrc(string):
-    '''Calculate the Zero CRC and return it in a structure
-    usable in .msh files.'''
-    return pack('<I', crc(string))
-
-
-def compare_crc_adv(possible_strings, crc_):
-    for string in possible_strings:
-        if crc_ == strcrc(string):
-            return string
+            ind = (crc_ >> 24) ^ to_lower(ord(char))
+            crc_ = ((crc_ << 8) & 0xFFFFFFFF) ^ table32_lookup[ind]
+    return ~crc_ & 0xFFFFFFFF