Merge Max's code for System 7 resource compression
This commit is contained in:
Elliot Nunn
commit
cfc55b63f0
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'''
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This script implements the GreggyBits decompression algorithm
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found in the 'dcmp' 2 resource.
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'''
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import struct
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# predefined lookup table of the most frequent words
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GreggDefLUT = (
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0x0000, 0x0008, 0x4EBA, 0x206E, 0x4E75, 0x000C, 0x0004, 0x7000,
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0x0010, 0x0002, 0x486E, 0xFFFC, 0x6000, 0x0001, 0x48E7, 0x2F2E,
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0x4E56, 0x0006, 0x4E5E, 0x2F00, 0x6100, 0xFFF8, 0x2F0B, 0xFFFF,
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0x0014, 0x000A, 0x0018, 0x205F, 0x000E, 0x2050, 0x3F3C, 0xFFF4,
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0x4CEE, 0x302E, 0x6700, 0x4CDF, 0x266E, 0x0012, 0x001C, 0x4267,
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0xFFF0, 0x303C, 0x2F0C, 0x0003, 0x4ED0, 0x0020, 0x7001, 0x0016,
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0x2D40, 0x48C0, 0x2078, 0x7200, 0x588F, 0x6600, 0x4FEF, 0x42A7,
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0x6706, 0xFFFA, 0x558F, 0x286E, 0x3F00, 0xFFFE, 0x2F3C, 0x6704,
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0x598F, 0x206B, 0x0024, 0x201F, 0x41FA, 0x81E1, 0x6604, 0x6708,
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0x001A, 0x4EB9, 0x508F, 0x202E, 0x0007, 0x4EB0, 0xFFF2, 0x3D40,
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0x001E, 0x2068, 0x6606, 0xFFF6, 0x4EF9, 0x0800, 0x0C40, 0x3D7C,
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0xFFEC, 0x0005, 0x203C, 0xFFE8, 0xDEFC, 0x4A2E, 0x0030, 0x0028,
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0x2F08, 0x200B, 0x6002, 0x426E, 0x2D48, 0x2053, 0x2040, 0x1800,
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0x6004, 0x41EE, 0x2F28, 0x2F01, 0x670A, 0x4840, 0x2007, 0x6608,
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0x0118, 0x2F07, 0x3028, 0x3F2E, 0x302B, 0x226E, 0x2F2B, 0x002C,
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0x670C, 0x225F, 0x6006, 0x00FF, 0x3007, 0xFFEE, 0x5340, 0x0040,
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0xFFE4, 0x4A40, 0x660A, 0x000F, 0x4EAD, 0x70FF, 0x22D8, 0x486B,
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0x0022, 0x204B, 0x670E, 0x4AAE, 0x4E90, 0xFFE0, 0xFFC0, 0x002A,
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0x2740, 0x6702, 0x51C8, 0x02B6, 0x487A, 0x2278, 0xB06E, 0xFFE6,
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0x0009, 0x322E, 0x3E00, 0x4841, 0xFFEA, 0x43EE, 0x4E71, 0x7400,
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0x2F2C, 0x206C, 0x003C, 0x0026, 0x0050, 0x1880, 0x301F, 0x2200,
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0x660C, 0xFFDA, 0x0038, 0x6602, 0x302C, 0x200C, 0x2D6E, 0x4240,
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0xFFE2, 0xA9F0, 0xFF00, 0x377C, 0xE580, 0xFFDC, 0x4868, 0x594F,
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0x0034, 0x3E1F, 0x6008, 0x2F06, 0xFFDE, 0x600A, 0x7002, 0x0032,
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0xFFCC, 0x0080, 0x2251, 0x101F, 0x317C, 0xA029, 0xFFD8, 0x5240,
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0x0100, 0x6710, 0xA023, 0xFFCE, 0xFFD4, 0x2006, 0x4878, 0x002E,
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0x504F, 0x43FA, 0x6712, 0x7600, 0x41E8, 0x4A6E, 0x20D9, 0x005A,
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0x7FFF, 0x51CA, 0x005C, 0x2E00, 0x0240, 0x48C7, 0x6714, 0x0C80,
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0x2E9F, 0xFFD6, 0x8000, 0x1000, 0x4842, 0x4A6B, 0xFFD2, 0x0048,
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0x4A47, 0x4ED1, 0x206F, 0x0041, 0x600C, 0x2A78, 0x422E, 0x3200,
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0x6574, 0x6716, 0x0044, 0x486D, 0x2008, 0x486C, 0x0B7C, 0x2640,
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0x0400, 0x0068, 0x206D, 0x000D, 0x2A40, 0x000B, 0x003E, 0x0220
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)
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def EncodeMaskedWords(src, dst, pos, n, tab):
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mask = 0
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encoded = bytearray()
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for rPos in range(n):
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mask <<= 1
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word = src[pos+rPos]
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compressed = 1 if word in tab else 0
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mask |= compressed
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if compressed: # replace word with table index
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encoded.append(tab.index(word))
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else: # otherwise, just copy unencoded data over
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encoded.extend(word.to_bytes(2, 'big'))
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if n < 8: # left-justify the mask for n < 8
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mask <<= 8 - n
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dst.append(mask)
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dst.extend(encoded)
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return pos+n
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def DecodeMaskedWords(src, dst, pos, n, tab, mask):
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'''Decode n words using the specified lookup table under control of mask.
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Return new bitstream position.
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'''
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if mask == 0: # all mask bits are zero?
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nBytes = n * 2
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dst.extend(src[pos:pos+nBytes]) # copy over n*2 bytes
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pos += nBytes
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else:
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for bn in range(7, 7 - n, -1):
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if mask & (1 << bn): # mask bit set?
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word = tab[src[pos]] # decode next word with LUT
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dst.extend(word.to_bytes(2, 'big')) # write it to dst
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pos += 1
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else: # otherwise, copy over that word
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dst.extend(src[pos:pos+2])
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pos += 2
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return pos
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def GreggDecompress(src, dst, unpackSize, pos=0):
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'''Decompress resource data from src to dst.
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Parameters:
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src source buffer containing compressed data
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dst destination buffer, must be bytearray to work properly
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unpackSize size in bytes of the unpacked resource data
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pos offset to my Gregg-specific buffer in src
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'''
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_dcmp, _slop, tabSize, comprFlags = struct.unpack_from(">HHBB", src, pos)
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pos += 6
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hasDynamicTab = comprFlags & 1
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isBitmapped = comprFlags & 2
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# print("tabSize: %d" % tabSize)
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# print("comprFlags: 0x%X, dynamic table: %s, bitmap data: %s" % (comprFlags,
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# "yes" if hasDynamicTab else "no", "yes" if isBitmapped else "no"))
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if hasDynamicTab:
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nEntries = tabSize + 1
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dynamicLUT = struct.unpack_from(">" + str(nEntries) + "H", src, pos)
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pos += nEntries * 2
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# dump dynamic LUT
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if 0:
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for idx, elem in enumerate(dynamicLUT):
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if idx and not idx & 3:
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print(",")
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else:
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print(", ", end="")
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print("0x%04X" % elem, end="")
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print("")
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LUT = dynamicLUT if hasDynamicTab else GreggDefLUT
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nWords = unpackSize >> 1
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hasExtraByte = unpackSize & 1
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if isBitmapped:
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nRuns = nWords >> 3
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for idx in range(nRuns):
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mask = src[pos]
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pos += 1
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#print("Mask for run #%d: 0x%X" % (idx, bitmap))
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pos = DecodeMaskedWords(src, dst, pos, 8, LUT, mask)
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if nWords & 7:
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trailingWords = nWords & 7
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lastMask = src[pos]
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pos += 1
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#print("Last mask: 0x%X, trailing words: %d" % (lastMask, trailingWords))
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pos = DecodeMaskedWords(src, dst, pos, trailingWords, LUT, lastMask)
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else:
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for i in range(nWords):
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word = LUT[src[pos]] # decode next word with LUT
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dst.extend(word.to_bytes(2, 'big')) # write it to dst
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pos += 1
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if hasExtraByte: # have a got an extra byte at the end?
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dst.append(src[pos]) # copy it over
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pos += 1
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#print("Last input position: %d" % pos)
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def GreggCompress(src, dst, customTab='auto', isBitmapped='auto'):
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# future addition
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customTab = True # so the big code path gets tested!
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isBitmapped = True # required for now
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if customTab: # calculate, and if necessary, resolve 'auto'
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# convert input bytes into an array of words
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nWords = len(src) >> 1
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inWords = struct.unpack(">" + str(nWords) + "H", src[:nWords*2])
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# count occurence of each word
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from collections import Counter
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wordsCounts = Counter(inWords)
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# grab word counts in descending order (most frequent comes first)
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sortedCounts = list(set(wordsCounts.values()))
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sortedCounts.sort(reverse=True)
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# now we're ready to construct a table of 256 most common words
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embeddedTab = list()
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nElems = 0
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for cnt in sortedCounts:
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# pick all words for a specific count and sort them in descending order
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words = [key for (key, value) in wordsCounts.items() if value == cnt]
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words.sort(reverse=True)
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# append them to the table, stop when tableMax is reached
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if nElems + len(words) < 256:
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embeddedTab.extend(words)
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nElems += len(words)
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else:
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remainedElems = 256 - nElems
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embeddedTab.extend(words[:remainedElems])
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nElems += remainedElems
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if nElems >= 256:
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break
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if 0: # dump the resulting table
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for idx, elem in enumerate(embeddedTab):
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if idx and not idx & 3:
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print(",")
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else:
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print(", ", end="")
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print("0x%04X" % elem, end="")
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print("")
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# here, decide whether 'auto' customTab should be on or off!
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# write out the header
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isBitmapped = True # will need to resolve this later
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flags = customTab * 1 + isBitmapped * 2
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dst.extend(struct.pack(">HHBB", 2, 0, len(embeddedTab)-1, flags))
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if customTab:
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# write the constructed table into output
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for word in embeddedTab:
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dst.extend(word.to_bytes(2, 'big'))
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if isBitmapped:
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pos = 0
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nRuns = nWords >> 3
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for idx in range(nRuns):
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pos = EncodeMaskedWords(inWords, dst, pos, 8, embeddedTab)
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if nWords & 7:
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pos = EncodeMaskedWords(inWords, dst, pos, nWords & 7, embeddedTab)
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if len(src) & 1: # copy over last byte in the case of odd length
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dst.append(src[-1])
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else:
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raise ValueError("Non-bitmapped compression not yet implemented")
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@ -0,0 +1,65 @@
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'''
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Handling of compressed MacOS resources.
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Author: Max Poliakovski 2018
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'''
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import struct
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from .GreggBits import GreggDecompress, GreggCompress
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def GetEncoding(dat):
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sig, hdrlen, vers, attrs, biglen = struct.unpack_from(">IHBBI", dat)
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if sig != 0xA89F6572:
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# print("Invalid extended resource header sig: 0x%X" % sig)
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return 'UnknownCompression'
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if vers not in (8, 9):
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# print("Unknown ext res header format: %d" % vers)
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return 'UnknownCompression'
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if attrs & 1 == 0:
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# print("extAttributes,bit0 isn't set. Treat this res as uncompressed.")
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return 'UnknownCompression'
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# print("Uncompressed length: %d" % biglen)
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if vers == 8:
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return 'UnknownCompression' # return 'DonnBits'
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elif vers == 9:
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if dat[12:14] == b'\x00\x02':
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return 'GreggyBits'
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else:
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return 'UnknownCompression'
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else:
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return 'UnknownCompression'
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def DecompressResource(dat):
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encoding = GetEncoding(dat)
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sig, hdrlen, vers, attrs, biglen = struct.unpack_from(">IHBBI", dat)
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if encoding == 'DonnBits':
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raise NotImplementedError('DonnBits')
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elif encoding == 'GreggyBits':
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dst = bytearray()
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GreggDecompress(dat, dst, unpackSize=biglen, pos=12)
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return bytes(dst)
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elif encoding == 'UnknownCompression':
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return dat # passthru
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def CompressResource(dat, encoding):
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if encoding == 'UnknownCompression':
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return dat
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elif encoding == 'GreggyBits':
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dst = bytearray()
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# re-create extended resource header
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dst.extend([0xA8, 0x9F, 0x65, 0x72, 0x00, 0x12, 0x09, 0x01])
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dst.extend(len(dat).to_bytes(4, 'big'))
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# leave Gregg-specific header to the compressor
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GreggCompress(dat, dst)
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return bytes(dst)
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@ -2,7 +2,7 @@ import collections
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import struct
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import enum
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import re
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from ResDecompress import DecompressResource, CompressResource, GetEncoding
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from .compression import DecompressResource, CompressResource, GetEncoding
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FAKE_HEADER_RSRC_TYPE = b'header' # obviously invalid
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2
setup.py
2
setup.py
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@ -17,6 +17,6 @@ setup(
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'Topic :: System :: Filesystems',
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'Development Status :: 3 - Alpha',
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],
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packages=['macresources', 'ResDecompress'],
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packages=['macresources'],
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scripts=['bin/SimpleRez', 'bin/SimpleDeRez'],
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)
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@ -0,0 +1,13 @@
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from .macresources.compression import GetEncoding, DecompressResource, CompressResource
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def compress_then_extract(dat, encoding):
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a = CompressResource(dat, encoding);
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if encoding != 'UnknownCompression': assert a.startswith(b'\xA8\x9F\x65\x72')
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assert GetEncoding(a) == encoding
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b = DecompressResource(a)
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assert b == dat
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def test_all():
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for enc in ['GreggyBits', 'UnknownCompression']:
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compress_then_extract(bytes(100), encoding=enc)
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compress_then_extract(b'The quick brown fox jumps over the lazy dog', encoding=enc)
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