macresources/GreggDecompress.py

'''
    This script implements the GreggyBits decompression algorithm
    found in the 'dcmp' 2 resource.
'''

import struct

# predefined lookup table of the most frequent words
GreggDefLUT = (
    0x0000, 0x0008, 0x4EBA, 0x206E, 0x4E75, 0x000C, 0x0004, 0x7000,
    0x0010, 0x0002, 0x486E, 0xFFFC, 0x6000, 0x0001, 0x48E7, 0x2F2E,
    0x4E56, 0x0006, 0x4E5E, 0x2F00, 0x6100, 0xFFF8, 0x2F0B, 0xFFFF,
    0x0014, 0x000A, 0x0018, 0x205F, 0x000E, 0x2050, 0x3F3C, 0xFFF4,
    0x4CEE, 0x302E, 0x6700, 0x4CDF, 0x266E, 0x0012, 0x001C, 0x4267,
    0xFFF0, 0x303C, 0x2F0C, 0x0003, 0x4ED0, 0x0020, 0x7001, 0x0016,
    0x2D40, 0x48C0, 0x2078, 0x7200, 0x588F, 0x6600, 0x4FEF, 0x42A7,
    0x6706, 0xFFFA, 0x558F, 0x286E, 0x3F00, 0xFFFE, 0x2F3C, 0x6704,
    0x598F, 0x206B, 0x0024, 0x201F, 0x41FA, 0x81E1, 0x6604, 0x6708,
    0x001A, 0x4EB9, 0x508F, 0x202E, 0x0007, 0x4EB0, 0xFFF2, 0x3D40,
    0x001E, 0x2068, 0x6606, 0xFFF6, 0x4EF9, 0x0800, 0x0C40, 0x3D7C,
    0xFFEC, 0x0005, 0x203C, 0xFFE8, 0xDEFC, 0x4A2E, 0x0030, 0x0028,
    0x2F08, 0x200B, 0x6002, 0x426E, 0x2D48, 0x2053, 0x2040, 0x1800,
    0x6004, 0x41EE, 0x2F28, 0x2F01, 0x670A, 0x4840, 0x2007, 0x6608,
    0x0118, 0x2F07, 0x3028, 0x3F2E, 0x302B, 0x226E, 0x2F2B, 0x002C,
    0x670C, 0x225F, 0x6006, 0x00FF, 0x3007, 0xFFEE, 0x5340, 0x0040,
    0xFFE4, 0x4A40, 0x660A, 0x000F, 0x4EAD, 0x70FF, 0x22D8, 0x486B,
    0x0022, 0x204B, 0x670E, 0x4AAE, 0x4E90, 0xFFE0, 0xFFC0, 0x002A,
    0x2740, 0x6702, 0x51C8, 0x02B6, 0x487A, 0x2278, 0xB06E, 0xFFE6,
    0x0009, 0x322E, 0x3E00, 0x4841, 0xFFEA, 0x43EE, 0x4E71, 0x7400,
    0x2F2C, 0x206C, 0x003C, 0x0026, 0x0050, 0x1880, 0x301F, 0x2200,
    0x660C, 0xFFDA, 0x0038, 0x6602, 0x302C, 0x200C, 0x2D6E, 0x4240,
    0xFFE2, 0xA9F0, 0xFF00, 0x377C, 0xE580, 0xFFDC, 0x4868, 0x594F,
    0x0034, 0x3E1F, 0x6008, 0x2F06, 0xFFDE, 0x600A, 0x7002, 0x0032,
    0xFFCC, 0x0080, 0x2251, 0x101F, 0x317C, 0xA029, 0xFFD8, 0x5240,
    0x0100, 0x6710, 0xA023, 0xFFCE, 0xFFD4, 0x2006, 0x4878, 0x002E,
    0x504F, 0x43FA, 0x6712, 0x7600, 0x41E8, 0x4A6E, 0x20D9, 0x005A,
    0x7FFF, 0x51CA, 0x005C, 0x2E00, 0x0240, 0x48C7, 0x6714, 0x0C80,
    0x2E9F, 0xFFD6, 0x8000, 0x1000, 0x4842, 0x4A6B, 0xFFD2, 0x0048,
    0x4A47, 0x4ED1, 0x206F, 0x0041, 0x600C, 0x2A78, 0x422E, 0x3200,
    0x6574, 0x6716, 0x0044, 0x486D, 0x2008, 0x486C, 0x0B7C, 0x2640,
    0x0400, 0x0068, 0x206D, 0x000D, 0x2A40, 0x000B, 0x003E, 0x0220
)


def DecodeMaskedWords(src, dst, pos, n, tab, mask):
    '''Decode n words using the specified lookup table under control of mask.
       Return new bitstream position.
    '''
    if mask == 0: # all mask bits are zero?
        nBytes = n * 2
        dst.extend(src[pos:pos+nBytes]) # copy over n*2 bytes
        pos += nBytes
    else:
        for bn in range(7, 7 - n, -1):
            if mask & (1 << bn): # mask bit set?
                word = tab[src[pos]] # decode next word with LUT
                dst.extend(word.to_bytes(2, 'big')) # write it to dst
                pos += 1
            else: # otherwise, copy over that word
                dst.extend(src[pos:pos+2])
                pos += 2
    return pos


def GreggDecompress(src, dst, unpackSize, tabSize, comprFlags):
    '''Decompress resource data from src to dst.

       Parameters:
       src          source buffer containing compressed data
       dst          destination buffer, must be bytearray to work properly
       unpackSize   size in bytes of the unpacked resource data
       tabSize      size of the embedded lookup table
       comprFlags   compression flags from the extended resource header
    '''
    hasDynamicTab = comprFlags & 1
    isBitmapped   = comprFlags & 2
    print("tabSize: %d" % tabSize)
    print("comprFlags: 0x%X, dynamic table: %s, bitmap data: %s" % (comprFlags,
          "yes" if hasDynamicTab else "no", "yes" if isBitmapped else "no"))

    if hasDynamicTab:
        nEntries = tabSize + 1
        pos = nEntries * 2
        dynamicLUT = struct.unpack(">" + str(nEntries) + "H", src[:pos])
        # dump dynamic LUT
        if 0:
            for idx, elem in enumerate(dynamicLUT):
                if idx and not idx & 3:
                    print(",")
                else:
                    print(", ", end="")
                print("0x%04X" % elem, end="")
            print("")
    else:
        pos = 0

    LUT = dynamicLUT if hasDynamicTab else GreggDefLUT
    nWords = unpackSize >> 1
    hasExtraByte = unpackSize & 1

    if isBitmapped:
        nRuns = nWords >> 3
        for idx in range(nRuns):
            mask = src[pos]
            pos += 1
            #print("Mask for run #%d: 0x%X" % (idx, bitmap))

            pos = DecodeMaskedWords(src, dst, pos, 8, LUT, mask)

        if nWords & 7:
            trailingWords = nWords & 7
            lastMask = src[pos]
            pos += 1
            #print("Last mask: 0x%X, trailing words: %d" % (lastMask, trailingWords))
            pos = DecodeMaskedWords(src, dst, pos, trailingWords, LUT, lastMask)
    else:
        for i in range(nWords):
            word = LUT[src[pos]] # decode next word with LUT
            dst.extend(word.to_bytes(2, 'big')) # write it to dst
            pos += 1

    if hasExtraByte: # have a got an extra byte at the end?
        dst.expand(src[pos]) # copy it over
        pos += 1

    #print("Last input position: %d" % pos)