Need help in compression algorithm identification

Question

Not quite sure that this is a StackOveflow question, but however.

Currently I'm in reversing an old MS-DOS Neuromancer game (Interplay Productions, 1988. Based on William Gibson's novel). For now I have already written an utility that parses game resources and extracts sprites. Sprites are bitmaps that compressed with some fancy algorithm. I have restored that algorithm by porting it's 16-bit disassembly to 64-bit assembly (I'm working on Windows 10 and using MASM in MSVS 2017). It results in ~800 lines of pretty obfuscated assembly (which became even more obfuscated after porting it to 64-bit) that works and I'm about rewriting it in plain old C. However it makes no sense because i can't identify an actual algorithm.

And here is the problem. I assume that the game uses some widly known data compression algorithm. I will provide an example by posting chunks of data that are observable during the decompression process. I hope that there are some compression experts who will recognize the algorithm (if my theory about "widly known algorithm" is correct). Thank you in advance!

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Here we go, decompressing CURSORS.IMH file that contains a series of bitmaps that shows diffrent in-game cursors: SRC: Initial data, 211 bytes stored in 512 byte buffer: 0x0000 3f 01 00 00 04 40 7e ec d0 c2 2d 0a 46 a3 3f f2 0x0010 71 11 62 30 64 0e 10 4c e0 c5 85 05 fc ff 50 01 0x0020 04 c0 26 0f e2 c0 85 c2 50 17 fa 05 54 b0 6c 2d 0x0030 74 13 e9 c7 45 1d d8 b6 2c 18 e7 14 7b 8b d7 9b 0x0040 bb e5 eb 60 4d 2f ef 70 3a 1e 42 fe d9 c0 5d c0 0x0050 eb cd ee 07 b9 bf 82 1c 01 41 bb 15 36 0b 74 3a 0x0060 4b c8 74 9e 45 d7 5b 26 63 f4 24 e9 da ea 5c c6 0x0070 e8 59 d7 93 41 f7 94 df b7 ac 4d b7 ef c2 cc 4f 0x0080 5d 5f 66 d1 e5 e3 3f 2b ac 42 7c 5e 3a f1 9f 95 0x0090 d7 d9 e8 e9 3d 75 62 de 9b 05 86 e6 0e bf 79 4c 0x00A0 1d 0b 3a 76 9a 97 31 ba 12 74 ed 75 26 63 fe 79 0x00B0 17 5f bc 87 fd 58 9b 6f dd 0b 12 f2 65 2f 12 fb 0x00C0 1e 99 5e 37 b2 4c 42 4c 4f 4c af 1b 6c c4 be c7 0x00D0 c9 9f c0

Processing starts from the fist byte of SRC and suspends on 44th byte. Here is the intermediate result of that processing stored in 2048 byte buffer located right after the SRC buffer (actually, there are 10 bytes between them, where among other things an address of 44th byte is stored): 0x0200 00 80 01 00 5c ea 3f 01 00 00 0x020A 02 00 02 00 0e 00 04 00 1f 00 05 00 04 00 04 00 0x021A 18 00 05 00 3a 00 07 00 0d 00 05 00 00 00 00 00 0x022A 05 00 04 00 df 00 08 00 0d 00 08 00 de 00 08 00 0x023A 05 00 07 00 00 00 00 00 00 00 00 00 00 00 00 00 0x024A 00 00 05 00 05 00 05 00 00 00 00 00 00 00 00 00 0x025A 00 00 00 00 00 00 00 00 0c 00 08 00 00 00 00 00 0x026A 00 00 00 00 0f 00 08 00 0e 00 08 00 00 00 00 00 ... ZEROES ... 0x02CA 1a 00 05 00 00 00 00 00 00 00 00 00 0c 00 05 00 0x02DA 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x02EA 04 00 05 00 00 00 00 00 00 00 00 00 00 00 00 00 ... ZEROES ... 0x038A 6e 00 07 00 1c 00 06 00 00 00 00 00 00 00 00 00 0x039A 00 00 00 00 00 00 00 00 09 00 08 00 00 00 00 00 ... ZEROES ... 0x040A 19 00 05 00 00 00 00 00 00 00 00 00 07 00 05 00 0x041A 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x042A 06 00 05 00 00 00 00 00 00 00 00 00 00 00 00 00 ... ZEROES ... 0x05EA 00 00 00 00 3b 00 07 00 00 00 00 00 08 00 08 00 0x05FA 36 00 06 00 0f 00 05 00 1e 00 05 00 01 00 04 00 0x060A 05 10 00 00 05 10 00 00 05 10 00 00 05 10 00 00 0x061A 05 10 00 00 05 10 00 00 05 10 00 00 05 10 00 00 0x062A 08 fb 00 00 08 66 00 00 07 0c 00 00 07 0c 00 00 0x063A 08 16 00 00 08 0a 00 00 08 1a 00 00 08 19 00 00 0x064A 04 ff 00 00 04 ff 00 00 04 ff 00 00 04 ff 00 00 0x065A 04 ff 00 00 04 ff 00 00 04 ff 00 00 04 ff 00 00 0x066A 04 ff 00 00 04 ff 00 00 04 ff 00 00 04 ff 00 00 0x067A 04 ff 00 00 04 ff 00 00 04 ff 00 00 04 ff 00 00 0x068A 05 38 00 00 05 38 00 00 05 38 00 00 05 38 00 00 0x069A 05 38 00 00 05 38 00 00 05 38 00 00 05 38 00 00 0x06AA 05 11 00 00 05 11 00 00 05 11 00 00 05 11 00 00 0x06BA 05 11 00 00 05 11 00 00 05 11 00 00 05 11 00 00 0x06CA 05 88 00 00 05 88 00 00 05 88 00 00 05 88 00 00 0x06DA 05 88 00 00 05 88 00 00 05 88 00 00 05 88 00 00 0x06EA 05 83 00 00 05 83 00 00 05 83 00 00 05 83 00 00 0x06FA 05 83 00 00 05 83 00 00 05 83 00 00 05 83 00 00 0x070A 04 03 00 00 04 03 00 00 04 03 00 00 04 03 00 00 0x071A 04 03 00 00 04 03 00 00 04 03 00 00 04 03 00 00 0x072A 04 03 00 00 04 03 00 00 04 03 00 00 04 03 00 00 0x073A 04 03 00 00 04 03 00 00 04 03 00 00 04 03 00 00 0x074A 04 08 00 00 04 08 00 00 04 08 00 00 04 08 00 00 0x075A 04 08 00 00 04 08 00 00 04 08 00 00 04 08 00 00 0x076A 04 08 00 00 04 08 00 00 04 08 00 00 04 08 00 00 0x077A 04 08 00 00 04 08 00 00 04 08 00 00 04 08 00 00 0x078A 05 33 00 00 05 33 00 00 05 33 00 00 05 33 00 00 0x079A 05 33 00 00 05 33 00 00 05 33 00 00 05 33 00 00 0x07AA 05 06 00 00 05 06 00 00 05 06 00 00 05 06 00 00 0x07BA 05 06 00 00 05 06 00 00 05 06 00 00 05 06 00 00 0x07CA 06 61 00 00 06 61 00 00 06 61 00 00 06 61 00 00 0x07DA 07 05 00 00 07 05 00 00 07 f9 00 00 07 f9 00 00 0x07EA 05 fd 00 00 05 fd 00 00 05 fd 00 00 05 fd 00 00 0x07FA 05 fd 00 00 05 fd 00 00 05 fd 00 00 05 fd 00 00 0x080A 02 00 00 00 02 00 00 00 02 00 00 00 02 00 00 00 0x081A 02 00 00 00 02 00 00 00 02 00 00 00 02 00 00 00 0x082A 02 00 00 00 02 00 00 00 02 00 00 00 02 00 00 00 0x083A 02 00 00 00 02 00 00 00 02 00 00 00 02 00 00 00 0x084A 02 00 00 00 02 00 00 00 02 00 00 00 02 00 00 00 0x085A 02 00 00 00 02 00 00 00 02 00 00 00 02 00 00 00 0x086A 02 00 00 00 02 00 00 00 02 00 00 00 02 00 00 00 0x087A 02 00 00 00 02 00 00 00 02 00 00 00 02 00 00 00 0x088A 02 00 00 00 02 00 00 00 02 00 00 00 02 00 00 00 0x089A 02 00 00 00 02 00 00 00 02 00 00 00 02 00 00 00 0x08AA 02 00 00 00 02 00 00 00 02 00 00 00 02 00 00 00 0x08BA 02 00 00 00 02 00 00 00 02 00 00 00 02 00 00 00 0x08CA 02 00 00 00 02 00 00 00 02 00 00 00 02 00 00 00 0x08DA 02 00 00 00 02 00 00 00 02 00 00 00 02 00 00 00 0x08EA 02 00 00 00 02 00 00 00 02 00 00 00 02 00 00 00 0x08FA 02 00 00 00 02 00 00 00 02 00 00 00 02 00 00 00 0x090A 05 04 00 00 05 04 00 00 05 04 00 00 05 04 00 00 0x091A 05 04 00 00 05 04 00 00 05 04 00 00 05 04 00 00 0x092A 05 80 00 00 05 80 00 00 05 80 00 00 05 80 00 00 0x093A 05 80 00 00 05 80 00 00 05 80 00 00 05 80 00 00 0x094A 05 30 00 00 05 30 00 00 05 30 00 00 05 30 00 00 0x095A 05 30 00 00 05 30 00 00 05 30 00 00 05 30 00 00 0x096A 06 fc 00 00 06 fc 00 00 06 fc 00 00 06 fc 00 00 0x097A 07 60 00 00 07 60 00 00 08 0b 00 00 08 09 00 00 0x098A 04 01 00 00 04 01 00 00 04 01 00 00 04 01 00 00 0x099A 04 01 00 00 04 01 00 00 04 01 00 00 04 01 00 00 0x09AA 04 01 00 00 04 01 00 00 04 01 00 00 04 01 00 00 0x09BA 04 01 00 00 04 01 00 00 04 01 00 00 04 01 00 00 0x09CA 05 fe 00 00 05 fe 00 00 05 fe 00 00 05 fe 00 00 0x09DA 05 fe 00 00 05 fe 00 00 05 fe 00 00 05 fe 00 00 0x09EA 05 02 00 00 05 02 00 00 05 02 00 00 05 02 00 00 0x09FA 05 02 00 00 05 02 00 00 05 02 00 00 05 02 00 00

Processing continues from 44th byte of SRC. The remaining bytes are processed with result stored in external intemediate buffer: IMM: Intermediate data, 323 bytes: 0x0000 00 00 00 00 08 00 0a 00 ff 06 05 66 fe 00 61 05 0x0010 11 ff 60 04 00 fc 11 00 16 61 01 11 ff 01 01 11 0x0020 01 00 fe 06 60 02 11 01 00 fc 10 00 06 11 02 00 0x0030 fe 01 10 01 00 ff 01 03 11 02 00 fc 61 10 00 01 0x0040 01 10 01 00 fe 06 01 01 10 fe 01 06 02 00 fb 61 0x0050 10 11 10 60 04 00 00 00 06 00 0c 00 01 00 ff 30 0x0060 03 00 fe 03 83 03 00 fd 38 08 30 01 00 fc 03 80 0x0070 00 83 01 00 ff 38 01 00 f9 08 30 00 08 80 00 88 0x0080 01 00 ff 33 01 00 fe 03 30 19 00 fe 08 88 02 00 0x0090 0b 00 04 00 06 00 09 00 02 00 ff 33 04 00 fd 08 0x00A0 30 00 02 33 fc 00 83 00 08 01 88 fd 80 08 30 04 0x00B0 00 ff 83 04 00 fe 83 08 01 88 fd 80 08 30 02 33 0x00C0 fe 00 83 03 00 fd 08 30 00 04 00 0b 00 06 00 0c 0x00D0 00 ff 00 01 33 ff 30 02 00 fe 08 88 1a 00 ff 33 0x00E0 01 00 f9 03 30 00 08 80 00 88 01 00 ff 38 01 00 0x00F0 f9 08 30 00 03 80 00 83 02 00 fd 38 08 30 02 00 0x0100 fe 03 83 02 00 00 00 04 00 06 00 09 00 01 00 ff 0x0110 33 03 00 fe 03 80 03 00 fe 38 00 02 33 fd 03 80 0x0120 08 01 88 fe 80 38 04 00 ff 38 04 00 fd 03 80 08 0x0130 01 88 fc 80 00 38 00 02 33 fd 00 03 80 02 00 00 0x0140 00 00 00

Finally, some processing performed on IMM and we have the result: DST: The Result, 372 bytes: 0x0000 00 00 00 00 08 00 0A 00 06 66 66 66 66 66 66 00 0x0010 67 77 77 77 77 77 77 60 67 77 77 77 77 66 77 76 0x0020 06 66 66 76 66 77 77 76 00 06 77 67 77 77 77 66 0x0030 00 00 66 67 77 77 76 76 00 00 67 76 66 66 67 76 0x0040 00 00 06 66 66 67 77 66 00 00 00 67 76 77 76 60 0x0050 00 00 00 06 66 66 66 00 04 00 00 00 06 00 0C 00 0x0060 00 00 30 00 00 00 00 03 B3 00 00 00 00 3B BB 30 0x0070 00 00 03 BB BB B3 00 00 3B BB BB BB 30 00 33 3B 0x0080 BB 33 30 00 00 3B BB 30 00 00 00 3B BB 30 00 00 0x0090 00 3B BB 30 00 00 00 3B BB 30 00 00 00 3B BB 30 0x00A0 00 00 00 33 33 30 00 00 0B 00 04 00 06 00 09 00 0x00B0 00 00 00 33 00 00 00 00 00 3B 30 00 33 33 33 3B 0x00C0 B3 00 3B BB BB BB BB 30 3B BB BB BB BB B3 3B BB 0x00D0 BB BB BB 30 33 33 33 3B B3 00 00 00 00 3B 30 00 0x00E0 00 00 00 33 00 00 04 00 0B 00 06 00 0C 00 00 33 0x00F0 33 30 00 00 00 3B BB 30 00 00 00 3B BB 30 00 00 0x0100 00 3B BB 30 00 00 00 3B BB 30 00 00 00 3B BB 30 0x0110 00 00 33 3B BB 33 30 00 3B BB BB BB 30 00 03 BB 0x0120 BB B3 00 00 00 3B BB 30 00 00 00 03 B3 00 00 00 0x0130 00 00 30 00 00 00 00 00 04 00 06 00 09 00 00 00 0x0140 33 00 00 00 00 03 B3 00 00 00 00 3B B3 33 33 33 0x0150 03 BB BB BB BB B3 3B BB BB BB BB B3 03 BB BB BB 0x0160 BB B3 00 3B B3 33 33 33 00 03 B3 00 00 00 00 00 0x0170 33 00 00 00

Decompression completed and it's easy to derive bitmaps like this: Get first 8 bytes of DST : 00 00 00 00 08 00 0A 00 Multiply last 2 words : 08 * 0A = 50 (80) Get next 80 bytes of DST : 06 66 66 66 66 66 66 00 67 77 77 77 77 77 77 60 67 77 77 77 77 66 77 76 06 66 66 76 66 77 77 76 00 06 77 67 77 77 77 66 00 00 66 67 77 77 76 76 00 00 67 76 66 66 67 76 00 00 06 66 66 67 77 66 00 00 00 67 76 77 76 60 00 00 00 06 66 66 66 00 Arrange those bytes assuming that 08 and 0A are width and height respectively: 06 66 66 66 66 66 66 00 67 77 77 77 77 77 77 60 67 77 77 77 77 66 77 76 06 66 66 76 66 77 77 76 00 06 77 67 77 77 77 66 00 00 66 67 77 77 76 76 00 00 67 76 66 66 67 76 00 00 06 66 66 67 77 66 00 00 00 67 76 77 76 60 00 00 00 06 66 66 66 00 Extend this with zeroes: 00 06 06 06 06 06 06 06 06 06 06 06 06 06 00 00 06 07 07 07 07 07 07 07 07 07 07 07 07 07 06 00 06 07 07 07 07 07 07 07 07 07 06 06 07 07 07 06 00 06 06 06 06 06 07 06 06 06 07 07 07 07 07 06 00 00 00 06 07 07 06 07 07 07 07 07 07 07 06 06 00 00 00 00 06 06 06 07 07 07 07 07 07 06 07 06 00 00 00 00 06 07 07 06 06 06 06 06 06 07 07 06 00 00 00 00 00 06 06 06 06 06 06 07 07 07 06 06 00 00 00 00 00 00 06 07 07 06 07 07 07 06 06 00 00 00 00 00 00 00 00 06 06 06 06 06 06 06 00 00 Thats it! Wrapping it in BMP header gives us a cute cursor image: .

And here are the others: .