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| # SPDX-License-Identifier: MIT | |
| import sys | |
| def decompress_osdsys(src, dst): | |
| run = 0 | |
| src_offset = 0 | |
| dst_offset = 0 | |
| state_length = 0 | |
| state_block_desc = 0 | |
| state_n = 0 | |
| state_shift = 0 | |
| state_mask = 0 | |
| state_length = int.from_bytes(src[src_offset:src_offset + 4], byteorder="little") | |
| src_offset += 4 | |
| def safe_read(src, src_offset): | |
| if src_offset >= len(src) or src_offset < 0: | |
| return 0 | |
| return src[src_offset] | |
| def safe_write(dst, dst_offset, val): | |
| if dst_offset >= len(dst) or dst_offset < 0: | |
| return | |
| dst[dst_offset] = val | |
| while dst_offset <= state_length: | |
| if run == 0: | |
| run = 30 | |
| state_block_desc = 0 | |
| for i in range(4): | |
| state_block_desc <<= 8 | |
| state_block_desc |= safe_read(src, src_offset) | |
| src_offset += 1 | |
| state_n = state_block_desc & 3 | |
| state_shift = 14 - state_n | |
| state_mask = 0x3FFF >> state_n | |
| if (state_block_desc & (1 << (run + 1))) == 0: | |
| safe_write(dst, dst_offset, safe_read(src, src_offset)) | |
| dst_offset += 1 | |
| src_offset += 1 | |
| else: | |
| h = safe_read(src, src_offset) << 8 | |
| src_offset += 1 | |
| h |= safe_read(src, src_offset) | |
| src_offset += 1 | |
| copy_offset = dst_offset - ((h & state_mask) + 1) | |
| m = 2 + (h >> state_shift) | |
| for i in range(m + 1): | |
| safe_write(dst, dst_offset, safe_read(dst, copy_offset)) | |
| dst_offset += 1 | |
| copy_offset += 1 | |
| run -= 1 | |
| if __name__ == "__main__": | |
| indata = b"" | |
| with open(sys.argv[1], "rb") as f: | |
| indata = f.read() | |
| outdata_len = int.from_bytes(indata[0:4], byteorder="little") | |
| if outdata_len > len(indata) * 16: | |
| print(outdata_len) | |
| raise Exception("Invalid output length") | |
| outdata = bytearray(outdata_len) | |
| decompress_osdsys(indata, outdata) | |
| with open(sys.argv[2], "wb") as wf: | |
| wf.write(outdata) |
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