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hi all,
i am downloading a program to a hardware device having limited memory.
is it possible to compress different parts of the program in the device and decompress it when it is to be used?
which algorithm shall i use?
thanx in advance
ratheeshravi
To do this, you need to be able to separate your code into chunks that have as little coupling as possible between them. You must then be able to have an encryption/decryption engine that operates on the chunks fit in the memory and develop the rules for encryption/decryption of chunks prior to calls from one chunk to another. This is difficult in standard c++ because the language does not have a notion of the size of functions, but is possible if the c++ works directly on the machine language memory area of the code using unsafe casts and builds function pointers. However, this is only a reasonable approach if the size of the encryption/decryption engine + a decompression buffer do not make the excutable larger than the compressed version.
The proper compression algorithm depends on the instruction set of the processor you are targetting. If it is a small, fixed (N) bit instruction set, then an N-bit huffman compression could be proper (or at least compression on the operand bit size if the data bit size is a multiple).
Also note that such techniques decrease the performance of the program, which is often not acceptable for embedded devices.
If you are using WinCE or something similar, you can write most of your code in a .dll and decompress it before you dynamically load it. It is fairly simple to do.