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Extending The C Programming Language to Handle Multi-Formatted N-Bit Blocks

Extending The C Programming Language to Handle Multi-Formatted N-Bit Blocks. Jing Yang Department of Computer Science University of Virginia. Multi-Formatted N-Bit Blocks. Applications in a variety of domains need to represent and manipulate blocks of data at the bit level

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Extending The C Programming Language to Handle Multi-Formatted N-Bit Blocks

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  1. Extending The C Programming Language to Handle Multi-Formatted N-Bit Blocks Jing Yang Department of Computer Science University of Virginia

  2. Multi-Formatted N-Bit Blocks • Applications in a variety of domains need to represent and manipulate blocks of data at the bit level • Binary analysis – instruction encoding & decoding • Computer networks – packet classification (filtering) • Cryptography – the Rijndael algorithm (AES)

  3. The SPARC ISA

  4. IPv4 Packet Header

  5. AES – Substitution

  6. AES – Row Shifting

  7. AES – Column Mixing

  8. Characteristics • Continuously allocated in the memory • Variable-sized with an upper limit (a multiple of 8 bits) • Partitioned into several fields, each taking up a few bits (not necessarily continuous) – a format • Have multiple formats and the exact format of an instance may change during runtime – due to context or algorithm

  9. Languages • C • Aggregate types • Bit shifting & masking • ML • Strong type system • C++ or Java • Class • Domain-specific languages

  10. An Example

  11. Type Bob

  12. Type Interpret

  13. A Small C-Like Language with Extensions

  14. Typing Rules

  15. Derivation Rules for The Type System

  16. Type Safety

  17. Simplex Type Checking • Static type checking • Dynamic type checking • Track the type during runtime • High overhead

  18. Hybrid Type Checking – Static Analysis • The strict type system • The relaxed type system

  19. Hybrid Type Checking – Dynamic Analysis

  20. Hybrid Type Checking – Dynamic Analysis

  21. Implementation • Build upon CIL • Bob -> array of unsigned char • Bob ref -> unsigned char ref • Interpret -> no visible code • Bob field access -> a sequence of bit shifting & masking • Optimization – several accesses combined to one single word implementation

  22. Evaluation • Can only run trivial programs now, but • The revised code still shows: • Clearer structure • Shorter size • At least the same performance

  23. Questions ?

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