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ProGuard
ProGuard is an open source command-line tool which shrinks, optimizes and obfuscates Java code. It is able to optimize bytecode as well as detect and remove unused instructions. ProGuard is free software and is distributed under the GNU General Public License, version 2. ProGuard was distributed as part of the Android SDK and ran when building the application in release mode. Features * Bytecode-level optimizations; * Also works with Java Micro Edition and Android; Obfuscation Method ProGuard obfuscates Java and Android programs by renaming classes, fields, and methods using meaningless names (an implementation of security through obscurity), making it more difficult to reverse-engineer the final application. Optimization Besides removing unused instructions from the compiled bytecode, ProGuard optimizes it using techniques such as control flow analysis, data-flow analysis, partial evaluation, static single assignment, global value numbering, and liveness an ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Obfuscation (software)
In software development, obfuscation is the practice of creating source code, source or machine code that is intentionally difficult for humans or computers to understand. Similar to obfuscation in natural language, code obfuscation may involve using unnecessarily roundabout ways to write statements. Programmers often obfuscate code to conceal its purpose, logic, or embedded values. The primary reasons for doing so are to prevent Anti-tamper software, tampering, deter reverse engineering, or to create a puzzle or recreational challenge to deobfuscate the code, a challenge often included in Crackme, crackmes. While obfuscation can be done manually, it is more commonly performed using Executable compression, obfuscators. Overview The architecture and characteristics of some languages may make them easier to obfuscate than others. C (programming language), C, C++, and the Perl programming language are some examples of languages easy to obfuscate. Haskell (programming language), Hask ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Java (programming Language)
Java is a High-level programming language, high-level, General-purpose programming language, general-purpose, Memory safety, memory-safe, object-oriented programming, object-oriented programming language. It is intended to let programmers ''write once, run anywhere'' (Write once, run anywhere, WORA), meaning that compiler, compiled Java code can run on all platforms that support Java without the need to recompile. Java applications are typically compiled to Java bytecode, bytecode that can run on any Java virtual machine (JVM) regardless of the underlying computer architecture. The syntax (programming languages), syntax of Java is similar to C (programming language), C and C++, but has fewer low-level programming language, low-level facilities than either of them. The Java runtime provides dynamic capabilities (such as Reflective programming, reflection and runtime code modification) that are typically not available in traditional compiled languages. Java gained popularity sh ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Method (computer Programming)
A method in object-oriented programming (OOP) is a procedure associated with an object, and generally also a message. An object consists of ''state data'' and ''behavior''; these compose an ''interface'', which specifies how the object may be used. A method is a behavior of an object parametrized by a user. Data is represented as properties of the object, and behaviors are represented as methods. For example, a Window object could have methods such as open and close, while its state (whether it is open or closed at any given point in time) would be a property. In class-based programming, methods are defined within a class, and objects are instances of a given class. One of the most important capabilities that a method provides is '' method overriding'' - the same name (e.g., area) can be used for multiple different kinds of classes. This allows the sending objects to invoke behaviors and to delegate the implementation of those behaviors to the receiving object. A method in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Debugging
In engineering, debugging is the process of finding the Root cause analysis, root cause, workarounds, and possible fixes for bug (engineering), bugs. For software, debugging tactics can involve interactive debugging, control flow analysis, Logfile, log file analysis, monitoring at the application monitoring, application or system monitoring, system level, memory dumps, and profiling (computer programming), profiling. Many Programming language, programming languages and Programming tool, software development tools also offer programs to aid in debugging, known as debuggers. Etymology The term ''bug'', in the sense of defect, dates back at least to 1878 when Thomas Edison wrote "little faults and difficulties" in his inventions as "Bugs". A popular story from the 1940s is from Admiral Grace Hopper. While she was working on a Harvard Mark II, Mark II computer at Harvard University, her associates discovered a moth stuck in a relay that impeded operation and wrote in a log book ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tail Recursion
In computer science, a tail call is a subroutine call performed as the final action of a procedure. If the target of a tail is the same subroutine, the subroutine is said to be tail recursive, which is a special case of direct recursion. Tail recursion (or tail-end recursion) is particularly useful, and is often easy to optimize in implementations. Tail calls can be implemented without adding a new stack frame to the call stack. Most of the frame of the current procedure is no longer needed, and can be replaced by the frame of the tail call, modified as appropriate (similar to overlay for processes, but for function calls). The program can then jump to the called subroutine. Producing such code instead of a standard call sequence is called tail-call elimination or tail-call optimization. Tail-call elimination allows procedure calls in tail position to be implemented as efficiently as goto statements, thus allowing efficient structured programming. In the words of Guy L. Steele, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Inline Expansion
In computing, inline expansion, or inlining, is a manual or compiler optimization that replaces a function call site with the body of the called function. Inline expansion is similar to macro expansion, but occurs during compiling, without changing the source code (the text), while macro expansion occurs before compiling, and results in different text that is then processed by the compiler. Inlining is an important optimization, but has complex effects on performance. As a rule of thumb, some inlining will improve speed at very minor cost of space, but excess inlining will hurt speed, due to inlined code consuming too much of the instruction cache, and also cost significant space. A survey of the modest academic literature on inlining from the 1980s and 1990s is given in Peyton Jones & Marlow 1999. Overview Inline expansion is similar to macro expansion as the compiler places a new copy of the function in each place it is called. Inlined functions run a little faster than the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Memory Management
Memory management (also dynamic memory management, dynamic storage allocation, or dynamic memory allocation) is a form of Resource management (computing), resource management applied to computer memory. The essential requirement of memory management is to provide ways to dynamically allocate portions of memory to programs at their request, and free it for reuse when no longer needed. This is critical to any advanced computer system where more than a single Process (computing), process might be underway at any time. Several methods have been devised that increase the effectiveness of memory management. Virtual memory systems separate the memory addresses used by a process from actual physical addresses, allowing separation of processes and increasing the size of the virtual address space beyond the available amount of Random-access memory, RAM using paging or swapping to secondary storage. The quality of the virtual memory manager can have an extensive effect on overall system C ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Peephole Optimizations
Peephole optimization is an optimization technique performed on a small set of compiler-generated instructions, known as a peephole or window, that involves replacing the instructions with a logically equivalent set that has better performance. For example: * Instead of pushing a register onto the stack and then immediately popping the value back into the register, remove both instructions * Instead of multiplying ''x'' by 2, do * Instead of multiplying a floating point register by 8, add 3 to the floating point register's exponent The term ''peephole optimization'' was introduced by William Marshall McKeeman in 1965. Replacements Peephole optimization replacements include but are not limited to: * Null sequences – Delete useless operations * Combine operations – Replace several operations with one equivalent * Algebraic laws – Use algebraic laws to simplify or reorder instructions * Special case instructions – Use instructions designed for special operand cases * Addr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Live Variable Analysis
In compilers, live variable analysis (or simply liveness analysis) is a classic data-flow analysis to calculate the variables that are ''live'' at each point in the program. A variable is ''live'' at some point if it holds a value that may be needed in the future, or equivalently if its value may be read before the next time the variable is written to. Example Consider the following program: b = 3 c = 5 a = f(b * c) The set of live variables between lines 2 and 3 is because both are used in the multiplication on line 3. But the set of live variables after line 1 is only , since variable c is updated later, on line 2. The value of variable a is not used in this code. Note that the assignment to a may be eliminated as a is not used later, but there is insufficient information to justify removing all of line 3 as f may have side effects (printing b * c, perhaps). Expression in terms of dataflow equations Liveness analysis is a "backwards may" analysis. The analysis is done ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Global Value Numbering
Value numbering is a technique of determining when two computations in a program are equivalent and eliminating one of them with a semantics-preserving optimization. Global value numbering Global value numbering (GVN) is a compiler optimization based on the static single assignment form (SSA) intermediate representation. It sometimes helps eliminate redundant code that common subexpression elimination (CSE) does not. At the same time, however, CSE may eliminate code that GVN does not, so both are often found in modern compilers. Global value numbering is distinct from local value numbering in that the value-number mappings hold across basic block boundaries as well, and different algorithms are used to compute the mappings. Global value numbering works by assigning a value number to variables and expressions. The same value number is assigned to those variables and expressions which are equivalent. For instance, in the following code: w := 3 x := 3 y := x + 4 z := w + 4 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Static Single Assignment Form
In compiler design, static single assignment form (often abbreviated as SSA form or simply SSA) is a type of intermediate representation (IR) where each variable is assigned exactly once. SSA is used in most high-quality optimizing compilers for imperative languages, including LLVM, the GNU Compiler Collection, and many commercial compilers. There are efficient algorithms for converting programs into SSA form. To convert to SSA, existing variables in the original IR are split into versions, new variables typically indicated by the original name with a subscript, so that every definition gets its own version. Additional statements that assign to new versions of variables may also need to be introduced at the join point of two control flow paths. Converting from SSA form to machine code is also efficient. SSA makes numerous analyses needed for optimizations easier to perform, such as determining use-define chains, because when looking at a use of a variable there is only one place ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Partial Evaluation
In computing, partial evaluation is a technique for several different types of program optimization by specialization. The most straightforward application is to produce new programs that run faster than the originals while being guaranteed to behave in the same way. A computer program ''prog'' is seen as a mapping of input data into output data: prog : I_\text \times I_\text \to O, where I_\text, the ''static data'', is the part of the input data known at compile time. The partial evaluator transforms \langle prog, I_\text\rangle into prog^* : I_\text \to O by precomputing all static input at compile time. prog^* is called the "residual program" and should run more efficiently than the original program. The act of partial evaluation is said to "residualize" prog to prog^*. Futamura projections A particularly interesting example of the use of partial evaluation, first described in the 1970s by Yoshihiko Futamura, is when ''prog'' is an interpreter for a programming language ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
