Bytecode

Bytecode, also termed portable code or p-code, is a form of designed for efficient execution by a software. Unlike, bytecodes are compact numeric codes, constants, and references (normally numeric addresses) that encode the result of  parsing and performing  of things like type, scope, and nesting depths of program objects.

The name bytecode stems from instruction sets that have one- s followed by optional parameters. s such as bytecode may be output by implementations to ease, or it may be used to reduce hardware and  dependence by allowing the same code to run , on different devices. Bytecode may often be either directly executed on a (a  i.e., interpreter), or it may be further compiled into  for better performance.

Since bytecode instructions are processed by software, they may be arbitrarily complex, but are nonetheless often akin to traditional hardware instructions: virtual s are the most common, but virtual s have been built also. Different parts may often be stored in separate files, similar to, but dynamically loaded during execution.

Execution
A bytecode program may be executed by parsing and directly executing the instructions, one at a time. This kind of bytecode interpreter is very portable. Some systems, called dynamic translators, or  (JIT) compilers, translate bytecode into as necessary at. This makes the virtual machine hardware-specific but doesn't lose the portability of the bytecode. For example, and  code is typically stored in bytecode format, which is typically then JIT compiled to translate the bytecode to machine code before execution. This introduces a delay before a program is run, when the bytecode is compiled to native machine code, but improves execution speed considerably compared to interpreting source code directly, normally by around an order of magnitude (10x).

Because of its performance advantage, today many language implementations execute a program in two phases, first compiling the source code into bytecode, and then passing the bytecode to the virtual machine. There are bytecode based virtual machines of this sort for, , , , ,  and  (however, Forth is seldom compiled via bytecodes in this way, and its virtual machine is more generic instead). The implementation of and  1.8 instead work by walking an  representation derived from the source code.

More recently, the authors of and  have challenged the notion that intermediate bytecode is needed for fast and efficient VM implementation. Both of these language implementations currently do direct JIT compiling from source code to machine code with no bytecode intermediary.

Examples

 * executes in the ActionScript Virtual Machine (AVM), which is part of Flash Player and AIR. ActionScript code is typically transformed into bytecode format by a . Examples of compilers include one built into Adobe Flash Professional and one built into Adobe Flash Builder and available in the Adobe Flex SDK.
 * objects
 * , originally bytecode for an interface-building tool but used also as a language
 * C to compilers
 * implementation of used to compile only to bytecode for many years; however, now it also supports compiling to native code with the help of
 * and Scieneer Common Lisp implementations of can compile either to native code or to bytecode, which is far more compact
 * executed by, used by languages such as
 * Dalvik bytecode, designed for the platform, is executed by the
 * Dis bytecode, designed for the, is executed by the
 * for the programming language
 * EM, the virtual machine used as an intermediate compiling language and as a modern bytecode language
 * is a text editor with most of its functions implemented by, its built-in dialect of . These features are compiled into bytecode. This architecture allows users to customize the editor with a high level language, which after compiling into bytecode yields reasonable performance.
 * implementation of can compile to bytecode or C code
 * Ericsson implementation of uses BEAM bytecodes
 * and programming languages
 * used the to make its software applications more portable
 * , which is executed by the
 * , the keyboard driver with its resource file  containing layout information and short  sequences executed by an interpreter inside the resident driver.
 * , a modular bytecode compiler and virtual machine
 * LSL, a scripting language used in virtual worlds compiles in bytecode running on a virtual machine. Second Life has the original Mono version, Inworldz developed the Phlox version.
 * language uses a register-based bytecode virtual machine
 * m-code of the language
 * of the programming language
 * language optionally compiles to a compact bytecode form
 * of implementation of the  language
 * also referred to as Data BASIC or
 * The offers a bytecode compiler through the compiler package, now standard with R version 2.13.0. It is possible to compile this version of R so that the base and recommended packages exploit this.
 * implementation of Scheme using bytecode interpreter
 * Bytecodes of many implementations of the language
 * The built into the  Propeller
 * The database engine translates SQL statements into a bespoke byte-code format.
 * compiles to bytecode
 * and for
 * also referred to as Data BASIC or
 * The offers a bytecode compiler through the compiler package, now standard with R version 2.13.0. It is possible to compile this version of R so that the base and recommended packages exploit this.
 * implementation of Scheme using bytecode interpreter
 * Bytecodes of many implementations of the language
 * The built into the  Propeller
 * The database engine translates SQL statements into a bespoke byte-code format.
 * compiles to bytecode
 * and for
 * compiles to bytecode
 * and for
 * and for