no op (no operation)
What is no op (no operation)?
No op means no operation, which is a computer instruction that specifies no operation but takes up a small amount of storage space. When the computer processor encounters a no op instruction, it simply moves to the next sequential instruction.
A no op instruction simply tells a program to do nothing if a conditional statement is satisfied. It doesn't change the status of any registers, status flags or memory that are accessible to a programmer. If it did affect those elements, it could lead to a memory or page fault. Thus when a function or set of statements in code have no effect or intended purpose, the result is a no op. That's why no op is sometimes known as a "do-nothing" instruction. No op may also be spelled as no-op, noop or NOP.
The New Hacker's Dictionary also includes a derivative meaning of the term no op as "a person who contributes nothing to a project, or has nothing going on upstairs, or both. As in 'He's a no-op.'"
Uses of no operation
No op acts as a blank instruction or placeholder in code for timing purposes and for inserting useful instructions later during development. It allows the processor to move to the next consecutive instruction. It also serves to delay CPU activity and may work with other instructions to facilitate a particular result.
The instruction may also be used to do the following:
- Force memory alignment.
- Void an existing instruction,
- Occupy a branch delay slot.
- Prevent hazards in the CPU's instruction pipeline that may lead to incorrect results.
No op in assembler languages
An assembler language is machine code, a type of low-level programming language that directly communicates with computer hardware and is close to machine language, albeit with simpler language and code. Assembly language code can be created either using an assembler, which is a compiler of assembly language, or by a human programmer.
The no op instruction is included in most assembler languages and may have a label. In these languages, one of its main purposes is to help align instruction addresses and improve processor performance. With a no op, programmers can ensure the alignment of the sequence of memory blocks to be read is always maintained.
Such alignment lets the processor access required data from memory. It also doesn't need to continually fetch the last blocks of the previous block, which increases processor speed and performance.
No op may be used to crack and pirate software
Most of the time, no ops are used for legitimate purposes, such as to align instruction addresses, improve processor performance and add a placeholder in code (e.g., when callbacks are not given).
However, no ops can also be used for unethical purposes. One example is to crack software. Software pirates use no op to exploit a software's licensing protection features.
They do this by replacing conditional jumps within the functions of license check routines with no ops. The routine still completes; however, the condition to check for the license and return a particular expected value is circumvented. This fools the software into bypassing the protection checks so its unlicensed (i.e., pirated or stolen) versions can be used.
No operation syntax
The no op instruction consists of an operation code (0000) but no operands, allowing separation between instructions with adjacent instruction addresses and gaps in the instruction stream. No op may not be branched. However, it may precede or follow any machine instruction. The only exception is the end instruction. An unlimited number of no op instructions may be successfully used in the instruction stream. No authorization is required and there are no exceptions.
The actual syntax of no op depends on the language. For example, in ADA -- an imperative, high-level OOP language -- no op is the null statement. The null statement is also no op in C. This statement may be written simply as a semicolon or as an empty {} block statement. JavaScript does not have a built-in no op statement, so alternates like a empty semicolon statement, empty {} block statement, or the undefined or null expression may be used.
Other languages do include built-in no op instructions:
- JQuery. Function: jQuery.noop().
- AngularJS. Function: angular.noop
- Lodash. Function: .noop().
- Pascal. ; or block with BEGIN END
- Python. Statement: pass.
- TeX. Command: \relax.
Noop language experiment at Google
The machine instruction no op should not be confused with Noop (pronounced noh-awp). Noop started as a language experiment at Google in 2009. Its primary aim was to encourage good coding practices by promoting the best lessons learned from the languages that had emerged over the previous 20 years.
The goals of the developers of Noop included the following:
- Build dependency injection and testability into the language from the beginning.
- Optimize code testability, modification ease and readability.
- Encourage developers to avoid the misuse of subclasses and APIs as well as obligatory and redundant boilerplates.
- Encourage developers to avoid primitive types and implementation inheritance.
- Encourage immutability and minimal variable scope by ensuring easy access to a functional style.
- Maintain updated and executable documentation at all times.
As a new language, Noop was initially planned to run on the Java virtual machine. Its source form was similar to Java. Noop source files could be used in one of three ways:
- With a Java translator that produces Java code and requires no codebase conversion.
- Through an interpreter that reads and evaluates the code and includes a command-line interface.
- By compiling to Java bytecode.
Learn more about Java and why it was designed to be platform independent.