Machine code - Wikipedia
Machine language (also known as machine code) is the series of bit patterns that What is the difference between high level language, assembly language, .. It will show opcodes on the left, and the corresponding assembly** on the right. Assembly language provides much better readability of a machine code, as it is the difference between the memory addresses of two consecutive machine. machine code and its human-readable representation as assembly code. Understanding the relation between source code and the generated assembly can often be a exercises illustrating different aspects of assembly language and compilers. .. This is the object code corresponding to the assembly instructions listed.
ARM instructions can be bit, bits wide or bit wide, depending on which mode is being used. So there is a slightly higher level language called assembly language which is a text representation of the machine code. A program called an assembler is then used to convert from the assembly language to the machine code.
This means that to set the value of two variables and then add them together takes 8 lines of code. Imagine how much code you would need to write a game like Clash Royale! The equivalent program is C is just three lines long, quite a saving!
A slightly more human readable form of machine code is called assembly language and a program called an assembler is used to convert the assembly notations into machine code. Normally apps for Android are written in Java. This works well for the majority of apps, but if you need to squeeze that extra bit of performance out of your app then you might want to write the code in C or directly in assembly language. The C is then compiled directly to machine code.
Difference Between Machine Language and Assembly Language | Machine Language vs Assembly Language
Or if you want the ultimate level of control then you can even write assembly code using the NDK! Nerds only need apply. They run programs stored somewhere on the system and are flexible universal in the sense that it can run any computable algorithm.
Extended mnemonics are often used to support specialized uses of instructions, often for purposes not obvious from the instruction name. For example, many CPU's do not have an explicit NOP instruction, but do have instructions that can be used for the purpose.
In CPUs the instruction xchg ax,ax is used for nop, with nop being a pseudo-opcode to encode the instruction xchg ax,ax. Some disassemblers recognize this and will decode the xchg ax,ax instruction as nop. For instance, with some Z80 assemblers the instruction ld hl,bc is recognized to generate ld l,c followed by ld h,b.
- Difference Between Machine Language and Assembly Language
- Machine code
Mnemonics are arbitrary symbols; in the IEEE published Standard for a uniform set of mnemonics to be used by all assemblers. The standard has since been withdrawn. Data directives[ edit ] There are instructions used to define data elements to hold data and variables.
They define the type of data, the length and the alignment of data. These instructions can also define whether the data is available to outside programs programs assembled separately or only to the program in which the data section is defined. Some assemblers classify these as pseudo-ops. Assembly directives[ edit ] Assembly directives, also called pseudo-opcodes, pseudo-operations or pseudo-ops, are commands given to an assembler "directing it to perform operations other than assembling instructions.
Pseudo-ops can make the assembly of the program dependent on parameters input by a programmer, so that one program can be assembled different ways, perhaps for different applications. Or, a pseudo-op can be used to manipulate presentation of a program to make it easier to read and maintain.
Another common use of pseudo-ops is to reserve storage areas for run-time data and optionally initialize their contents to known values. Symbolic assemblers let programmers associate arbitrary names labels or symbols with memory locations and various constants.
Usually, every constant and variable is given a name so instructions can reference those locations by name, thus promoting self-documenting code.
In executable code, the name of each subroutine is associated with its entry point, so any calls to a subroutine can use its name. Inside subroutines, GOTO destinations are given labels. Some assemblers support local symbols which are lexically distinct from normal symbols e. Some assemblers, such as NASM, provide flexible symbol management, letting programmers manage different namespacesautomatically calculate offsets within data structuresand assign labels that refer to literal values or the result of simple computations performed by the assembler.
Labels can also be used to initialize constants and variables with relocatable addresses. Assembly languages, like most other computer languages, allow comments to be added to program source code that will be ignored during assembly.
Judicious commenting is essential in assembly language programs, as the meaning and purpose of a sequence of binary machine instructions can be difficult to determine.
The "raw" uncommented assembly language generated by compilers or disassemblers is quite difficult to read when changes must be made. Macros[ edit ] Many assemblers support predefined macros, and others support programmer-defined and repeatedly re-definable macros involving sequences of text lines in which variables and constants are embedded. The macro definition is most commonly [a] a mixture of assembler statements, e.
This sequence of text lines may include opcodes or directives. Once a macro has been defined its name may be used in place of a mnemonic. When the assembler processes such a statement, it replaces the statement with the text lines associated with that macro, then processes them as if they existed in the source code file including, in some assemblers, expansion of any macros existing in the replacement text. Macros in this sense date to IBM autocoders of the s.
Since macros can have 'short' names but expand to several or indeed many lines of code, they can be used to make assembly language programs appear to be far shorter, requiring fewer lines of source code, as with higher level languages.
They can also be used to add higher levels of structure to assembly programs, optionally introduce embedded debugging code via parameters and other similar features. Macro assemblers often allow macros to take parameters.
Some assemblers include quite sophisticated macro languages, incorporating such high-level language elements as optional parameters, symbolic variables, conditionals, string manipulation, and arithmetic operations, all usable during the execution of a given macro, and allowing macros to save context or exchange information.
Thus a macro might generate numerous assembly language instructions or data definitions, based on the macro arguments. This could be used to generate record-style data structures or "unrolled" loops, for example, or could generate entire algorithms based on complex parameters.
For instance, a "sort" macro could accept the specification of a complex sort key and generate code crafted for that specific key, not needing the run-time tests that would be required for a general procedure interpreting the specification.
An organization using assembly language that has been heavily extended using such a macro suite can be considered to be working in a higher-level language, since such programmers are not working with a computer's lowest-level conceptual elements.
The target machine would translate this to its native code using a macro assembler. Macros were used to customize large scale software systems for specific customers in the mainframe era and were also used by customer personnel to satisfy their employers' needs by making specific versions of manufacturer operating systems.
Assembly language and machine code – Gary explains
It is also possible to use solely the macro processing abilities of an assembler to generate code written in completely different languages, for example, to generate a version of a program in COBOL using a pure macro assembler program containing lines of COBOL code inside assembly time operators instructing the assembler to generate arbitrary code.
The user specifies options by coding a series of assembler macros. Assembling these macros generates a job stream to build the system, including job control language and utility control statements. This is because, as was realized in the s, the concept of "macro processing" is independent of the concept of "assembly", the former being in modern terms more word processing, text processing, than generating object code.
The concept of macro processing appeared, and appears, in the C programming language, which supports "preprocessor instructions" to set variables, and make conditional tests on their values. Note that unlike certain previous macro processors inside assemblers, the C preprocessor is not Turing-complete because it lacks the ability to either loop or "go to", the latter allowing programs to loop.
Macro parameter substitution is strictly by name: The most famous class of bugs resulting was the use of a parameter that itself was an expression and not a simple name when the macro writer expected a name.
To avoid any possible ambiguity, users of macro processors can parenthesize formal parameters inside macro definitions, or callers can parenthesize the input parameters.
The earliest example of this approach was in the Concept macro setoriginally proposed by Dr. This approach was widely accepted in the early '80s the latter days of large-scale assembly language use. The language was classified as an assembler, because it worked with raw machine elements such as opcodesregistersand memory references; but it incorporated an expression syntax to indicate execution order.
Parentheses and other special symbols, along with block-oriented structured programming constructs, controlled the sequence of the generated instructions. A-natural was built as the object language of a C compiler, rather than for hand-coding, but its logical syntax won some fans. There has been little apparent demand for more sophisticated assemblers since the decline of large-scale assembly language development.
REPEAT 20 switch rv nrandom, 9 ; generate a number between 0 and 8 mov ecx, 7 case 0 print "case 0" case ecx ; in contrast to most other programming languages, print "case 7" ; the Masm32 switch allows "variable cases" case They were once widely used for all sorts of programming.
However, by the s s on microcomputerstheir use had largely been supplanted by higher-level languages, in the search for improved programming productivity. Today assembly language is still used for direct hardware manipulation, access to specialized processor instructions, or to address critical performance issues. Typical uses are device driverslow-level embedded systemsand real-time systems.
Historically, numerous programs have been written entirely in assembly language. Many commercial applications were written in assembly language as well, including a large amount of the IBM mainframe software written by large corporations.