Machine code - Wikipedia
One example is MASM from Microsoft; it generates code for the x86 series of processors. that my own work involves a good degree of machine level programming. Is there any relation between switching frequency and sample rate or else. What Is This Book About? This book is about the disassembly of x86 machine code into human-readable assembly, and the decompilation of x86 assembly code. It is not just a single language, but rather a group of languages. An assembly language implements a symbolic representation of the machine code needed to .
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.
Assembly language - Wikipedia
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. 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.Classification Of Computer Languages Chapter 15 for SBI PO / IBPS / Clerk / SO and Other Gov Exams
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.
Most early microcomputers relied on hand-coded assembly language, including most operating systems and large applications. This was because these systems had severe resource constraints, imposed idiosyncratic memory and display architectures, and provided limited, buggy system services.
Perhaps more important was the lack of first-class high-level language compilers suitable for microcomputer use. A psychological factor may have also played a role: In a more commercial context, the biggest reasons for using assembly language were minimal bloat sizeminimal overhead, greater speed, and reliability. According to some[ who? This was in large part because interpreted BASIC dialects on these systems offered insufficient execution speed, as well as insufficient facilities to take full advantage of the available hardware on these systems.
Some systems even have an integrated development environment IDE with highly advanced debugging and macro facilities. Some compilers available for the Radio Shack TRS and its successors had the capability to combine inline assembly source with high-level program statements. Upon compilation a built-in assembler produced inline machine code.
Current usage[ edit ] There have always been debates over the usefulness and performance of assembly language relative to high-level languages. Assembly language has specific niche uses where it is important; see below. In the case of speed optimization, modern optimizing compilers are claimed  to render high-level languages into code that can run as fast as hand-written assembly, despite the counter-examples that can be found.
This has made raw code execution speed a non-issue for many programmers. There are some situations in which developers might choose to use assembly language: A stand-alone executable of compact size is required that must execute without recourse to the run-time components or libraries associated with a high-level language; this is perhaps the most common situation.
For example, firmware for telephones, automobile fuel and ignition systems, air-conditioning control systems, security systems, and sensors. Code that must interact directly with the hardware, for example in device drivers and interrupt handlers. In an embedded processor or DSP, high-repetition interrupts require the shortest number of cycles per interrupt, such as an interrupt that occurs or times a second.
Programs that need to use processor-specific instructions not implemented in a compiler. A stack machine has most or all of its operands on an implicit stack. Special purpose instructions also often lack explicit operands CPUID in the x86 architecture writes values into four implicit destination registers, for instance. This distinction between explicit and implicit operands is important in code generators, especially in the register allocation and live range tracking parts.
A good code optimizer can track implicit as well as explicit operands which may allow more frequent constant propagationconstant folding of registers a register assigned the result of a constant expression freed up by replacing it by that constant and other code enhancements. Programs[ edit ] A computer program is a list of instructions that can be executed by a central processing unit. A program's execution is done in order for the CPU that is executing it to solve a specific problem and thus accomplish a specific result.
While simple processors are able to execute instructions one after another, superscalar processors are capable of executing a variety of different instructions at once.
Program flow may be influenced by special 'jump' instructions that transfer execution to an instruction other than the numerically following one. Conditional jumps are taken execution continues at another address or not execution continues at the next instruction depending on some condition.
Assembly language A much more readable rendition of machine language, called assembly languageuses mnemonic codes to refer to machine code instructions, rather than using the instructions' numeric values directly. Example[ edit ] The MIPS architecture provides a specific example for a machine code whose instructions are always 32 bits long. The general type of instruction is given by the op operation field, the highest 6 bits.
J-type jump and I-type immediate instructions are fully specified by op. R-type register instructions include an additional field funct to determine the exact operation. The fields used in these types are: For example, adding the registers 1 and 2 and placing the result in register 6 is encoded: This is done to facilitate porting of machine language programs between different models.
Using microcode to implement an emulator enables the computer to present the architecture of an entirely different computer. Relationship to bytecode[ edit ] Machine code is generally different from bytecode also known as p-codewhich is either executed by an interpreter or itself compiled into machine code for faster direct execution.