Magic number (programming) - Wikipedia. In computer programming, the term magic number has multiple meanings. It could refer to one or more of the following: A constant numerical or text value used to identify a file format or protocol; for files, see List of file signatures. Distinctive unique values that are unlikely to be mistaken for other meanings (e. Globally Unique Identifiers)Unique values with unexplained meaning or multiple occurrences which could (preferably) be replaced with named constants. Format indicator.

1. Get the latest breaking news across the U.S.
2. Free hippie movement papers, essays, and research papers.
3. 00-00-00: xerox corporation: 00-00-01: xerox corporation: 00-00-02: xerox corporation: 00-00-03: xerox corporation: 00-00-04: xerox corporation: 00-00-05: xerox.

With the development of paged versions of Unix, a header was created to describe the executable image components. Also, a branch instruction was inserted as the first word of the header to skip the header and start the program. In this way a program could be run in the older relocatable memory reference (regular) mode or in paged mode. As more executable formats were developed, new constants were added by incrementing the branch offset. The first 8 bytes of the file was a header containing the sizes of the program (text) and initialized (global) data areas. Also, the first 1. Adding seven to the program counter showed that if this constant was executed, it would branch the Unix exec() service over the executable image eight byte header and start the program.

The new MSN, Your customizable collection of the best in news, sports, entertainment, money, weather, travel, health, and lifestyle, combined with Outlook, Facebook.

Philly Antifa is a Antifascist division operating in Philadelphia, PA and the surrounding area. We are in direct conflict with Racism, Homophobia, Sexism, Anti.

Since the Sixth and Seventh Editions of Unix employed paging code, the dual role of the header constant was hidden. That is, the exec() service read the executable file header (meta) data into a kernel space buffer, but read the executable image into user space, thereby not using the constant's branching feature. Magic number creation was implemented in the Unix linker and loader and magic number branching was probably still used in the suite of stand- alonediagnostic programs that came with the Sixth and Seventh Editions. Thus, the header constant did provide an illusion and met the criteria for magic. In Version Seven Unix, the header constant was not tested directly, but assigned to a variable labeled ux. Probably because of its uniqueness, the term magic number came to mean executable format type, then expanded to mean file system type, and expanded again to mean any type of file.

Magic numbers in files. Magic numbers implement strongly typed data and are a form of in- band signaling to the controlling program that reads the data type(s) at program run- time.

Many files have such constants that identify the contained data. Detecting such constants in files is a simple and effective way of distinguishing between many file formats and can yield further run- time information. Examples. Compiled. Java class files (bytecode) and Mach- O binaries start with hex CAFEBABE. When compressed with Pack. CAFED0. 0D. GIF image files have the ASCII code for .

JPEG/JFIF files contain the ASCII code for . JPEG/Exif files contain the ASCII code for .

That signature contains various newline characters to permit detecting unwarranted automated newline conversions, such as transferring the file using FTP with the ASCIItransfer mode instead of the binary mode. The definition allows the uncommon . This magic number encodes a bitmap of the Nintendo logo. Amiga software executable Hunk files running on Amiga classic 6. II is for Intel, which uses little endian byte ordering, so the magic number is 4.

A 0. 0. MM is for Motorola, which uses big endian byte ordering, so the magic number is 4. D 4. D 0. 0 2. A. Unicode text files encoded in UTF- 1. Byte Order Mark to detect endianness (FE FF for big endian and FF FE for little endian). And on Microsoft Windows, UTF- 8 text files often start with the UTF- 8 encoding of the same character, EF BB BF. LLVM Bitcode files start with BC (0x.

WAD files start with IWAD or PWAD (for Doom), WAD2 (for Quake) and WAD3 (for Half- Life). Microsoft Compound File Binary Format (mostly known as one of the older formats of Microsoft Office documents) files start with D0 CF 1. E0, which is visually suggestive of the word . The Windows utility Tr.

ID has a similar purpose. Magic numbers in protocols. In UDP- based MSRPC requests the first byte is always 0.

In COM and DCOM marshalled interfaces, called OBJREFs, always start with the byte sequence . Debugging extensions (used for DCOM channel hooking) are prefaced with the byte sequence . Currently E3 represents an e. Donkey client, C5 represents e. Mule, and D4 represents compressed e. Mule. SSL transactions always begin with a .

The record encapsulation scheme used to prefix all SSL packets consists of two- and three- byte header forms. Typically an SSL version 2 client hello message is prefixed with a 8. Free Dating In Yakima here. SSLv. 3 server response to a client hello begins with 1.

DHCP packets use a . This value is included in all DHCP packet types. HTTP/2 connections are opened with the preface '0x. The preface is designed to avoid the processing of frames by servers and intermediaries which support earlier versions of HTTP but not 2.

Magic numbers in other uses. This has been referred to as breaking one of the oldest rules of programming, dating back to the COBOL, FORTRAN and PL/1 manuals of the 1.

An example of a non- intuitively named constant is int EIGHT = 1. NUMBER. In the preceding example, 5. It is considered better programming style to write the following: constantint deck. Size : = 5. 2. for i from 1 to deck. Size. j : = i + random. Int(deck. Size + 1 - i) - 1. Entries(i, j). This is preferable for several reasons: It is easier to read and understand.

A programmer reading the first example might wonder, What does the number 5. The programmer might infer the meaning after reading the code carefully, but it is not obvious. Magic numbers become particularly confusing when the same number is used for different purposes in one section of code. It is easier to alter the value of the number, as it is not duplicated.

Changing the value of a magic number is error- prone, because the same value is often used several times in different places within a program. Also, when two semantically distinct variables or numbers have the same value they may be accidentally both edited together. To modify the first example to shuffle a Tarot deck, which has 7. This would cause two problems. First, it would miss the value 5. Second, it would likely replace the characters .

By contrast, changing the value of the deck. Size variable in the second example would be a simple, one- line change. The declarations of .

For example, to generalize the above example into a procedure that shuffles a deck of any number of cards, it would be sufficient to turn deck. Size into a parameter of that procedure, whereas the first example would require several changes.

Size). for i from 1 to deck. Size. j : = i + random. Int(deck. Size + 1 - i) - 1. Entries(i, j). It helps detect typos. Using a variable (instead of a literal) takes advantage of a compiler's checking. Accidentally typing . If an IDE supports code completion, it will fill in most of the variable's name from the first few letters.

Disadvantages are: When the named constant is not defined near its use it hurts the locality (and thus comprehensibility) of the code. Putting the 5. 2 in a possibly distant place means that to understand the workings of the for loop completely (for example to estimate the run- time of the loop) one must track down the definition and verify that it is the expected number. It makes the code more verbose.

An increase in verbosity may be justified when there is some likelihood of confusion about the constant, or when there is a likelihood the constant may need to be changed, such as reuse of a shuffling routine for other card games. It may be slower to process the expression . There is therefore usually no speed penalty compared to using magic numbers in code. It can increase the line length of the source code, forcing lines to be broken up when many constants are used on the same line. It can make debugging more difficult on systems where the debugger doesn't display the values of constants. Accepted limited use of magic numbers.

While such acceptance is subjective, and often depends on individual coding habits, the following are common examples: the use of 0 and 1 as initial or incremental values in a for loop, such as for (int i = 0; i < max; i += 1) (assuming ++i is not supported)the use of 2 to check whether a number is even or odd, as in is. Even = (x % 2 == 0), where % is the modulo operatorthe use of simple arithmetic constants, e. Math. PI * radius.

Most modern programming languages provide a boolean or boolprimitive type and so the use of 0 and 1 is ill- advised. In C and C++, 0 is sometimes used to represent the null pointer.

As with boolean values, the C standard library includes a macro definition NULL whose use is encouraged. Other languages provide a specific null or nil value and when this is the case no alternative should be used.

The typed pointer constant nullptr has been introduced with C++1. Magic GUIDs. They should only be generated by a reputable software tool. Memory is usually viewed in hexadecimal, so memorable repeating or hexspeak values are common. Numerically odd values may be preferred so that processors without byte addressing will fault when attempting to use them as pointers (which must fall at even addresses).

Values should be chosen that are away from likely addresses (the program code, static data, heap data, or the stack). Similarly, they may be chosen so that they are not valid codes in the instruction set for the given architecture.

Since it is very unlikely, although possible, that a 3. Famous and common examples include: Code. Description. FACADE. CC resembles the opcode of the INT 3 debug breakpoint interrupt on x. CDCDCDCDUsed by Microsoft's C/C++ debug malloc() function to mark uninitialized heap memory, usually returned from Heap. Alloc(). On Sun Microsystems' Solaris, marks freed kernel memory (KMEM. On Sun Microsystems' Solaris, marks the red zone (KMEM.

Some IP cameras expecting that the player sends this magic number and do not start the stream if no magic number received.