Definitions

feed face

Hexspeak

Hexspeak, like leetspeak, is a novelty form of variant English spelling.

Hexspeak was created by programmers who wanted a magic number, a clear and unique identifier with which to mark memory or data. Using hexadecimal notation, which includes the digits 0123456789ABCDEF, it is possible to create small words with the digit "0" representing the letter "O", "1" representing the letter "I", and "5" representing "S".

Notable magic numbers

Many computer processors, operating systems, and debuggers make use of magic numbers, especially as a magic debug value.

  • 0xABADBABE ("a bad babe") is used by Apple as the "Boot Zero Block" magic number.
  • 0xBAADF00D ("bad food") is used by Microsoft's LocalAlloc(LMEM_FIXED) to indicate uninitialised allocated heap memory.
  • 0xBADDCAFE ("bad cafe") is used by 'watchmalloc' in OpenSolaris to mark allocated but uninitialized memory.
  • 0xCAFEBABE ("cafe babe") is used by both Mach-O ("Fat binary" in both 68k and PowerPC) to identify object files and the Java programming language to identify Java bytecode class files
  • 0xDEADBEEF ("dead beef") is used by IBM RS/6000 systems, Mac OS on 32-bit PowerPC processors and the Commodore Amiga as a magic debug value. On Sun Microsystems' Solaris, marks freed kernel memory. On OpenVMS, running on Alpha processes DEAD_BEEF can be seen by pressing CTRL-T.
  • 0xDEFEC8ED ("defecated") is the magic number for OpenSolaris core dumps.
  • 0xFEE1DEAD ("feel dead") is used as magic number in Linux reboot system call.
  • 0xFEEDFACE ("feed face") is used as a header for Mach-O binaries, and as an invalid pointer value for 'watchmalloc' in OpenSolaris.

Designing magic numbers

Given there are at least a few hundred words in English consisting of only the letters "a", "b", "c", "d", "e", "f", "o", "i" and "s", it is easy for programmers to devise their own, such as 0xD15EA5ED or 0xBED51DE5. As such, it is useful to observe a few patterns in the classic hexspeak constants given above. These constants all use the full width of the word (in this case 32-bit), and none begin with "1" or "5". This choice means that if the word is interpreted as an integer, it is a (usually large) negative integer. For example, 0xBAADF00D is -1163005939, a large negative integer that is unlikely to arise in many programs. Microsoft's 0xBAADF00D is also a good value to catch access to uninitialised memory for another reason—ending the word with the "1", "5", "b", "d", or "f" ensures that the constant is an odd number, which generates an unaligned pointer exception on many processor architectures if the constant is interpreted as a pointer value.

Alternative letters

  • The C programming language notation uses the "0x" prefix to indicate a hexadecimal number; the "0x" is usually ignored when reading the letters.
  • In the Intel assembly language, hexadecimal numbers are denoted by a "h" suffix. For example: FEEDADEADF15h ("feed a dead fish"). Note that numbers in this notation that begin with a letter have to start with a zero to distinguish them from variable names. "FEEDADEADF15h" would then be "0FEEDADEADF15h".
  • In the Pascal programming language, hexadecimal numbers are denoted by a "$" prefix. This allows words starting with the letter "S", for example $EED ("seed").

See also

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