IJG JPEG LIBRARY:  CODING RULESCopyright (C) 1991-1996, Thomas G. Lane.This file is part of the Independent JPEG Group's software.For conditions of distribution and use, see the accompanying README file.Since numerous people will be contributing code and bug fixes, it's importantto establish a common coding style.  The goal of using similar coding stylesis much more important than the details of just what that style is.In general we follow the recommendations of "Recommended C Style and CodingStandards" revision 6.1 (Cannon et al. as modified by Spencer, Keppel andBrader).  This document is available in the IJG FTP archive (seejpeg/doc/cstyle.ms.tbl.Z, or cstyle.txt.Z for those without nroff/tbl).Block comments should be laid out thusly:/* *  Block comments in this style. */We indent statements in K&R style, e.g.,	if (test) {	  then-part;	} else {	  else-part;	}with two spaces per indentation level.  (This indentation convention ishandled automatically by GNU Emacs and many other text editors.)Multi-word names should be written in lower case with underscores, e.g.,multi_word_name (not multiWordName).  Preprocessor symbols and enum constantsare similar but upper case (MULTI_WORD_NAME).  Names should be unique withinthe first fifteen characters.  (On some older systems, global names must beunique within six characters.  We accommodate this without cluttering thesource code by using macros to substitute shorter names.)We use function prototypes everywhere; we rely on automatic source codetransformation to feed prototype-less C compilers.  Transformation is doneby the simple and portable tool 'ansi2knr.c' (courtesy of Ghostscript).ansi2knr is not very bright, so it imposes a format requirement on functiondeclarations: the function name MUST BEGIN IN COLUMN 1.  Thus all functionsshould be written in the following style:LOCAL(int *)function_name (int a, char *b){    code...}Note that each function definition must begin with GLOBAL(type), LOCAL(type),or METHODDEF(type).  These macros expand to "static type" or just "type" asappropriate.  They provide a readable indication of the routine's usage andcan readily be changed for special needs.  (For instance, special linkagekeywords can be inserted for use in Windows DLLs.)ansi2knr does not transform method declarations (function pointers instructs).  We handle these with a macro JMETHOD, defined as	#ifdef HAVE_PROTOTYPES	#define JMETHOD(type,methodname,arglist)  type (*methodname) arglist	#else	#define JMETHOD(type,methodname,arglist)  type (*methodname) ()	#endifwhich is used like this:	struct function_pointers {	  JMETHOD(void, init_entropy_encoder, (int somearg, jparms *jp));	  JMETHOD(void, term_entropy_encoder, (void));	};Note the set of parentheses surrounding the parameter list.A similar solution is used for forward and external function declarations(see the EXTERN and JPP macros).If the code is to work on non-ANSI compilers, we cannot rely on a prototypedeclaration to coerce actual parameters into the right types.  Therefore, useexplicit casts on actual parameters whenever the actual parameter type is notidentical to the formal parameter.  Beware of implicit conversions to "int".It seems there are some non-ANSI compilers in which the sizeof() operatoris defined to return int, yet size_t is defined as long.  Needless to say,this is brain-damaged.  Always use the SIZEOF() macro in place of sizeof(),so that the result is guaranteed to be of type size_t.The JPEG library is intended to be used within larger programs.  Furthermore,we want it to be reentrant so that it can be used by applications that processmultiple images concurrently.  The following rules support these requirements:1. Avoid direct use of file I/O, "malloc", error report printouts, etc;pass these through the common routines provided.2. Minimize global namespace pollution.  Functions should be declared staticwherever possible.  (Note that our method-based calling conventions help thisa lot: in many modules only the initialization function will ever need to becalled directly, so only that function need be externally visible.)  Allglobal function names should begin with "jpeg_", and should have anabbreviated name (unique in the first six characters) substituted by macrowhen NEED_SHORT_EXTERNAL_NAMES is set.3. Don't use global variables; anything that must be used in another moduleshould be in the common data structures.4. Don't use static variables except for read-only constant tables.  Variablesthat should be private to a module can be placed into private structures (seethe system architecture document, structure.doc).5. Source file names should begin with "j" for files that are part of thelibrary proper; source files that are not part of the library, such as cjpeg.cand djpeg.c, do not begin with "j".  Keep source file names to eightcharacters (plus ".c" or ".h", etc) to make life easy for MS-DOSers.  Keepcompression and decompression code in separate source files --- someapplications may want only one half of the library.Note: these rules (particularly #4) are not followed religiously in themodules that are used in cjpeg/djpeg but are not part of the JPEG libraryproper.  Those modules are not really intended to be used in otherapplications.