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| -rw-r--r-- | gc/doc/README.macros | 78 |
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diff --git a/gc/doc/README.macros b/gc/doc/README.macros deleted file mode 100644 index d9df8dd..0000000 --- a/gc/doc/README.macros +++ /dev/null @@ -1,78 +0,0 @@ -The collector uses a large amount of conditional compilation in order to -deal with platform dependencies. This violates a number of known coding -standards. On the other hand, it seems to be the only practical way to -support this many platforms without excessive code duplication. - -A few guidelines have mostly been followed in order to keep this manageable: - -1) #if and #ifdef directives are properly indented whenever easily possible. -All known C compilers allow whitespace between the "#" and the "if" to make -this possible. ANSI C also allows white space before the "#", though we -avoid that. It has the known disadvantages that it differs from the normal -GNU conventions, and that it makes patches larger than otherwise necessary. -In my opinion, it's still well worth it, for the same reason that we indent -ordinary "if" statements. - -2) Whenever possible, tests are performed on the macros defined in gcconfig.h -instead of directly testing patform-specific predefined macros. This makes it -relatively easy to adapt to new compilers with a different set of predefined -macros. Currently these macros generally identify platforms instead of -features. In many cases, this is a mistake. - -3) The code currently avoids #elif, eventhough that would make it more -readable. This was done since #elif would need to be understood by ALL -compilers used to build the collector, and that hasn't always been the case. -It makes sense to reconsider this decision at some point, since #elif has been -standardized at least since 1989. - -Many of the tested configuration macros are at least somewhat defined in -either include/private/gcconfig.h or in Makefile.direct. Here is an attempt -at defining some of the remainder: (Thanks to Walter Bright for suggesting -this. This is a work in progress) - -MACRO EXPLANATION ------ ----------- - -__DMC__ Always #define'd by the Digital Mars compiler. Expands - to the compiler version number in hex, i.e. 0x810 is - version 8.1b0 - -_ENABLE_ARRAYNEW - #define'd by the Digital Mars C++ compiler when - operator new[] and delete[] are separately - overloadable. Used in gc_cpp.h. - -_MSC_VER Expands to the Visual C++ compiler version. Assumed to - not be defined for other compilers (at least if they behave - appreciably differently). - -_DLL Defined by Visual C++ if dynamic libraries are being built - or used. Used to test whether __declspec(dllimport) or - __declspec(dllexport) needs to be added to declarations - to support the case in which the collector is in a dll. - -GC_DLL User-settable macro that forces the effect of _DLL. - -GC_NOT_DLL User-settable macro that overrides _DLL, e.g. if dynamic - libraries are used, but the collector is in a static library. - -__STDC__ Assumed to be defined only by compilers that understand - prototypes and other C89 features. Its value is generally - not used, since we are fine with most nonconforming extensions. - -SUNOS5SIGS Solaris-like signal handling. This is probably misnamed, - since it really doesn't guarantee much more than Posix. - Currently set only for Solaris2.X, HPUX, and DRSNX. Should - probably be set for some other platforms. - -PCR Set if the collector is being built as part of the Xerox - Portable Common Runtime. - -SRC_M3 Set if the collector is being built as a replacement of the - one in the DEC/Compaq SRC Modula-3 runtime. I suspect this - was last used around 1994, and no doubt broke a long time ago. - It's there primarily incase someone wants to port to a similar - system. - - - |