July 2006 - Gpc

Inefficiency of `mod'
by Emil Jerabek 26 Oct '10

26 Oct '10

Hi, during some debugging I noticed that GPC generates very hairy code for the `mod' operator with signed arguments. A closer look revealed that the code contains a lot of branching on conditions which can be determined on compile time, and most surprisingly, the value of X mod Y is recomputed _twice_, if X is negative. (I've attached a commented assembler dump.) This may be partially a back-end problem (CSE?), but I feel there's something wrong in the relevant code in gpc-common.c (build_pascal_binary_op) as well. `exp1 mod exp2' gets translated into something like exp2 <= 0 ? error : exp1 >= 0 ? exp1 mod exp2 : ((-exp1) mod exp2) == 0 ? 0 : exp2 - (-exp1) mod exp2 This arranges that both arguments supplied to the "internal mod" are non-negative, but this information is not passed on -- the arguments are still declared as signed types, which apparently makes the back-end to produce the mess it does. I've done a little test: the following replacement for `mod', which differs from the built-in one essentially just by the type-casts to `Cardinal', inline operator xmod (X, Y: Integer) = Z: Integer; begin if Y <= 0 then RuntimeError (714); if X >= 0 then Z := Cardinal (X) mod Y else begin Z := Cardinal (-X) mod Y; if Z <> 0 then Z := Y - Z end end; indeed generates a better code, it measures about 15% faster for positive X and more than twice faster for negative X. YMMV. If this is possible in user code, it should work in the compiler internals as well :) The result type of the whole `mod' expression looks dubious too. IIUIC, `exp1 mod exp2' inherits the type of exp1. Now, the result of `mod' is guaranteed to be nonnegative and to fit in the type of exp2 (or more precisely, it is in 0 .. High (type of (exp2)) - 1), whereas it needn't have anything to do with the type of exp1: consider var X, Z: Integer; Y: LongInt; begin X := -8; Y := High (LongInt); Z := X mod Y { -> overflow } end Or am I missing something? Emil (BTW, where is fjf434c.pas?)

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New (gpc-20060325)
by Waldek Hebisch 08 Dec '09

08 Dec '09

I have put a new gpc snapshot at: http://www.math.uni.wroc.pl/~hebisch/gpc-20060325.tar.bz2 Main change is preliminary gcc-4.0.x support. The other changes are rather small. Note that for "production use" 3.4.x and 3.3.x backend are prefered. Also, using 2.8.1, 2.95.3 and 3.2.3 backend should work, but is depreciated. For more detail see: http://www.math.uni.wroc.pl/~hebisch/gpc/NEWS-20060325 and http://www.math.uni.wroc.pl/~hebisch/gpc/Fixed-20060325 -- Waldek Hebisch hebisch(a)math.uni.wroc.pl

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Memory layout of array of variable size.
by Bastiaan Veelo 24 Dec '07

24 Dec '07

Hi, In an attempt to hook up to GTK+, I am trying to pass a Pascal array of varible size to C. Static arrays are fine, but these arrays carry some additional information like capacity and size, and I gues they could be received as a struct on the C-side. However, I cannot figure out the structure that the struc should have. I do like this in Pascal: procedure YGTK_init(var argc : CInteger; argv : array of CString); external name 'YGTK_init'; procedure Y_init; var argc : CInteger; argv : array[0..ParamCount] of CString; Counter : integer; begin argc := ParamCount+1; for Counter := 0 to ParamCount do begin argv[Counter] := NewCString(ParamStr(Counter)); end; YGTK_init(argc, argv); end; And like this in C: struct t_argv { int end; void *argv; }; void YGTK_init( int *argc, struct t_argv argv ) { printf("In ygtk.c:YGTK_init.\n"); printf("argv.end: %d\n", argv2.argc); printf("argv.argv address: %p\n", argv2.argv); printf("argv.argv int: %d\n", argv2.argv); printf("argv.argv string: %s\n", argv2.argv); printf("number of arguments: %d\n", *argc); } So I figured out that the first element in the struct is an integer containing the length-1 of the array, but what it should look like for the rest I do not know yet. Do you have an idea? Thanks, Bastiaan.

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Problem with --enable-keyword and --enable-predefined-identifier
by J. David Bryan 17 Aug '06

17 Aug '06

Running gpc-20060325 on i486-pc-mingw32 (gcc-3.4.6), I wish to use an "asm" statement and the predefined identifiers "Cardinal" and "ParamCount" in an Extended Pascal program. However, the following program fails to compile: {$ extended-pascal } {$ enable-keyword asm } {$ enable-predefined-identifier Cardinal } {$ enable-predefined-identifier ParamCount } program Predefs; var C : Cardinal; I : integer; begin asm ('nop'); I := ParamCount; C := 1 end. With "gpc -c predefs.pas", I get: predefs.pas:1: warning: compiler directives are a UCSD Pascal extension predefs.pas: In main program: predefs.pas:12: error: `asm' is an extension of Borland Pascal, traditional predefs.pas:12: error: Macintosh Pascal predefs.pas:13: error: `ParamCount' is an extension of Borland Pascal Note from the above that "Cardinal" is being enabled by the directives, whereas "ParamCount" and "asm" are not. I get the same results if I specify the compiler switches on the command line (e.g., "--enable-keyword=asm", etc.) instead of within the program. I see the same behavior with gpc-20051116. Is this a compiler bug, or am I doing something wrong? -- Dave

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Dev+GNU Pascal: unrecognised escape sequence
by Bastiaan Veelo 06 Aug '06

06 Aug '06

Also, when I load an example project, e.g., C:\dev_gpc\examples\WinHello\Windows Hello.dp and try to build, I get this error three times: c:/dev_gpc/Examples/WinHello/rsrc.rc:1: unrecognised escape sequence and this line is highlighted: 500 ICON MOVEABLE PURE LOADONCALL DISCARDABLE "C:\dev_gpc\Icon\Mainicon.ico" Any ideas why? Bastiaan.

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Bug: string cannot be given an initial value
by Bastiaan Veelo 03 Aug '06

03 Aug '06

Hi, Thank you for providing GNU Pascal! In the process of migrating from Prospero Pascal to GNU Pascal, it seems I found a bug in the latter. Given the following program: program stringtest; type record_with_empty_string = record empty_string : string(127) {VALUE ''}; end; some_records_with_empty_string(length : integer) = array[1..length] of record_with_empty_string; five_records_with_empty_string = some_records_with_empty_string(5); begin end. This program compiles. But if you uncomment the initial value of empty_string, GPC complains with "initial value of discriminated schema type is of wrong type". Things like this used to work with Prospero. Is there a workaround? Thanks, Bastiaan Veelo.

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Re: Can Assert report the file name and line number?
by Bastiaan Veelo 03 Aug '06

03 Aug '06

Peter N Lewis wrote: >> I have a lot of assertions. If one of them fails, GPC only reports >> something like "assertion failed (error #306 at 40dd45)". How can I >> find out the exact assertion that failed? > > > Rather than use the built in assertions, we use our own assertions, > that way it allows us to compile them out of the later beta/final > builds (a requirement for over-asserting as recommended by Writing > Solid Code which should be essential reading for any programmer). > > The code we use is basically: > > Prefix file: > > {$definec do_debug true} > > {$ifc do_debug} > {$definec Assert(b) AssertCode((b), __FILE__, __LINE__)} > {$definec AssertNoErr(err) AssertNoErrCode((err), __FILE__, __LINE__)} > {$definec InitAssertions(name, version) InitAssertionsCode(name, > version)} > {$elsec} > {$definec Assert(b)} > {$definec AssertNoErr(err)} > {$definec InitAssertions(name, version)} > {$endc} > > > Assertions unit: > > unit MyAssertions; > > interface > > {$ifc do_debug} > procedure AssertCode( b: Boolean; const sourceFileName: String; > sourceFileLine: Integer ); > procedure AssertNoErrCode( err: OSStatus; const sourceFileName: > String; sourceFileLine: Integer ); > procedure InitAssertionsCode( const name: String; const version: > String ); > {$endc} > > implementation > > {$ifc do_debug} > > var > gAppName: String255; > gAppVersion: String255; > > procedure InitAssertionsCode( const name: String; const version: > String ); > begin > gAppName := name; > gAppVersion := version; > end; > > procedure AssertCode( b: Boolean; const sourceFileName: String; > sourceFileLine: Integer ); > begin > if not b then begin > WriteLn( 'Assert: ' + gAppName + ' ' + gAppVersion + ' - ' > + sourceFileName + ':' + NumToStr( sourceFileLine ) ); > end; > end; > > procedure AssertNoErrCode( err: OSStatus; const sourceFileName: > String; sourceFileLine: Integer ); > begin > if err <> noErr then begin > WriteLn( 'Assert: Error=' + NumToStr(err) + ' ' + gAppName > + ' ' + gAppVersion + ' - ' + sourceFileName + ':' + NumToStr( > sourceFileLine ) ); > end; > end; > > {$endc} > > > Obviously this can easily be extended to implement assertions any way > you desire. > > Please be aware that if you intend to compile out assertions (as you > should for at least some assertions), then you must never include real > code in your assert statement, eg: > > Assert( (open( ... )) == 0 ); > > Rather you need to do > > err = open( ... ); > Assert( err == 0 ); > > Why do you have to compile out some assertions? Because you should be > doing things like: > > Assert( ValidDataStructure( complex_structure ) ); > > Where ValidDataStructure is walking through your complex structure > ensuring it is all internally self consistent, which could be a > significantly time consuming task. But that does not matter as it > will be compiled out when you are performance tuning and in the > shipping version. > > The alternative is you would have to be very light weight with what > you assert, or have two different classes of assertions (perhaps by > using something like) > > {$ifc do_heavy_debug} > Assert( ValidDataStructure( complex_structure ) ); > {$endc} > > Enjoy, > Peter. > Thank you for this detailed solution. Bastiaan.

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Common OpenMP syntax?
by Florian Klaempfl 03 Aug '06

03 Aug '06

I'am currently thinking about implementing OpenMP support in FPC. However, there is currently (to my knowledge) no pascal syntax defined for OpenMp support. Do you think we can find a common syntax to simplify things for users? I've some ideas how it be done, but I want to hear other ideas first so they are maybe better if they aren't influenced by my ideas :) I started also a wiki page about it http://www.freepascal.org/wiki/index.php/OpenMP_support where ideas can be written down and shared.

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Pointer to video memory, standalone runtime
by James Buchanan 02 Aug '06

02 Aug '06

Hi there, It looks like it's not possible to declare a pointer to char and initialise it to the video memory, e.g. type VideoMemory: ^char; var VideoMemory := 0x80000; Excuse the syntax if its wrong, I'm new to Pascal. :-) I'd like to know if it's not possible to get a pointer to the video memory region on PCs will I need to modify the compiler to allow it? Or would it be easier to just write a helper routine in C or assembler and link to it instead? Also what is the calling convention used and what does the procedure activation record look like? Is it fairly easy to use an alternative standalone runtime library with GNU Pascal? I'd like to use GCC's -fstandalone and -nostdinc -nostdlib (IIRC) options to link to my own standalone runtime so I can use Pascal for low level system programming. Thanks very much. James

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Dev+GNU Pascal: internal option '--amtmpfile' not given
by Bastiaan Veelo 28 Jul '06

28 Jul '06

Hi, I am checking out Dev+GNU Pascal on Windows XP, and am having trouble compiling and linking. The problem is that when I follow the tutorial and start a GUI project, compilation halts with this error message: gpc: Internal GPC problem: internal option `--amtmpfile' not given. The project was started in a directory with a short name in C:/, to work around this other problem: I tried to compile one of the examples that get loaded upon the initial start of Dev+GNU Pascal, C:\dev_gpc\examples\projects\GrClock.pas, but compilation halted with the message c:/dev_gpc/lib/gcc-lib/ming32/3.2.3/collect2.exe: C:/Program: No such file: No such file or directory So gpc seems to try and link a file from "C:/Program Files/..." but chockes on the space in the directory name. I installed Dev+GNU Pascal from the file http://gnu-pascal.de/contrib/chief/win32/dev_gnu_pascal-1.9.4.8.exe. I followed the instructions in the Readme, and built the file build_units.pas. No compiler errors occurred, seemed to compile fine, and as far as I can see, no executable was produced (despite the warnings in the readme). What can I do to get this thing to work? Best regards, Bastiaan.

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