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6.15.17 BP compatibility: System

The following listing contains the interface of the System unit.

This unit contains only BP's more exotic routines which are not recommended to be used in new programs. Most of their functionality can be achieved by more standard means already.

Note: MemAvail and MaxAvail, provided in this unit, cannot easily be achieved by other means. However, it is not recommended to use them on any multi-tasking system at all, where memory is a shared resource. The notes in the unit give some hints about how to avoid using them.

On special request, i.e., by defining the conditionals __BP_TYPE_SIZES__, __BP_RANDOM__ and/or __BP_PARAMSTR_0__, the unit also provides BP compatible integer type sizes, a 100% BP compatible pseudo random number generator and/or BP compatible ParamStr (0) behaviour (the latter, however, only on some systems).

     { BP and partly Delphi compatible System unit for GPC
       This unit is released as part of the GNU Pascal project. It
       implements some rather exotic BP and Delphi compatibility
       features. Even many BP and Delphi programs don't need them, but
       they're here for maximum compatibility. Most of BP's and Delphi's
       System units' features are built into the compiler or the RTS.
       Note: The things in this unit are really exotic. If you haven't
       used BP or Delphi before, you don't want to look at this unit. :-)
       This unit depends on the conditional defines __BP_TYPE_SIZES__,
       __BP_RANDOM__, __BP_PARAMSTR_0__ and __BP_NO_ALLOCMEM__.
       If __BP_TYPE_SIZES__ is defined (with the -D__BP_TYPE_SIZES__
       option), the integer data types will be redefined to the sizes
       they have in BP or Delphi. Note that this might cause problems,
       e.g. when passing var parameters of integer types between units
       that do and don't use System. However, of the BP compatibility
       units, only Dos and WinDos use such parameters, and they have been
       taken care of so they work.
       If __BP_RANDOM__ is defined (-D__BP_RANDOM__), this unit will
       provide an exactly BP compatible pseudo random number generator.
       In particular, the range for integer randoms will be truncated to
       16 bits like in BP. The RandSeed variable is provided, and if it's
       set to the same value as BP's RandSeed, it produces exactly the
       same sequence of pseudo random numbers that BP's pseudo random
       number generator does (whoever might need this ... ;-). Even the
       Randomize function will behave exactly like in BP. However, this
       will not be noted unless one explicitly tests for it.
       If __BP_PARAMSTR_0__ is defined (-D__BP_PARAMSTR_0__), this
       unit will change the value of ParamStr (0) to that of
       ExecutablePath, overwriting the value actually passed by the
       caller, to imitate BP's/Dos's behaviour. However *note*: On most
       systems, ExecutablePath is *not* guaranteed to return the full
       path, so defining this symbol doesn't change anything. In general,
       you *cannot* expect to find the full executable path, so better
       don't even try it, or your program will (at best) run on some
       systems. For most cases where BP programs access their own
       executable, there are cleaner alternatives available.
       If __BP_NO_ALLOCMEM__ is defined (-D__BP_NO_ALLOCMEM__), the
       two Delphi compatible functions AllocMemCount and AllocMemSize
       will not be provided. The advantage is that this unit will not
       have to Mark the heap which makes memory de-/allocations much
       faster if the program doesn't use Mark otherwise.
       Copyright (C) 1998-2005 Free Software Foundation, Inc.
       Authors: Peter Gerwinski <>
                Prof. Abimbola A. Olowofoyeku <>
                Frank Heckenbach <>
                Dominik Freche <>
       This file is part of GNU Pascal.
       GNU Pascal is free software; you can redistribute it and/or modify
       it under the terms of the GNU General Public License as published
       by the Free Software Foundation; either version 2, or (at your
       option) any later version.
       GNU Pascal is distributed in the hope that it will be useful, but
       WITHOUT ANY WARRANTY; without even the implied warranty of
       General Public License for more details.
       You should have received a copy of the GNU General Public License
       along with GNU Pascal; see the file COPYING. If not, write to the
       Free Software Foundation, 59 Temple Place - Suite 330, Boston, MA
       02111-1307, USA.
       As a special exception, if you link this file with files compiled
       with a GNU compiler to produce an executable, this does not cause
       the resulting executable to be covered by the GNU General Public
       License. This exception does not however invalidate any other
       reasons why the executable file might be covered by the GNU
       General Public License. }
     {$if __GPC_RELEASE__ < 20030303}
     {$error This unit requires GPC release 20030303 or newer.}
     module System;
     export System = all (FileMode {$ifdef __BP_TYPE_SIZES__},
       SystemInteger => Integer, SystemWord => Word {$endif});
     import GPC (MaxLongInt => GPC_MaxLongInt);
       { Chain of procedures to be executed at the end of the program }
       ExitProc: ^procedure = nil;
       { Contains all the command line arguments passed to the program,
         concatenated, with spaces between them }
       CmdLine: CString;
       {$ifdef __BP_RANDOM__}
       { Random seed, initialized by Randomize, but can also be set
         explicitly }
       RandSeed: Integer attribute (Size = 32) = 0;
       OrigInt = Integer;
       OrigWord = Word;
       { Delphi }
       SmallInt = Integer attribute (Size = 16);
       DWord    = Cardinal attribute (Size = 32);
       { Short BP compatible type sizes if wanted }
       {$ifdef __BP_TYPE_SIZES__}
       ByteBool      = Boolean attribute (Size = 8);
       WordBool      = Boolean attribute (Size = 16);
       LongBool      = Boolean attribute (Size = 32);
       ShortInt      = Integer attribute (Size = 8);
       SystemInteger = Integer attribute (Size = 16);
       LongInt       = Integer attribute (Size = 32);
       Comp          = Integer attribute (Size = 64);
       Byte          = Cardinal attribute (Size = 8);
       SystemWord    = Cardinal attribute (Size = 16);
       LongWord      = Cardinal attribute (Size = 32);  { Delphi }
       SystemInteger = Integer;
       SystemWord    = Word;
       {$if False}  { @@ doesn't work well (dialec3.pas) -- when GPC gets
                         strings, it will be unnecessary }
       {$ifopt borland-pascal}
       String = String [255];
       MaxInt     = High (SystemInteger);
       MaxLongInt = High (LongInt);
     { Return the lowest-order byte of x }
     function  Lo (x: LongestInt): Byte;
     { Return the second-lowest-order byte of x }
     function  Hi (x: LongestInt): Byte;
     { Swap the lowest-order and second-lowest-order bytes, mask out the
       higher-order ones }
     function  Swap (x: LongestInt): SystemWord;
     { Store the current directory name (on the given drive number if
       drive <> 0) in s }
     procedure GetDir (Drive: Byte; var s: String);
     { Dummy routine for compatibility. @@Use two overloaded versions
       rather than varargs when possible. }
     procedure SetTextBuf (var f: Text; var Buf; ...);
     { Mostly useless BP compatible variables }
       SelectorInc: SystemWord = $1000;
       Seg0040: SystemWord = $40;
       SegA000: SystemWord = $a000;
       SegB000: SystemWord = $b000;
       SegB800: SystemWord = $b800;
       Test8086: Byte = 2;
       Test8087: Byte = 3;  { floating-point arithmetic is emulated
                              transparently by the OS if not present
                              in hardware }
       OvrCodeList: SystemWord = 0;
       OvrHeapSize: SystemWord = 0;
       OvrDebugPtr: Pointer = nil;
       OvrHeapOrg: SystemWord = 0;
       OvrHeapPtr: SystemWord = 0;
       OvrHeapEnd: SystemWord = 0;
       OvrLoadList: SystemWord = 0;
       OvrDosHandle: SystemWord = 0;
       OvrEmsHandle: SystemWord = $ffff;
       HeapOrg: Pointer absolute HeapLow;
       HeapPtr: Pointer absolute HeapHigh;
       HeapEnd: Pointer = Pointer (High (PtrCard));
       FreeList: Pointer = nil;
       FreeZero: Pointer = nil;
       StackLimit: SystemWord = 0;
       HeapList: SystemWord = 0;
       HeapLimit: SystemWord = 1024;
       HeapBlock: SystemWord = 8192;
       HeapAllocFlags: SystemWord = 2;
       CmdShow: SystemInteger = 0;
       SaveInt00: Pointer = nil;
       SaveInt02: Pointer = nil;
       SaveInt0C: Pointer = nil;
       SaveInt0D: Pointer = nil;
       SaveInt1B: Pointer = nil;
       SaveInt21: Pointer = nil;
       SaveInt23: Pointer = nil;
       SaveInt24: Pointer = nil;
       SaveInt34: Pointer = nil;
       SaveInt35: Pointer = nil;
       SaveInt36: Pointer = nil;
       SaveInt37: Pointer = nil;
       SaveInt38: Pointer = nil;
       SaveInt39: Pointer = nil;
       SaveInt3A: Pointer = nil;
       SaveInt3B: Pointer = nil;
       SaveInt3C: Pointer = nil;
       SaveInt3D: Pointer = nil;
       SaveInt3E: Pointer = nil;
       SaveInt3F: Pointer = nil;
       SaveInt75: Pointer = nil;
       RealModeRegs: array [0 .. 49] of Byte =
         (0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
          0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
          0, 0, 0, 0, 0, 0, 0, 0);
     { Mostly useless BP compatible pointer functions }
     function  Ofs (const x): PtrWord;
     function  Seg (const x): PtrWord;
     function  Ptr (Seg, Ofs: PtrWord): Pointer;
     function  CSeg: PtrWord;
     function  DSeg: PtrWord;
     function  SSeg: PtrWord;
     function  SPtr: PtrWord;
     { Routines to handle BP's 6 byte Real type which is formatted like
       47                                                   0
       -|------- -------- -------- -------- --------|--------
        |                                           |
        +----------+                   +------------+
       47 Sign Bit |  8..46 Mantissa   | 0..7 Biased Exponent
       This format does not support infinities, NaNs and denormalized
       numbers. The first digit after the binary point is not stored and
       assumed to be 1. (This is called the normalized representation of
       a binary floating point number.)
       In GPC, this type is represented by the type BPReal which is
       binary compatible to BP's type, and can therefore be used in
       connection with binary files used by BP programs.
       The functions RealToBPReal and BPRealToReal convert between
       this type and GPC's Real type. Apart from that, BPReal should
       be treated as opaque.
       The variables BPRealIgnoreOverflow and BPRealIgnoreUnderflow
       determine what to do in the case of overflows and underflows. The
       default values are BP compatible. }
       { Ignore overflows, and use the highest possible value instead. }
       BPRealIgnoreOverflow: Boolean = False;
       { Ignore underflows, and use 0 instead. This is BP's behaviour,
         but has the disadvantage of diminishing computation precision. }
       BPRealIgnoreUnderflow: Boolean = True;
       BPRealInteral = Cardinal attribute (Size = 8);
       BPReal = packed record
         Format: packed array [1 .. 6] of BPRealInteral
     function RealToBPReal (r: Real) = BR: BPReal;
     function BPRealToReal (const BR: BPReal) = RealValue: Real;
     { Heap management stuff }
       { Possible results for HeapError }
       HeapErrorRunError = 0;
       HeapErrorNil      = 1;
       HeapErrorRetry    = 2;
       { If assigned to a function, it will be called when memory
         allocations do not find enough free memory. Its result
         determines if a run time error should be raised (the default),
         or nil should be returned, or the allocation should be retried
         (causing the routine to be called again if the allocation still
         doesn't succeed).
         - Returning nil can cause some routines of the RTS and units
           (shipped with GPC or third-party) to crash when they don't
           expect nil, so better don't use this mechanism, but rather
           CGetMem where needed.
         - Letting the allocation be retried, of course, only makes sense
           if the routine freed some memory before -- otherwise it will
           cause an infinite loop! So, a meaningful HeapError routine
           should dispose of some temporary objects, if available, and
           return HeapErrorRetry, and return HeapErrorRunError when no
           (more) of them are available. }
       HeapError: ^function (Size: SystemWord): SystemInteger = nil;
     { Just returns HeapErrorNil. When this function is assigned to
       HeapError, GetMem and New will return a nil pointer instead of
       causing a runtime error when the allocation fails. See the comment
       for HeapError above. }
     function  HeapErrorNilReturn (Size: SystemWord): SystemInteger;
     { Return the total free memory/biggest free memory block. Except
       under Win32 and DJGPP, these are expensive routines -- try to
       avoid them. Under Win32, MaxAvail returns the same as MemAvail, so
       don't rely on being able to allocate a block of memory as big as
       MaxAvail indicates. Generally it's preferable to not use these
       functions at all in order to do a safe allocation, but just try to
       allocate the memory needed using CGetMem, and check for a nil
       result. What makes these routines unrealiable is, e.g., that on
       multi-tasking systems, another process may allocate memory after
       you've called MemAvail/MaxAvail and before you get to do the next
       allocation. Also, please note that some systems over-commit
       virtual memory which may cause MemAvail to return a value larger
       than the actual (physical plus swap) memory available. Therefore,
       if you want to be "sure" (modulo the above restrictions) that the
       memory is actually available, use MaxAvail. }
     function  MemAvail: Cardinal;
     function  MaxAvail: Cardinal;
     { Delphi compatibility }
     function  CompToDouble (x: Comp): Double;
     function  DoubleToComp (x: Double): Comp;
     {$ifndef __BP_NO_ALLOCMEM__}
     function  AllocMemCount = Count: SystemInteger;
     function  AllocMemSize = Size: SizeType;
     procedure Assert (Condition: Boolean);
     procedure DefaultAssertErrorProc (const Message, FileName: String;
       LineNumber: SystemInteger; ErrorAddr: Pointer);
       AssertErrorProc: ^procedure (const Message, FileName: String;
       LineNumber: SystemInteger; ErrorAddr: Pointer) =
       NoErrMsg: Boolean = False;