{
    This file is part of the Free Pascal run time library.
    Copyright (c) 2011 by the Free Pascal development team.

    Tiny heap manager for the i8086 near heap, embedded targets, etc.

    See the file COPYING.FPC, included in this distribution,
    for details about the copyright.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

 **********************************************************************}

    const
      TinyHeapMinBlock = 4*sizeof(pointer);

    type
      PTinyHeapBlock = ^TTinyHeapBlock;
      TTinyHeapBlock = record
        Size: ptruint;
        Next: PTinyHeapBlock;
        EndAddr: pointer;
      end;

    var
      TinyHeapBlocks: PTinyHeapBlock = nil;

    procedure InternalTinyFreeMem(Addr: Pointer; Size: ptruint); forward;

    function FindSize(p: pointer): ptruint;
      begin
        FindSize := PPtrUInt(p)[-1];
      end;

    function SysTinyGetMem(Size: ptruint): pointer;
      var
        p, prev: PTinyHeapBlock;
        AllocSize, RestSize: ptruint;
      begin
{$ifdef DEBUG_TINY_HEAP}
        Write('SysTinyGetMem(', Size, ')=');
{$endif DEBUG_TINY_HEAP}
        AllocSize := align(size+sizeof(ptruint), sizeof(pointer));

        p := TinyHeapBlocks;
        prev := nil;
        while assigned(p) and (p^.Size < AllocSize) do
          begin
            prev := p;
            p := p^.Next;
          end;

        if assigned(p) then
          begin
            result := @pptruint(p)[1];

            if p^.Size-AllocSize >= TinyHeapMinBlock then
              RestSize := p^.Size-AllocSize
            else
              begin
                AllocSize := p^.Size;
                RestSize := 0;
              end;

            if prev = nil then
              TinyHeapBlocks := p^.Next
            else
              prev^.next := p^.next;

            pptruint(p)^ := size;

            if RestSize > 0 then
              InternalTinyFreeMem(pointer(ptruint(p)+AllocSize), RestSize);
          end
        else
          if ReturnNilIfGrowHeapFails then
            Result := nil
          else
            HandleError(203);
{$ifdef DEBUG_TINY_HEAP}
        Writeln(ptruint(Result));
{$endif DEBUG_TINY_HEAP}
      end;

    function TinyGetAlignedMem(Size, Alignment: ptruint): pointer;
      var
        mem: Pointer;
        memp: ptruint;
      begin
        if alignment <= sizeof(pointer) then
          result := GetMem(size)
        else
          begin
            mem := GetMem(Size+Alignment-1);
            memp := align(ptruint(mem), Alignment);
            InternalTinyFreeMem(mem, ptruint(memp)-ptruint(mem));
            result := pointer(memp);
          end;
      end;

    procedure InternalTinyFreeMem(Addr: Pointer; Size: ptruint);
      var 
        b, p, prev: PTinyHeapBlock;
        concatenated: boolean;
      begin
        concatenated := true;
        while concatenated do
          begin
            concatenated := false;
            b := addr;

            b^.Next := TinyHeapBlocks;
            b^.Size := Size;
            b^.EndAddr := pointer(ptruint(addr)+size);

            if TinyHeapBlocks = nil then
              TinyHeapBlocks := b
            else
              begin
                p := TinyHeapBlocks;
                prev := nil;

                while assigned(p) do
                  begin
                    if p^.EndAddr = addr then
                      begin
                        addr:=p;
                        size:=p^.size+size;
                        if prev = nil then
                          TinyHeapBlocks:=p^.next
                        else
                          prev^.next:=p^.next;
                        concatenated:=true;
                        break;
                      end
                    else if p = b^.EndAddr then
                      begin
                        size:=p^.size+size;
                        if prev = nil then
                          TinyHeapBlocks:=p^.next
                        else
                          prev^.next:=p^.next;
                        concatenated:=true;
                        break;
                      end;
                    
                    prev := p;
                    p := p^.next;
                  end;

                if not concatenated then
                  begin
                    p := TinyHeapBlocks;
                    prev := nil;

                    while assigned(p) and (p^.Size < size) do
                      begin
                        prev := p;
                        p := p^.Next;
                      end;

                    if assigned(prev) then
                      begin
                        b^.Next := p;
                        prev^.Next := b;
                      end
                    else
                      TinyHeapBlocks := b;
                  end;
              end;
          end;
      end;

    function SysTinyFreeMem(Addr: Pointer): ptruint;
      var
        sz: ptruint;
      begin
{$ifdef DEBUG_TINY_HEAP}
        Writeln('SysTinyFreeMem(', ptruint(Addr), ')');
{$endif DEBUG_TINY_HEAP}
        if addr=nil then
          begin
            result:=0;
            exit;
          end;
        sz := Align(FindSize(addr)+SizeOf(ptruint), sizeof(pointer));

        InternalTinyFreeMem(@pptruint(addr)[-1], sz);
        
        result := sz;
      end;

    function SysTinyFreeMemSize(Addr: Pointer; Size: Ptruint): ptruint;
      begin
        result := SysTinyFreeMem(addr);
      end;

    function SysTinyMemSize(p: pointer): ptruint;
      begin
        result := findsize(p);
      end;

    function SysTinyAllocMem(size: ptruint): pointer;
      begin
        result := SysTinyGetMem(size);
        if result<>nil then
          FillChar(result^,SysTinyMemSize(result),0);
      end;

    function SysTinyReAllocMem(var p: pointer; size: ptruint):pointer;
      var
        sz: ptruint;
      begin
{$ifdef DEBUG_TINY_HEAP}
        Write('SysTinyReAllocMem(', ptruint(p), ',', size, ')=');
{$endif DEBUG_TINY_HEAP}
        if size=0 then
          result := nil
        else
          result := AllocMem(size);
        if result <> nil then
          begin
            if p <> nil then
              begin
                sz := FindSize(p);
                if sz > size then
                  sz := size;
                move(pbyte(p)^, pbyte(result)^, sz);
              end;
          end;
        SysTinyFreeMem(p);
        p := result;
{$ifdef DEBUG_TINY_HEAP}
        Writeln(ptruint(result));
{$endif DEBUG_TINY_HEAP}
      end;

    procedure RegisterTinyHeapBlock(AAddress: pointer; ASize: ptruint);
      begin
{$ifdef DEBUG_TINY_HEAP}
        Writeln('RegisterTinyHeapBlock(', ptruint(AAddress), ',', ASize, ')');
{$endif DEBUG_TINY_HEAP}
        if (ptruint(AAddress) and 1) <> 0 then
          begin
            Inc(AAddress);
            Dec(ASize);
          end;
        if (ASize and 1) <> 0 then
          Dec(ASize);
        pptruint(AAddress)^ := ASize - SizeOf(ptruint);
        FreeMem(pptruint(AAddress) + 1, ASize - SizeOf(ptruint));
      end;

    const
      TinyHeapMemoryManager: TMemoryManager = (
        NeedLock: false;  // Obsolete
        GetMem: @SysTinyGetMem;
        FreeMem: @SysTinyFreeMem;
        FreeMemSize: @SysTinyFreeMemSize;
        AllocMem: @SysTinyAllocMem;
        ReAllocMem: @SysTinyReAllocMem;
        MemSize: @SysTinyMemSize;
        InitThread: nil;
        DoneThread: nil;
        RelocateHeap: nil;
        GetHeapStatus: nil;
        GetFPCHeapStatus: nil;
      );