; Simple text editor - fasm example program

format PE GUI 4.0
entry start

include 'win32a.inc'

IDM_NEW   = 101
IDM_EXIT  = 102
IDM_ABOUT = 901

section '.text' code readable executable

  start:

        mov     word[esp-2],0x037F
        fldcw   word[esp-2]

        fstcw   word[cw]
;        invoke  sprintf,message,messageformat,[cw]
        mov     edi,message
        mov     cx,word[cw]
   @@:  mov     al,'0'
        shr     cx,1
        adc     al,0
        stosb
        test    cx,cx
        jnz     @b
        mov     al,0
        stosb

        invoke  MessageBox,NULL,message,NULL,MB_OK



        invoke  GetModuleHandle,0
        mov     [wc.hInstance],eax
        invoke  LoadIcon,eax,17
        mov     [wc.hIcon],eax
        invoke  LoadCursor,0,IDC_ARROW
        mov     [wc.hCursor],eax
        invoke  RegisterClass,wc
        test    eax,eax
        jz      error

        invoke  LoadMenu,[wc.hInstance],37
        invoke  CreateWindowEx,0,_class,_title,WS_VISIBLE+WS_OVERLAPPEDWINDOW,144,128,256,256,NULL,eax,[wc.hInstance],NULL
        test    eax,eax
        jz      error

        fstcw   word[cw]
;        invoke  sprintf,message,messageformat,[cw]
        mov     edi,message
        mov     cx,word[cw]
   @@:  mov     al,'0'
        shr     cx,1
        adc     al,0
        stosb
        test    cx,cx
        jnz     @b
        mov     al,0
        stosb

        invoke  MessageBox,NULL,message,NULL,MB_OK



  msg_loop:
        invoke  GetMessage,msg,NULL,0,0
        cmp     eax,1
        jb      end_loop
        jne     msg_loop
        invoke  TranslateMessage,msg
        invoke  DispatchMessage,msg
        jmp     msg_loop

  error:
        invoke  MessageBox,NULL,_error,NULL,MB_ICONERROR+MB_OK

  end_loop:
        invoke  ExitProcess,[msg.wParam]

proc WindowProc hwnd,wmsg,wparam,lparam
        push    ebx esi edi
        cmp     [wmsg],WM_CREATE
        je      .wmcreate
        cmp     [wmsg],WM_SIZE
        je      .wmsize
        cmp     [wmsg],WM_SETFOCUS
        je      .wmsetfocus
        cmp     [wmsg],WM_COMMAND
        je      .wmcommand
        cmp     [wmsg],WM_DESTROY
        je      .wmdestroy
  .defwndproc:
        invoke  DefWindowProc,[hwnd],[wmsg],[wparam],[lparam]
        jmp     .finish
  .wmcreate:
        invoke  GetClientRect,[hwnd],client
        invoke  CreateWindowEx,WS_EX_CLIENTEDGE,_edit,0,WS_VISIBLE+WS_CHILD+WS_HSCROLL+WS_VSCROLL+ES_AUTOHSCROLL+ES_AUTOVSCROLL+ES_MULTILINE,[client.left],[client.top],[client.right],[client.bottom],[hwnd],0,[wc.hInstance],NULL
        or      eax,eax
        jz      .failed
        mov     [edithwnd],eax
        invoke  CreateFont,16,0,0,0,0,FALSE,FALSE,FALSE,ANSI_CHARSET,OUT_RASTER_PRECIS,CLIP_DEFAULT_PRECIS,DEFAULT_QUALITY,FIXED_PITCH+FF_DONTCARE,NULL
        or      eax,eax
        jz      .failed
        mov     [editfont],eax
        invoke  SendMessage,[edithwnd],WM_SETFONT,eax,FALSE
        xor     eax,eax
        jmp     .finish
      .failed:
        or      eax,-1
        jmp     .finish
  .wmsize:
        invoke  GetClientRect,[hwnd],client
        invoke  MoveWindow,[edithwnd],[client.left],[client.top],[client.right],[client.bottom],TRUE
        xor     eax,eax
        jmp     .finish
  .wmsetfocus:
        invoke  SetFocus,[edithwnd]
        xor     eax,eax
        jmp     .finish
  .wmcommand:
        mov     eax,[wparam]
        and     eax,0FFFFh
        cmp     eax,IDM_NEW
        je      .new
        cmp     eax,IDM_ABOUT
        je      .about
        cmp     eax,IDM_EXIT
        je      .wmdestroy
        jmp     .defwndproc
      .new:
        invoke  SendMessage,[edithwnd],WM_SETTEXT,0,0
        jmp     .finish
      .about:
        invoke  MessageBox,[hwnd],_about_text,_about_title,MB_OK
        jmp     .finish
  .wmdestroy:
        invoke  DeleteObject,[editfont]
        invoke  PostQuitMessage,0
        xor     eax,eax
  .finish:
        pop     edi esi ebx
        ret
endp


section '.data' data readable writeable

  _title TCHAR 'MiniPad',0
  _about_title TCHAR 'About MiniPad',0
  _about_text TCHAR 'This is Win32 example program created with flat assembler.',0
  _error TCHAR 'Startup failed.',0



  _class TCHAR 'MINIPAD32',0
  _edit TCHAR 'EDIT',0

  wc WNDCLASS 0,WindowProc,0,0,NULL,NULL,NULL,COLOR_BTNFACE+1,NULL,_class

  edithwnd dd ?
  editfont dd ?

  msg MSG
  client RECT


rb 100
align 4
  cw dd 0
  message rb 100
  messageformat db 'control word: 0x%.8X',0,0


section '.idata' import data readable writeable

  library kernel,'KERNEL32.DLL',\
          user,'USER32.DLL',\
          gdi,'GDI32.DLL';,\
          ;msvcrt,'MSVCRT.DLL'

  import kernel,\
         GetModuleHandle,'GetModuleHandleA',\
         ExitProcess,'ExitProcess'

  import user,\
         RegisterClass,'RegisterClassA',\
         CreateWindowEx,'CreateWindowExA',\
         DefWindowProc,'DefWindowProcA',\
         SetWindowLong,'SetWindowLongA',\
         RedrawWindow,'RedrawWindow',\
         GetMessage,'GetMessageA',\
         TranslateMessage,'TranslateMessage',\
         DispatchMessage,'DispatchMessageA',\
         SendMessage,'SendMessageA',\
         LoadCursor,'LoadCursorA',\
         LoadIcon,'LoadIconA',\
         LoadMenu,'LoadMenuA',\
         GetClientRect,'GetClientRect',\
         MoveWindow,'MoveWindow',\
         SetFocus,'SetFocus',\
         MessageBox,'MessageBoxA',\
         PostQuitMessage,'PostQuitMessage'

  import gdi,\
         CreateFont,'CreateFontA',\
         DeleteObject,'DeleteObject'

;  import msvcrt,\
;         sprintf,'sprintf'

section '.rsrc' resource data readable

  ; resource directory

  directory RT_MENU,menus,\
            RT_ICON,icons,\
            RT_GROUP_ICON,group_icons,\
            RT_VERSION,versions

  ; resource subdirectories

  resource menus,\
           37,LANG_ENGLISH+SUBLANG_DEFAULT,main_menu

  resource icons,\
           1,LANG_NEUTRAL,icon_data

  resource group_icons,\
           17,LANG_NEUTRAL,main_icon

  resource versions,\
           1,LANG_NEUTRAL,version

  menu main_menu
       menuitem '&File',0,MFR_POPUP
                menuitem '&New',IDM_NEW
                menuseparator
                menuitem 'E&xit',IDM_EXIT,MFR_END
       menuitem '&Help',0,MFR_POPUP + MFR_END
                menuitem '&About...',IDM_ABOUT,MFR_END

  icon main_icon,icon_data,'minipad.ico'

  versioninfo version,VOS__WINDOWS32,VFT_APP,VFT2_UNKNOWN,LANG_ENGLISH+SUBLANG_DEFAULT,0,\
              'FileDescription','MiniPad - example program',\
              'LegalCopyright','No rights reserved.',\
              'FileVersion','1.0',\
              'ProductVersion','1.0',\
              'OriginalFilename','MINIPAD.EXE'
    

Floating point control word and MXCSR register
The floating point control word and bit 6-15 of the MXCSR register must be saved and
restored before any call or return by any procedure that needs to modify them, except for
procedures that have the purpose of changing these.

Mmmhhh, maybe this explains why is this happening?

Have you tried setting the control word to the minimum precision to see if it is also reset to Windows' default?

By default, _controlfp's precision control is set to 53 bits (_PC_53). Linking with FP10.OBJ changes the default precision control to 64 bits (_PC_64). On the linker command line, FP10.OBJ must appear before LIBC.LIB, LIBCMT.LIB, or MSVCRT.LIB.

It happened to me on XP sp 3, but I'm glad its nothing that I am doing wrong. I just won't expect windows to preserve certain things.

The register state also includes the x87 FPU control word. The calling convention dictates this register to be nonvolatile.

The x87 FPU control word register is set to the following standard values at the start of program execution:

FPCSR[0:6]: Exception masks all 1's (all exceptions masked)
FPCSR[7]: Reserved – 0
FPCSR[8:9]: Precision Control – 10B (double precision)
FPCSR[10:11]: Rounding control - 0 (round to nearest)
FPCSR[12]: Infinity control – 0 (not used)

A callee that modifies any of the fields within FPCSR must restore them before returning to its caller. Furthermore, a caller that has modified any of these fields must restore them to their standard values before invoking a callee unless by agreement the callee expects the modified values.

There are two exceptions to the rules regarding the non-volatility of the control flags: