pia.asm

来自「开放源码的编译器open watcom 1.6.0版的源代码」· 汇编 代码 · 共 78 行

;*****************************************************************************
;*
;*                            Open Watcom Project
;*
;*    Portions Copyright (c) 1983-2002 Sybase, Inc. All Rights Reserved.
;*
;*  ========================================================================
;*
;*    This file contains Original Code and/or Modifications of Original
;*    Code as defined in and that are subject to the Sybase Open Watcom
;*    Public License version 1.0 (the 'License'). You may not use this file
;*    except in compliance with the License. BY USING THIS FILE YOU AGREE TO
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;*    available at www.sybase.com/developer/opensource.
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;*  ========================================================================
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;* Description:  WHEN YOU FIGURE OUT WHAT THIS FILE DOES, PLEASE
;*               DESCRIBE IT HERE!
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;*****************************************************************************


;========================================================================
;==     Name:           PIA,PIS                                        ==
;==     Operation:      Pointer integer add and subtract               ==
;==     Inputs:         DX:AX pointer                                  ==
;==                     CX:BX long int                                 ==
;==     Outputs:        DX:AX has DX:AX op CX:BX as  pointer           ==
;==     Volatile:       DX:AX and CX:BX                                ==
;==                                                                    ==
;========================================================================
include mdef.inc


extrn  __HShift        : byte

        modstart        pia

        xdefp   __PIA
        xdefp   __PIS

        defp    __PIS
        neg     cx              ; negate the 32 bit integer
        neg     bx              ; ...
        sbb     cx,0            ; ...

        defp    __PIA
        add     ax,bx           ; add offsets
        adc     cx,0            ; calculate overflow
        mov     bx,cx           ; shuffle overflow info bx
if (_MODEL and (_BIG_DATA or _HUGE_DATA)) and ((_MODEL and _DS_PEGGED) eq 0)
        push    ds              ; need a segment register
        mov     cx,seg __HShift ; get the huge shift value
        mov     ds,cx           ; ...
        mov     cl,ds:__HShift  ; ...
        pop     ds              ; restore register
else
        mov     cl,__HShift     ; get huge shift value
endif
        shl     bx,cl           ; adjust the overflow by huge shift value
        add     dx,bx           ; and add into selector value
        ret                     ; ...
        endproc __PIA
        endproc __PIS

        endmod
        end