example2.asm

DOS保护模式下汇编程序设计.zip

;The following library should be combined with XLIB.LIB using the Microsoft
;LINK and LIB utilities.  If BASIC is to be executed from the QBX
;environment, then a quick library must be loaded with the environment.  See
;BASIC documentation for instructions.


               .MODEL         LARGE,PASCAL
               .386P

               INCLUDE        XLIB.INC

CSEG           SEGMENT PARA PUBLIC USE16 'CODE'
               ASSUME CS:CSEG, DS:DSEG

;Function to calculate linear address from segment address on stack.
;Returns linear address in DX:AX.
LINADR         PROC FAR PUBLIC,
               SEGADR:DWORD                  ;Segment address of variable
               XOR            EAX,EAX        ;Clear high words
               XOR            EDX,EDX
               MOV            AX,WORD PTR SEGADR[0]
               MOV            DX,WORD PTR SEGADR[2]
               SHL            EDX,4          ;Calculate linear address
               ADD            EDX,EAX
               MOV            AX,DX
               SHR            EDX,16         ;Return linear address in DX:AX
               RET
LINADR         ENDP

;Structure defining control block for SUMARRAY.
ARRAYDATA      STRUCT
  CONDCODE     DWORD          0              ;Condition code
  N            DWORD          0              ;Number of elements to sum
  ADDRESS      DWORD          0              ;Address of first element
  SUM          DWORD          0              ;Sum of array elements
ARRAYDATA      ENDS

;Real-mode interface to SUMARRAY32.  Segment address of control block having
;structure ARRAYDATA should be on the stack.
SUMARRAY       PROC FAR PUBLIC,
               CBSEGADR:DWORD                ;Control block segment address
               PUSH           DS
               PUSHW          DSEG
               POP            DS
               XOR            EAX,EAX        ;Clear high words
               XOR            EDX,EDX
               MOV            AX,WORD PTR CBSEGADR[2]
               MOV            DX,WORD PTR CBSEGADR[0]
               SHL            EAX,4          ;Calculate linear address
               ADD            EAX,EDX
               MOV            CCODEPTR,EAX   ;Reset condition code address
               POP            DS             ;Pop calling DS
               PUSHD          OFFSET SUMARRAY32
               CALL           ENTERPM        ;Execute SUMARRAY32 in protected
               RET
SUMARRAY       ENDP

CSEG           ENDS

TSEG           SEGMENT PARA PUBLIC USE32 'CODE'
               ASSUME CS:TSEG, SS:TSEG, DS:TSEG, ES:TSEG, FS:DSEG, GS:DGROUP

;Sum the elements of a single precision array.  Array parameters are stored
;in a control block having structure of ARRAYDATA.  The linear address of the
;control block is stored at CCODEPTR.  An error code of -1 is returned in the
;condition code of the control block if the number of array elements is zero
;XLIB places an error code in the control block if an FPU exception occurs
;while calculating the sum.  This error code will have the FPU status word in
;the high word and the XLIB FPU error code in the low word.  Observe that this
;routine will be called with DS = FLATDSEL (flat-model data descriptor) and
;FS = DSEGSEL (DSEG data descriptor).
SUMARRAY32     PROC NEAR
               MOV            EBX,FS:CCODEPTR               ;Get control block
               MOV            EDX,ARRAYDATA.ADDRESS[EBX]    ;Get array address
               MOV            ESI,ARRAYDATA.N[EBX]          ;Get N
               SUB            ESI,1
               JB             NODATA                        ;Error:  N = 0
               FLDZ                                         ;Initialize sum
SUMLOOP:       FADD           DWORD PTR [EDX+4*ESI]
               SUB            ESI,1
               JAE            SUMLOOP
               FSTP           ARRAYDATA.SUM[EBX]            ;Save sum
               RET
NODATA:        MOV            ARRAYDATA.CONDCODE[EBX],-1    ;Record error code
               RET
SUMARRAY32     ENDP

TSEG           ENDS
               END