Category : Assembly Language Source Code
Archive   : XLIB20.ZIP
Filename : EXAMPLE3.ASM

;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