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PsL Monthly 1993 December
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PSL Monthly Shareware CD-ROM (December 1993).iso
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EXTSUB.S
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1993-01-05
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847b
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43 lines
; Subtract source from dest (both 64-bit numbers)
;
; Tim Victor, January 5, 1993
;
; Callable from C as follows:
; int ExtSub(src, dest);
; always return 0
;
.model small
.code
public _ExtSub
_ExtSub proc near
push bp ; save caller's stack frame
mov bp,sp ; address stack frame of this call
push si
push di
; just subtract four pairs of words
mov si,[bp+4] ; source address
mov di,[bp+6] ; dest address
mov ax,[si]
sub [di],ax
mov ax,[si+2]
sbb [di+2],ax
mov ax,[si+4]
sbb [di+4],ax
mov ax,[si+4]
sbb [di+4],ax
sub ax,ax ; return 0
pop di
pop si
pop bp
ret
_ExtSub endp
end