Category : Dbase (Clipper, FoxBase, etc) Languages Source Code
Archive   : ASMFILE.ZIP
Filename : TURNIT.ASM

;
; Title: TURNIT3.ASM
; Author: F. Ho
; Date: 8th July 1986
; Syntax: ? TURN(expC)
; where: -expC is the character string expression
; to be reversed
; Note: - reverses the order of the string passed
; - can only process a MAX of 60 characters
;
public TURN ; this public statement makes this
; ; routine accessible to the 'public'
;
extrn _PARC:far ; Clipper's character 'getter'
extrn _RETC:far ; Clipper's character 'returner'
;
;
DGROUP GROUP datasg ; Clipper's Data Segment

; the 'public' in the next statement combines the datasg
; to Clipper's DGROUP group
datasg segment public 'DATA'

RETVAL db 60 dup(" ") ; init with 60 spaces
VAL1 dw 00 ; init with 0
VAL2 dw 00 ; init with 0

datasg ends ; end of datasg (in DGROUP)
;
;
_prog segment
assume cs:_prog,ds:DGROUP,es:DGROUP

TURN proc far ; far process

push bp ; preserve return address
mov bp,sp ; move stack pointer

mov ax,1 ; get first para
push ax ; push AX
call _PARC ; call Chara "getter"
add sp,2 ; restore stack
mov VAL1,bx ; get OFFSET address
mov VAL2,ax ; get SEGMENT address

push ds ; preserve DS
push es ; preserve ES
cld ; clear direction flag (L-R)
mov di,offset DGROUP:RETVAL ; get RETVAL's offset
; from DGROUP
mov ax,DGROUP ; get DGROUP segment
mov es,ax ; and place in ES

; in the next three statements, the order that it appears is
; important because the values of SI & AX must first be taken
; from the DATASG extension before assigning the DGROUP segment
; address to DS

mov si,VAL1
mov ax,VAL2
mov ds,ax


xor ax,ax ; zero out AX
mov al,[si] ; move first SI value to AL
cmp al,0 ; if NUL (zero)
jz C3 ; jump to C3

mov cx,3ch ; set CX for max 60 loops
xor bx,bx ; zero-out BX
xor ax,ax ; zero-out AX

A1: mov al,[si] ; move SI value to AL
cmp al,0 ; compare with zero
jz A2 ; if zero, jump to A2:
inc si ; increment SI
inc bx ; increment BX
loop A1 ; loop to A1:

A2: dec si ; decrement SI
mov cx,bx ; move BX to CX
xor ax,ax ; zero-out AX

A3: mov al,[si] ; move SI val to AL
mov es:[di],al ; move AL to DI
dec si ; decrement SI
inc di ; increment DI
loop A3 ; loop

C3: xor ax,ax ; zero-out AX
mov es:[di],al ; add null terminator to end
; of RETVAL

pop es ; restore
pop ds ; restore

pop bp ; restore

mov ax,DGROUP ; get DGROUP address
mov ds,ax ; assign to DS
push ds ; push segment address

mov ax,offset DGROUP:RETVAL ; get RETVAL's offset
push ax ; push offset address
call _RETC ; Clipper's "returner"
pop ax ; restore
pop ds ; restore

ret ; actual ret to caller
TURN endp ; end of process

_prog ends ; end of segment
end ; end of programme
;
;