Category : Assembly Language Source Code
Archive   : ASM-SUBR.ZIP
Filename : DECHALF

;-------------------------dechalf routine begins--------------------------+
; from BLUEBOOK OF ASSEMBLY ROUTINES FOR IBM PC & XT.
; page : 101
;
; NAME DECHALF
;
; ROUTINE FOR Halving A Temporary Decimal Floating Point Number
;
; FUNCTION: This routine divides a temporary decimal floating point number
; by two.
;
; INPUT: Upon input DI points to a temporary decimal floating point number.
;
; OUTPUT: Upon exit the number has been divided by two.
;
; REGISTERS USED: AX, CX and DI are modified.
;
; SEGMENTS REFERENCED: The data segment contains a temporary decimal
; floating point number.
;
; ROUTINES CALLED: None
;
; SPECIAL NOTES: This is a NEAR routine called by FPOUT.
;
; ROUTINE TO DIVIDE TEMPORARY FP DECIMAL NUMBER BY 2 - RESULT NOT HALVED.
;
dechalf proc near
;
; first shift up one digit
mov cx,25 ; for a count of 25
mov al,0 ; zero previous byte
;
dechalf1:
xchg al,[di] ; exchange with current digit
inc di ; point to next digit
loop dechalf1
;
dec decexp ; decrement decimal digit
;
; now divide by two
mov cx,25 ; for a count of 25
mov ah,0 ; clear
;
dechalf2:
push cx ; save count
dec di ; point to next digit
mov al,[di] ; get the digit
mov cl,2 ; divisor of 2
aad ; adjust for division
div cl ; divide
mov [di],al ; put back
pop cx ; restore count
loop dechalf2
;
ret ; return
;
dechalf endp
;-------------------------dechalf routine ends---------------------------+