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kermcsum.asm
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Assembly Source File
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1990-07-08
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1KB
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48 lines
; Fil: KERMCSUM.ASM
; Av: Kristoffer Eriksson, "SKE" <5357>, 1987.
;
;-Ver--/-Datum----/-Sign-/-Kommentar----------------------------------
; 1.00 / 87-08-15 / SKE / KERMCSUM
;
; Kontrollsummarutin till Bo Kullmars Kermit-program K.
;* Summera str{ng f|r Kermit-kontrollsumma.
;* In: DE = VAROOT(Str{ng$)
;* Ut: L = Summa, bittar 5-0,
;* H = Summa, bittar 13-6.
Csum: ex de,hl
inc hl
inc hl
ld e,(hl) ; DE <- Str{ngens adress.
inc hl
ld d,(hl)
inc hl
ld c,(hl) ; BC <- Str{ngens l{ngd.
inc hl
ld b,(hl)
ld hl,0 ; HL <- Startsumma = 0.
Loop: ld a,c ; Slut?
or b
jr z CEnd
ld a,(de) ; Summera.
add l
ld l,a
ld a,0
adc h
ld h,a
dec bc
inc de
jr Loop
CEnd: ld a,l
rlc a
rl h
rlc a
rl h ; H <- bit 13-6.
ld a,l
and 63
ld l,a ; L <- bit 5-0.
ret