mirror of
https://github.com/hsoft/collapseos.git
synced 2024-11-30 20:48:06 +11:00
60 lines
1.2 KiB
NASM
60 lines
1.2 KiB
NASM
; Parse the decimal char at A and extract it's 0-9 numerical value. Put the
|
|
; result in A.
|
|
;
|
|
; On success, the carry flag is reset. On error, it is set.
|
|
parseDecimal:
|
|
; First, let's see if we have an easy 0-9 case
|
|
cp '0'
|
|
ret c ; if < '0', we have a problem
|
|
cp '9'+1
|
|
; We are in the 0-9 range
|
|
sub a, '0' ; C is clear
|
|
ret
|
|
|
|
; Parses the string at (HL) and returns the 16-bit value in IX.
|
|
; As soon as the number doesn't fit 16-bit any more, parsing stops and the
|
|
; number is invalid. If the number is valid, Z is set, otherwise, unset.
|
|
parseNumber:
|
|
push hl
|
|
push de
|
|
push bc
|
|
|
|
ld ix, 0
|
|
.loop:
|
|
ld a, (hl)
|
|
cp 0
|
|
jr z, .end ; success!
|
|
call parseDecimal
|
|
jr c, .error
|
|
|
|
; Now, let's add A to IX. First, multiply by 10.
|
|
ld d, ixh ; we need a copy of the initial copy for later
|
|
ld e, ixl
|
|
add ix, ix ; x2
|
|
add ix, ix ; x4
|
|
add ix, ix ; x8
|
|
add ix, de ; x9
|
|
add ix, de ; x10
|
|
add a, ixl
|
|
jr nc, .nocarry
|
|
inc ixh
|
|
.nocarry:
|
|
ld ixl, a
|
|
|
|
; We didn't bother checking for the C flag at each step because we
|
|
; check for overflow afterwards. If ixh < d, we overflowed
|
|
ld a, ixh
|
|
cp d
|
|
jr c, .error ; carry is set? overflow
|
|
|
|
inc hl
|
|
jr .loop
|
|
|
|
.error:
|
|
call JUMP_UNSETZ
|
|
.end:
|
|
pop bc
|
|
pop de
|
|
pop hl
|
|
ret
|