collapseos/apps/lib/parse.asm

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; *** Requirements ***
; unsetZ
;
; *** Code ***
; 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.
parseDecimalDigit:
; First, let's see if we have an easy 0-9 case
cp '0'
ret c ; if < '0', we have a problem
sub '0' ; our value now is valid if it's < 10
cp 10 ; on success, C is set, which is the opposite
; of what we want
ccf ; invert C flag
ret
; Parse string at (HL) as a decimal value and return value in IX under the
; same conditions as parseLiteral.
; Sets Z on success, unset on error.
parseDecimal:
push hl
push de
ld ix, 0
.loop:
ld a, (hl)
or a
jr z, .end ; success!
call parseDecimalDigit
jr c, .error
; Now, let's add A to IX. First, multiply by 10.
push ix \ pop de
add ix, ix ; x2
jr c, .error
add ix, ix ; x4
jr c, .error
add ix, ix ; x8
jr c, .error
add ix, de ; x9
jr c, .error
add ix, de ; x10
jr c, .error
ld d, 0
ld e, a
add ix, de
jr c, .error
inc hl
jr .loop
cp a ; ensure Z
jr .end
.error:
call unsetZ
.end:
pop de
pop hl
ret