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Renamed .error, removed trailing whitespace, more verbose comments.

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Clanmaster21 2019-10-21 15:30:28 +01:00 committed by GitHub
parent 8093bef9cb
commit 7d43f7a760
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1 changed files with 11 additions and 8 deletions
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19
apps/lib/parse.asm
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@ -26,17 +26,19 @@ parseDecimal:
ld h, 0 ld h, 0
ld l, a ; load first digit in without multiplying ld l, a ; load first digit in without multiplying
ld b, 3 ; Carries can only occur for decimals >=5 in length ld b, 3 ; Carries can only occur for decimals >=5 in length
jr c, .error jr c, .end
.loop: .loop:
exx exx
inc hl inc hl
ld a, (hl) ld a, (hl)
exx exx
; inline parseDecimalDigit
add a, 0xff-'9' ; maps '0'-'9' onto 0xf6-0xff add a, 0xff-'9' ; maps '0'-'9' onto 0xf6-0xff
sub 0xff-9 ; maps to 0-9 and carries if not a digit sub 0xff-9 ; maps to 0-9 and carries if not a digit
jr c, .error
jr c, .end
add hl, hl ; x2 add hl, hl ; x2
ld d, h ld d, h
@ -47,13 +49,13 @@ parseDecimal:
ld d, 0 ld d, 0
ld e, a ld e, a
add hl, de add hl, de
jr c, .error ; if hl was 0x1999, it may carry here jr c, .end ; if hl was 0x1999, it may carry here
djnz .loop djnz .loop
inc b ; so loop only executes once more inc b ; so loop only executes once more
; only numbers >0x1999 can carry when multiplied by 10. ; only numbers >0x1999 can carry when multiplied by 10.
ld de, 0xE666 ld de, 0xE666
ex de, hl ex de, hl
add hl, de add hl, de
ex de, hl ex de, hl
@ -64,11 +66,12 @@ parseDecimal:
ld a, (hl) ld a, (hl)
exx exx
add a, 0xd0 ; the next line expects a null to be mapped to 0xd0 add a, 0xd0 ; the next line expects a null to be mapped to 0xd0
.error: .end:
; Because of the add and sub in parseDecimalDigit, null is mapped
; to 0x00+(0xff-'9')-(0xff-9)=-0x30=0xd0
sub 0xd0 ; if a is null, set Z sub 0xd0 ; if a is null, set Z
; a is checked for null before any errors ; a is checked for null before any errors
.end:
push hl \ pop ix push hl \ pop ix
exx ; restore original de and bc exx ; restore original de and bc
pop hl pop hl
ret ret