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Fixed more errors, clearer choice of constants

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Clanmaster21 2019-10-21 02:13:21 +01:00 committed by GitHub
parent ab4fca334d
commit edbd775642
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1 changed files with 8 additions and 13 deletions
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21
apps/lib/parse.asm
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@ -9,28 +9,23 @@
; On success, the carry flag is reset. On error, it is set. ; On success, the carry flag is reset. On error, it is set.
; Also, zero flag set if '0' ; Also, zero flag set if '0'
; parseDecimalDigit has been replaced with the following code inline: ; parseDecimalDigit has been replaced with the following code inline:
; add a, 0xc6 ; Maps '0'-'9' onto 0xf6-0xff ; add a, 0xff-'9' ; maps '0'-'9' onto 0xf6-0xff
; sub 0xf6 ; Anything but 0xf6-0xff carries ; sub 0xff-9 ; maps to 0-9 and carries if not a digit
; Maps 0xf6-0xff onto 0-9
; Parse string at (HL) as a decimal value and return value in IX under the ; Parse string at (HL) as a decimal value and return value in IX under the
; same conditions as parseLiteral. ; same conditions as parseLiteral.
; Sets Z on success, unset on error. ; Sets Z on success, unset on error.
; 61 bytes
; 107 cycles overhead + up to 73 cycles if length >= 5
; 136 cycles in loop
; first digit is skipped in overhead
parseDecimal: parseDecimal:
push hl push hl
ld a, (hl) ld a, (hl)
add a, 0xc6 ; converts '0'-'9' to 0-9 add a, 0xff-'9' ; maps '0'-'9' onto 0xf6-0xff
sub 0xf6 ; carries if out of range sub 0xff-9 ; maps to 0-9 and carries if not a digit
exx ; preserve bc, hl, de exx ; preserve bc, hl, de
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, 4 ; 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, .error
.loop: .loop:
@ -39,8 +34,8 @@ parseDecimal:
ld a, (hl) ld a, (hl)
exx exx
add a, 0xc6 ; converts '0'-'9' to 0-9 add a, 0xff-'9' ; maps '0'-'9' onto 0xf6-0xff
sub 0xf6 ; carries if out of range sub 0xff-9 ; maps to 0-9 and carries if not a digit
jr c, .error jr c, .error
add hl, hl ; x2 add hl, hl ; x2
@ -68,7 +63,7 @@ parseDecimal:
inc hl inc hl
ld a, (hl) ld a, (hl)
exx exx
add a, 0xd0 add a, 0xd0 ; the next line expects a null to be mapped to 0xd0
.error: .error:
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