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collapseos/apps/lib/parse.asm
Virgil Dupras 8d46895dd3 lib/parse: decimal ending with a whitespace are now valid
Also, make empty strings be parsed as invalid by parseDecimal.
2019-11-13 22:10:06 -05:00

83 lines
2.1 KiB
NASM

; *** 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.
; Also, zero flag set if '0'
; parseDecimalDigit has been replaced with the following code inline:
; add a, 0xff-'9' ; maps '0'-'9' onto 0xf6-0xff
; sub 0xff-9 ; maps to 0-9 and carries if not a digit
; 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.
; To parse successfully, all characters following HL must be digits and those
; digits must form a number that fits in 16 bits. To end the number, both \0
; and whitespaces (0x20 and 0x09) are accepted. There must be at least one
; digit in the string.
parseDecimal:
push hl
ld a, (hl)
add a, 0xff-'9' ; maps '0'-'9' onto 0xf6-0xff
sub 0xff-9 ; maps to 0-9 and carries if not a digit
jr c, .error ; not a digit on first char? error
exx ; preserve bc, hl, de
ld h, 0
ld l, a ; load first digit in without multiplying
ld b, 3 ; Carries can only occur for decimals >=5 in length
.loop:
exx
inc hl
ld a, (hl)
exx
; inline parseDecimalDigit
add a, 0xff-'9' ; maps '0'-'9' onto 0xf6-0xff
sub 0xff-9 ; maps to 0-9 and carries if not a digit
jr c, .end
add hl, hl ; x2
ld d, h
ld e, l ; de is x2
add hl, hl ; x4
add hl, hl ; x8
add hl, de ; x10
ld d, 0
ld e, a
add hl, de
jr c, .end ; if hl was 0x1999, it may carry here
djnz .loop
inc b ; so loop only executes once more
; only numbers >0x1999 can carry when multiplied by 10.
ld de, 0xE666
ex de, hl
add hl, de
ex de, hl
jr nc, .loop ; if it doesn't carry, it's small enough
exx
inc hl
ld a, (hl)
exx
add a, 0xd0 ; the next line expects a null to be mapped to 0xd0
.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
; a is checked for null before any errors
push hl \ pop ix
exx ; restore original de and bc
pop hl
ret z
; A is not 0? Ok, but if it's a space, we're happy too.
jp isSep
.error:
pop hl
jp unsetZ