collapseos/apps/lib/parse.asm
Virgil Dupras 7ca54d179d lib/expr: make EXPR_PARSE "tail" HL
Things are now much simpler.
2019-12-30 19:24:53 -05:00

224 lines
5.1 KiB
NASM

; *** Requirements ***
; lib/util
; *** Code ***
; Parse the hex char at A and extract it's 0-15 numerical value. Put the result
; in A.
;
; On success, the carry flag is reset. On error, it is set.
parseHex:
; First, let's see if we have an easy 0-9 case
add a, 0xc6 ; maps '0'-'9' onto 0xf6-0xff
sub 0xf6 ; maps to 0-9 and carries if not a digit
ret nc
and 0xdf ; converts lowercase to uppercase
add a, 0xe9 ; map 0x11-x017 onto 0xFA - 0xFF
sub 0xfa ; map onto 0-6
ret c
; we have an A-F digit
add a, 10 ; C is clear, map back to 0xA-0xF
ret
; Parse string at (HL) as a decimal value and return value in DE.
; Reads as many digits as it can and stop when:
; 1 - A non-digit character is read
; 2 - The number overflows from 16-bit
; HL is advanced to the character following the last successfully read char.
; Error conditions are:
; 1 - There wasn't at least one character that could be read.
; 2 - Overflow.
; Sets Z on success, unset on error.
parseDecimal:
; First char is special: it has to succeed.
ld a, (hl)
; 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.
add a, 0xff-'9' ; maps '0'-'9' onto 0xf6-0xff
sub 0xff-9 ; maps to 0-9 and carries if not a digit
ret c ; Error. If it's C, it's also going to be NZ
; During this routine, we switch between HL and its shadow. On one side,
; we have HL the string pointer, and on the other side, we have HL the
; numerical result. We also use EXX to preserve BC, saving us a push.
exx ; HL as a result
ld h, 0
ld l, a ; load first digit in without multiplying
ld b, 0 ; We use B to detect overflow
.loop:
exx ; HL as a string pointer
inc hl
ld a, (hl)
exx ; HL as a numerical result
; same as other above
add a, 0xff-'9'
sub 0xff-9
jr c, .end
add hl, hl ; x2
; We do this to detect overflow at each step
rl b
ld d, h
ld e, l ; de is x2
add hl, hl ; x4
rl b
add hl, hl ; x8
rl b
add hl, de ; x10
rl b
ld d, 0
ld e, a
add hl, de
rl b
; Did we oveflow?
xor a
or b
jr z, .loop ; No? continue
; error, NZ already set
exx ; HL is now string pointer, restore BC
; HL points to the char following the last success.
ret
.end:
push hl ; --> lvl 1, result
exx ; HL as a string pointer, restore BC
pop de ; <-- lvl 1, result
cp a ; ensure Z
ret
; Call parseDecimal and then check that HL points to a whitespace or a null.
parseDecimalC:
call parseDecimal
ret nz
ld a, (hl)
or a
ret z ; null? we're happy
jp isWS
; Parse string at (HL) as a hexadecimal value without the "0x" prefix and
; return value in DE.
; HL is advanced to the character following the last successfully read char.
; Sets Z on success.
parseHexadecimal:
ld a, (hl)
call parseHex
jp c, unsetZ ; we need at least one char
push bc
ld de, 0
ld b, 0
.loop:
; we push to B to verify overflow
rl e \ rl d \ rl b
rl e \ rl d \ rl b
rl e \ rl d \ rl b
rl e \ rl d \ rl b
or e
ld e, a
; did we overflow?
ld a, b
or a
jr nz, .end ; overflow, NZ already set
; next char
inc hl
ld a, (hl)
call parseHex
jr nc, .loop
cp a ; ensure Z
.end:
pop bc
ret
; Parse string at (HL) as a binary value (010101) without the "0b" prefix and
; return value in E. D is always zero.
; HL is advanced to the character following the last successfully read char.
; Sets Z on success.
parseBinaryLiteral:
ld de, 0
.loop:
ld a, (hl)
add a, 0xff-'1'
sub 0xff-1
jr c, .end
rl e
add a, e
ld e, a
jp c, unsetZ ; overflow
inc hl
jr .loop
.end:
; HL is properly set
xor a ; ensure Z
ret
; Parses the string at (HL) and returns the 16-bit value in DE. The string
; can be a decimal literal (1234), a hexadecimal literal (0x1234) or a char
; literal ('X').
; HL is advanced to the character following the last successfully read char.
;
; 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.
parseLiteral:
ld de, 0 ; pre-fill
ld a, (hl)
cp 0x27 ; apostrophe
jr z, .char
call isDigit
ret nz
cp '0'
jp nz, parseDecimal
; maybe hex, maybe binary
inc hl
ld a, (hl)
inc hl ; already place it for hex or bin
cp 'x'
jr z, parseHexadecimal
cp 'b'
jr z, parseBinaryLiteral
; nope, just a regular decimal
dec hl \ dec hl
jp parseDecimal
; Parse string at (HL) and, if it is a char literal, sets Z and return
; corresponding value in E. D is always zero.
; HL is advanced to the character following the last successfully read char.
;
; A valid char literal starts with ', ends with ' and has one character in the
; middle. No escape sequence are accepted, but ''' will return the apostrophe
; character.
.char:
inc hl
ld e, (hl) ; our result
inc hl
cp (hl)
jr nz, .charError ; not ending with an apostrophe
; good char, advance HL and return
inc hl
; Z already set
ret
.charError:
; In all error conditions, HL is advanced by 2. Rewind.
dec hl \ dec hl
; NZ already set
ret
; Returns whether A is a literal prefix, that is, a digit or an apostrophe.
isLiteralPrefix:
cp 0x27 ; apostrophe
ret z
; continue to isDigit
; Returns whether A is a digit
isDigit:
cp '0'
jp c, unsetZ
cp '9'+1
jp nc, unsetZ
cp a ; ensure Z
ret