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927d5f2392
I've tweaked nearly every function in this file, so I'll go through them one by one. parseDecimal has been reworked a little so that `a` can be used instead of `b` for checking for overflow. I had originally intended to redo it to work like the old parseDecimal, but I think the current method (once reworked a little) is cleaner and smaller, and should be just as fast. 7 bytes and 27 cycles saved. parseHexadecimal has been changed to load hex digits into `b` `d` `c` `e` from the right (so all the digits move along to the left so the new digit can be inserted on the right), and then only at the end is any shifting done, using the faster `add a, a` to do left shifts. 9 bytes saved and 78 cycles saved inside the loop, and then 49 cycles added after the loop. parseBinaryLiteral had a few instructions moved around, saving two bytes and 5 cycles inside the loop, and a further 15 cycles saved on error. parseLiteral has been reworked slightly, the isDigit call has been replaced with an inline parseDecimalDigit, saving a byte and around 20-30 cycles, with around 16 more cycles saved if the number is a decimal. The .char routine has been reduced by a byte, and 6 cycles saved on success, but 5 cycles added on error. isDigit has been reduced by 4 bytes and 10 cycles on success, with a few more cycles saved on fail (hard to estimate due to branching).
239 lines
6.2 KiB
NASM
239 lines
6.2 KiB
NASM
; *** Requirements ***
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; lib/util
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; *** Code ***
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; Parse the hex char at A and extract it's 0-15 numerical value. Put the result
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; in A.
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;
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; On success, the carry flag is reset. On error, it is set.
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parseHex:
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; First, let's see if we have an easy 0-9 case
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add a, 0xc6 ; maps '0'-'9' onto 0xf6-0xff
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sub 0xf6 ; maps to 0-9 and carries if not a digit
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ret nc
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and 0xdf ; converts lowercase to uppercase
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add a, 0xe9 ; map 0x11-x017 onto 0xFA - 0xFF
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sub 0xfa ; map onto 0-6
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ret c
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; we have an A-F digit
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add a, 10 ; C is clear, map back to 0xA-0xF
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ret
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; Parse string at (HL) as a decimal value and return value in DE.
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; Reads as many digits as it can and stop when:
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; 1 - A non-digit character is read
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; 2 - The number overflows from 16-bit
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; HL is advanced to the character following the last successfully read char.
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; Error conditions are:
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; 1 - There wasn't at least one character that could be read.
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; 2 - Overflow.
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; Sets Z on success, unset on error.
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parseDecimal:
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; First char is special: it has to succeed.
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ld a, (hl)
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; Parse the decimal char at A and extract it's 0-9 numerical value. Put the
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; result in A.
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; On success, the carry flag is reset. On error, it is set.
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add a, 0xff-'9' ; maps '0'-'9' onto 0xf6-0xff
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sub 0xff-9 ; maps to 0-9 and carries if not a digit
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ret c ; Error. If it's C, it's also going to be NZ
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; During this routine, we switch between HL and its shadow. On one side,
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; we have HL the string pointer, and on the other side, we have HL the
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; numerical result. We also use EXX to preserve BC, saving us a push.
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parseDecimalSkip: ; enter here to skip parsing the first digit
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exx ; HL as a result
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ld h, 0
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ld l, a ; load first digit in without multiplying
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.loop:
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exx ; HL as a string pointer
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inc hl
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ld a, (hl)
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exx ; HL as a numerical result
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; same as other above
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add a, 0xff-'9'
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sub 0xff-9
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jr c, .end
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ld b, a ; we can now use a for overflow checking
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add hl, hl ; x2
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sbc a, a ; a=0 if no overflow, a=0xFF otherwise
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ld d, h
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ld e, l ; de is x2
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add hl, hl ; x4
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rla
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add hl, hl ; x8
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rla
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add hl, de ; x10
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rla
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ld d, a ; a is zero unless there's an overflow
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ld e, b
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add hl, de
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adc a, a ; same as rla except affects Z
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; Did we oveflow?
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jr z, .loop ; No? continue
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; error, NZ already set
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exx ; HL is now string pointer, restore BC
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; HL points to the char following the last success.
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ret
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.end:
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push hl ; --> lvl 1, result
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exx ; HL as a string pointer, restore BC
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pop de ; <-- lvl 1, result
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cp a ; ensure Z
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ret
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; Call parseDecimal and then check that HL points to a whitespace or a null.
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parseDecimalC:
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call parseDecimal
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ret nz
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ld a, (hl)
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or a
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ret z ; null? we're happy
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jp isWS
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; Parse string at (HL) as a hexadecimal value without the "0x" prefix and
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; return value in DE.
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; HL is advanced to the character following the last successfully read char.
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; Sets Z on success.
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parseHexadecimal:
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ld a, (hl)
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call parseHex ; before "ret c" is "sub 0xfa" in parseHex
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; so carry implies not zero
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ret c ; we need at least one char
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push bc
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ld de, 0
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ld b, d
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ld c, d
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; The idea here is that the 4 hex digits of the result can be represented "bdce",
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; where each register holds a single digit. Then the result is simply
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; e = (c << 4) | e, d = (b << 4) | d
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; However, the actual string may be of any length, so when loading in the most
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; significant digit, we don't know which digit of the result it actually represents
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; To solve this, after a digit is loaded into a (and is checked for validity),
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; all digits are moved along, with e taking the latest digit.
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.loop:
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dec b
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inc b ; b should be 0, else we've overflowed
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jr nz, .end ; Z already unset if overflow
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ld b, d
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ld d, c
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ld c, e
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ld e, a
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inc hl
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ld a, (hl)
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call parseHex
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jr nc, .loop
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ld a, b
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add a, a \ add a, a \ add a, a \ add a, a
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or d
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ld d, a
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ld a, c
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add a, a \ add a, a \ add a, a \ add a, a
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or e
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ld e, a
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xor a ; ensure z
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.end:
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pop bc
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ret
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; Parse string at (HL) as a binary value (010101) without the "0b" prefix and
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; return value in E. D is always zero.
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; HL is advanced to the character following the last successfully read char.
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; Sets Z on success.
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parseBinaryLiteral:
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ld de, 0
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.loop:
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ld a, (hl)
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add a, 0xff-'1'
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sub 0xff-1
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jr c, .end
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rlc e ; sets carry if overflow, and affects Z
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ret c ; Z unset if carry set, since bit 0 of e must be set
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add a, e
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ld e, a
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inc hl
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jr .loop
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.end:
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; HL is properly set
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xor a ; ensure Z
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ret
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; Parses the string at (HL) and returns the 16-bit value in DE. The string
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; can be a decimal literal (1234), a hexadecimal literal (0x1234) or a char
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; literal ('X').
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; HL is advanced to the character following the last successfully read char.
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;
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; As soon as the number doesn't fit 16-bit any more, parsing stops and the
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; number is invalid. If the number is valid, Z is set, otherwise, unset.
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parseLiteral:
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ld de, 0 ; pre-fill
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ld a, (hl)
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cp 0x27 ; apostrophe
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jr z, .char
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; inline parseDecimalDigit
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add a, 0xc6 ; maps '0'-'9' onto 0xf6-0xff
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sub 0xf6 ; maps to 0-9 and carries if not a digit
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ret c
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; a already parsed so skip first few instructions of parseDecimal
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jp nz, parseDecimalSkip
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; maybe hex, maybe binary
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inc hl
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ld a, (hl)
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inc hl ; already place it for hex or bin
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cp 'x'
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jr z, parseHexadecimal
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cp 'b'
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jr z, parseBinaryLiteral
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; nope, just a regular decimal
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dec hl \ dec hl
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jp parseDecimal
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; Parse string at (HL) and, if it is a char literal, sets Z and return
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; corresponding value in E. D is always zero.
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; HL is advanced to the character following the last successfully read char.
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;
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; A valid char literal starts with ', ends with ' and has one character in the
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; middle. No escape sequence are accepted, but ''' will return the apostrophe
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; character.
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.char:
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inc hl
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ld e, (hl) ; our result
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inc hl
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cp (hl)
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; advance HL and return if good char
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inc hl
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ret z
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; Z unset and there's an error
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; In all error conditions, HL is advanced by 3. Rewind.
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dec hl \ dec hl \ dec hl
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; NZ already set
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ret
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; Returns whether A is a literal prefix, that is, a digit or an apostrophe.
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isLiteralPrefix:
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cp 0x27 ; apostrophe
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ret z
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; continue to isDigit
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; Returns whether A is a digit
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isDigit:
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cp '0' ; carry implies not zero for cp
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ret c
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cp '9' ; zero unset for a > '9', but set for a='9'
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ret nc
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cp a ; ensure Z
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ret
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