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304 lines
6.4 KiB
NASM
304 lines
6.4 KiB
NASM
; *** 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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; Parses 2 characters of the string pointed to by HL and returns the numerical
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; value in A. If the second character is a "special" character (<0x21) we don't
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; error out: the result will be the one from the first char only.
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; HL is set to point to the last char of the pair.
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;
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; On success, the carry flag is reset. On error, it is set.
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parseHexPair:
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push bc
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ld a, (hl)
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call parseHex
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jr c, .end ; error? goto end, keeping the C flag on
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rla \ rla \ rla \ rla ; let's push this in MSB
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ld b, a
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inc hl
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ld a, (hl)
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cp 0x21
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jr c, .single ; special char? single digit
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call parseHex
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jr c, .end ; error?
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or b ; join left-shifted + new. we're done!
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; C flag was set on parseHex and is necessarily clear at this point
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jr .end
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.single:
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; If we have a single digit, our result is already stored in B, but
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; we have to right-shift it back.
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ld a, b
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and 0xf0
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rra \ rra \ rra \ rra
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dec hl
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.end:
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pop bc
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ret
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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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;
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; On success, the carry flag is reset. On error, it is set.
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; Also, zero flag set if '0'
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; parseDecimalDigit has been replaced with the following code inline:
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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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; Parse string at (HL) as a decimal value and return value in IX under the
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; same conditions as parseLiteral.
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; Sets Z on success, unset on error.
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; To parse successfully, all characters following HL must be digits and those
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; digits must form a number that fits in 16 bits. To end the number, both \0
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; and whitespaces (0x20 and 0x09) are accepted. There must be at least one
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; digit in the string.
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parseDecimal:
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push hl
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ld a, (hl)
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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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jr c, .error ; not a digit on first char? error
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exx ; preserve bc, hl, de
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ld h, 0
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ld l, a ; load first digit in without multiplying
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ld b, 3 ; Carries can only occur for decimals >=5 in length
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.loop:
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exx
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inc hl
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ld a, (hl)
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exx
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; inline parseDecimalDigit
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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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jr c, .end
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add hl, hl ; x2
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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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add hl, hl ; x8
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add hl, de ; x10
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ld d, 0
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ld e, a
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add hl, de
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jr c, .end ; if hl was 0x1999, it may carry here
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djnz .loop
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inc b ; so loop only executes once more
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; only numbers >0x1999 can carry when multiplied by 10.
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ld de, 0xE666
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ex de, hl
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add hl, de
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ex de, hl
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jr nc, .loop ; if it doesn't carry, it's small enough
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exx
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inc hl
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ld a, (hl)
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exx
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add a, 0xd0 ; the next line expects a null to be mapped to 0xd0
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.end:
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; Because of the add and sub in parseDecimalDigit, null is mapped
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; to 0x00+(0xff-'9')-(0xff-9)=-0x30=0xd0
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sub 0xd0 ; if a is null, set Z
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; a is checked for null before any errors
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push hl \ pop ix
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exx ; restore original de and bc
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pop hl
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ret z
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; A is not 0? Ok, but if it's a space, we're happy too.
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jp isWS
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.error:
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pop hl
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jp unsetZ
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; Parse string at (HL) as a hexadecimal value and return value in IX under the
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; same conditions as parseLiteral.
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parseHexadecimal:
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call hasHexPrefix
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ret nz
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push hl
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push de
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ld d, 0
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inc hl ; get rid of "0x"
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inc hl
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call strlen
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cp 3
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jr c, .single
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cp 4
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jr c, .doubleShort ; 0x123
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cp 5
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jr c, .double ; 0x1234
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; too long, error
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jr .error
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.double:
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call parseHexPair
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jr c, .error
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inc hl ; now HL is on first char of next pair
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ld d, a
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jr .single
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.doubleShort:
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ld a, (hl)
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call parseHex
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jr c, .error
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inc hl ; now HL is on first char of next pair
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ld d, a
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.single:
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call parseHexPair
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jr c, .error
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ld e, a
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cp a ; ensure Z
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jr .end
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.error:
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call unsetZ
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.end:
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push de \ pop ix
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pop de
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pop hl
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ret
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; Sets Z if (HL) has a '0x' prefix.
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hasHexPrefix:
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ld a, (hl)
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cp '0'
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ret nz
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push hl
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inc hl
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ld a, (hl)
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cp 'x'
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pop hl
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ret
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; Parse string at (HL) as a binary value (0b010101) and return value in IX.
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; High IX byte is always clear.
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; Sets Z on success.
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parseBinaryLiteral:
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call hasBinPrefix
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ret nz
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push bc
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push hl
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push de
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ld d, 0
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inc hl ; get rid of "0b"
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inc hl
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call strlen
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or a
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jr z, .error ; empty, error
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cp 9
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jr nc, .error ; >= 9, too long
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; We have a string of 8 or less chars. What we'll do is that for each
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; char, we rotate left and set the LSB according to whether we have '0'
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; or '1'. Error out on anything else. C is our stored result.
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ld b, a ; we loop for "strlen" times
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ld c, 0 ; our stored result
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.loop:
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rlc c
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ld a, (hl)
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inc hl
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cp '0'
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jr z, .nobit ; no bit to set
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cp '1'
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jr nz, .error ; not 0 or 1
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; We have a bit to set
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inc c
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.nobit:
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djnz .loop
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ld e, c
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cp a ; ensure Z
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jr .end
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.error:
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call unsetZ
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.end:
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push de \ pop ix
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pop de
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pop hl
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pop bc
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ret
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; Sets Z if (HL) has a '0b' prefix.
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hasBinPrefix:
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ld a, (hl)
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cp '0'
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ret nz
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push hl
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inc hl
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ld a, (hl)
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cp 'b'
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pop hl
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ret
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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 IX. High IX byte is always clear.
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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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parseCharLiteral:
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ld a, 0x27 ; apostrophe (') char
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cp (hl)
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ret nz
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push hl
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push de
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inc hl
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inc hl
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cp (hl)
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jr nz, .end ; not ending with an apostrophe
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inc hl
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ld a, (hl)
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or a ; cp 0
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jr nz, .end ; string has to end there
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; Valid char, good
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ld d, a ; A is zero, take advantage of that
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dec hl
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dec hl
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ld a, (hl)
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ld e, a
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cp a ; ensure Z
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.end:
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push de \ pop ix
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pop de
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pop hl
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ret
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; Parses the string at (HL) and returns the 16-bit value in IX. 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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;
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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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call parseCharLiteral
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ret z
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call parseHexadecimal
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ret z
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call parseBinaryLiteral
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ret z
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jp parseDecimal
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