mirror of https://github.com/hsoft/collapseos.git
lib/parse: make parseLiteral a little tighter
Sub-parsers are seldom used by themselves, except for parseDecimal. I'm tightening the code of this unit for two reasons: 1. Optimization 2. Upcoming API change where HL won't be preserved anymore, but will point to char following the last parse char. This will allow us to simplify lib/expr.
This commit is contained in:
Virgil Dupras
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15628da7de
commit
d0f031939f
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@ -74,6 +74,8 @@ There are decimal, hexadecimal and binary literals. A "straight" number is
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parsed as a decimal. Hexadecimal literals must be prefixed with `0x` (`0xf4`).
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Binary must be prefixed with `0b` (`0b01100110`).
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A decimal literal cannot start with `0`, with the exception of the `0` literal.
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Decimals and hexadecimal are "flexible". Whether they're written in a byte or
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a word, you don't need to prefix them with zeroes. Watch out for overflow,
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however.
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@ -140,15 +140,11 @@ parseDecimal:
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pop hl ; <-- lvl 1, orig
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jp unsetZ
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; Parse string at (HL) as a hexadecimal value and return value in DE under the
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; same conditions as parseLiteral.
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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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; Sets Z on success.
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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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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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@ -182,29 +178,12 @@ parseHexadecimal:
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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 E.
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; D is always zero.
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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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; 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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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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@ -237,49 +216,6 @@ parseBinaryLiteral:
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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 E. D is always zero.
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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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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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pop hl
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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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@ -287,11 +223,57 @@ parseCharLiteral:
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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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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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cp '0'
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jr z, .hexOrBin
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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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;
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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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push hl
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inc hl
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inc hl
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cp (hl)
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jr nz, .charEnd ; 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, .charEnd ; string has to end there
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; Valid char, good
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dec hl
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dec hl
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ld e, (hl)
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cp a ; ensure Z
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.charEnd:
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pop hl
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ret
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.hexOrBin:
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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, .hex
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cp 'b'
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jr z, .bin
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; special case: single '0'. set Z if we hit have null terminating.
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or a
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.hexOrBinEnd:
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dec hl \ dec hl ; replace HL
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ret ; Z already set
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.hex:
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call parseHexadecimal
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jr .hexOrBinEnd
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.bin:
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call parseBinaryLiteral
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jr .hexOrBinEnd
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