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forth: Word-ify number parsing
This commit is contained in:
Virgil Dupras
parent
707f1dbae1
commit
4212d5161f
@ -339,29 +339,13 @@ COMPILE:
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.db 0b10 ; UNWORD
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.maybeNum:
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.dw compiledWord
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.dw .parseNum
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.dw PARSE
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.dw LITN
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.dw R2P ; exit COMPILE
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.dw DROP
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.dw EXIT
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.db 0b10 ; UNWORD
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.parseNum:
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.dw nativeWord
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pop hl ; string addr
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push hl ; --> lvl 1. save string addr
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call parseLiteral
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pop hl ; <-- lvl 1
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jr nz, .undef
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; a valid number in DE!
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push de
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jp next
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.undef:
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call printstr
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jp abortUnknownWord
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.db ":"
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.fill 6
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.dw COMPILE
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@ -562,9 +546,55 @@ WORD:
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push hl
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jp next
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.db "(parsed"
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.dw WORD
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.db 0
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PARSED:
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.dw nativeWord
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pop hl
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call chkPS
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; temporary: run parseCharLit in here until it's implemented in Forth
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; core.fs needs char literal parsing.
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call parseCharLit
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jr z, .success
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call parseDecimal
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jr z, .success
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; error
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ld de, 0
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push de ; dummy
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push de ; flag
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jp next
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.success:
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push de
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ld de, 1 ; flag
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push de
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jp next
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.db "(parse)"
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.dw WORD
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.db 0
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PARSE:
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.dw compiledWord
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.dw PARSED
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.dw CSKIP
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.dw .error
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; success, stack is already good, we can exit
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.dw EXIT
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.db 0b10 ; UNWORD
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.error:
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.dw compiledWord
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.dw LIT
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.db "unknown word", 0
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.dw PRINT
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.dw ABORT
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.db "CREATE"
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.fill 1
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.dw WORD
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.dw PARSE
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.db 0
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CREATE:
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.dw nativeWord
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@ -151,6 +151,31 @@ wait until another line is entered.
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KEY input, however, is direct. Regardless of the input buffer's state, KEY will
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return the next typed key.
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PARSING AND BOOTSTRAP: Parsing number literal is a very "core" activity of
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Forth, and therefore generally seen as having to be implemented in native code.
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However, Collapse OS' Forth supports many kinds of literals: decimal, hex, char,
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binary. This incurs a significant complexity penalty.
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What if we could implement those parsing routines in Forth? "But it's a core
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routine!" you say. Yes, but here's the deal: at its native core, only decimal
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parsing is supported. It lives in the "(parsed)" word. The interpreter's main
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loop is initially set to simply call that word.
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However, in core.fs, "(parsex)", "(parsec)" and "(parseb)" are implemented, in
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Forth, then "(parse)", which goes through them all is defined. Then, "(parsef)",
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which is the variable in which the interpreter's word pointer is set, is
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updated to that new "(parse)" word.
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This way, we have a full-featured (and extensible) parsing with a tiny native
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core.
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(parse) a -- n Parses string at a as a number and push the result
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in n as well as whether parsing was a success in f
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(false = failure, true = success)
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(parse.) a -- n f Sub-parsing words. They all have the same signature.
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Parses string at a as a number and push the result
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in n as well as whether parsing was a success in f
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(0 = failure, 1 = success)
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(print) a -- Print string at addr a.
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. n -- Print n in its decimal form
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.X n -- Print n in its hexadecimal form. In hex, numbers
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@ -96,32 +96,24 @@ forthRdLineNoOk:
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.db 0b10 ; UNWORD
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INTERPRET:
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.dw nativeWord
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pop hl ; from WORD
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ld a, (hl) ; special case: empty
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or a
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jp z, next
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call find
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jr nz, .maybeNum
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; regular word
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push de
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jp EXECUTE+2
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.dw compiledWord
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.dw FIND_
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.dw CSKIP
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.dw .maybeNum
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; It's a word, execute it
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.dw EXECUTE
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.dw EXIT
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.maybeNum:
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push hl ; --> lvl 1. save string addr
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call parseLiteral
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pop hl ; <-- lvl 1
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jr nz, .undef
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; a valid number in DE!
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push de
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jp next
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.undef:
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call printstr
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jp abortUnknownWord
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.dw compiledWord
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.dw PARSE
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.dw R2P ; exit INTERPRET
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.dw DROP
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.dw EXIT
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.db 0b10 ; UNWORD
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MAINLOOP:
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.dw compiledWord
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.dw WORD
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.dw INTERPRET
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.dw INP
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.dw FETCH
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@ -115,25 +115,6 @@ multDEBC:
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jr nz, .loop
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ret
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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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@ -156,7 +137,6 @@ parseDecimal:
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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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@ -201,127 +181,21 @@ parseDecimalSkip: ; enter here to skip parsing the first digit
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cp a ; ensure Z
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ret
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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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parseCharLit:
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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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ret nz
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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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ld d, 0 ; preset
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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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; In all error conditions, HL is advanced by 2. Rewind.
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dec hl \ dec hl
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; NZ already set
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ret
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