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zasm: add support for numerical constants
This commit is contained in:
Virgil Dupras
parent
3fe5eb3e60
commit
7996a9997a
@ -33,6 +33,64 @@ rlaX:
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djnz .loop
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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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parseDecimal:
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; First, let's see if we have an easy 0-9 case
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cp '0'
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ret c ; if < '0', we have a problem
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cp '9'+1
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; We are in the 0-9 range
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sub a, '0' ; C is clear
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ret
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; Parses the string at (HL) and returns the 16-bit value in IX.
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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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parseNumber:
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push hl
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push de
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ld ix, 0
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.loop:
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ld a, (hl)
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cp 0
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jr z, .end ; success!
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call parseDecimal
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jr c, .error
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; Now, let's add A to IX. First, multiply by 10.
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ld d, ixh ; we need a copy of the initial copy for later
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ld e, ixl
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add ix, ix ; x2
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add ix, ix ; x4
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add ix, ix ; x8
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add ix, de ; x9
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add ix, de ; x10
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add a, ixl
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jr nc, .nocarry
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inc ixh
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.nocarry:
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ld ixl, a
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; We didn't bother checking for the C flag at each step because we
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; check for overflow afterwards. If ixh < d, we overflowed
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ld a, ixh
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cp d
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jr c, .error ; carry is set? overflow
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inc hl
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jr .loop
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.error:
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call unsetZ
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.end:
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pop de
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pop hl
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ret
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; Sets Z is A is ';', CR, LF, or null.
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isLineEnd:
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cp ';'
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@ -112,14 +170,24 @@ toWord:
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; HL is advanced to the next word. Z is set if there's a next word.
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readArg:
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push de
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ld de, tmpVal
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ld de, tmpBuf
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call readWord
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push hl
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ld hl, tmpVal
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ld hl, tmpBuf
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call parseArg
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pop hl
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pop de
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ld (de), a
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; When A is a number, IX is set with the value of that number. Because
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; We don't use the space allocated to store those numbers in any other
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; occasion, we store IX there unconditonally, LSB first.
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inc de
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ld a, ixl
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ld (de), a
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inc de
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ld a, ixh
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ld (de), a
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call toWord
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ret
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@ -168,6 +236,9 @@ strlen:
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; Return value 0xff holds a special meaning: arg is not empty, but doesn't match
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; any argspec (A == 0 means arg is empty). A return value of 0xff means an
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; error.
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;
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; If the parsed argument is a number constant, 'N' is returned and IX contains
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; the value of that constant.
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parseArg:
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call strlen
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cp 0
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@ -190,8 +261,14 @@ parseArg:
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ld a, 5
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call JUMP_ADDDE
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djnz .loop1
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; exhausted? we have a problem os specifying a wrong argspec. This is
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; an internal consistency error.
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; We exhausted the argspecs. Let's see if it's a number
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call parseNumber
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jr nz, .notanumber
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; Alright, we have a parsed number in IX. We're done.
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ld a, 'N'
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jr .end
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.notanumber:
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ld a, 0xff
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jr .end
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.found:
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@ -291,11 +368,24 @@ findInGroup:
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; Compare argspec from instruction table in A with argument in (HL).
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; For constant args, it's easy: if A == (HL), it's a success.
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; If it's not this, then we check if it's a numerical arg.
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; If A is a group ID, we do something else: we check that (HL) exists in the
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; groupspec (argGrpTbl)
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matchArg:
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cp a, (hl)
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ret z
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; not an exact match, let's check for numerical constants.
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cp 'N'
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jr z, .expectsNumber
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cp 'n'
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jr z, .expectsNumber
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jr .notNumber
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.expectsNumber:
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ld a, (hl)
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cp 'N' ; In parsed arg, we don't have 'n', only 'N'
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ret ; whether we match or not, the result of Z is the good
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; one
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.notNumber:
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; A bit of a delicate situation here: we want A to go in H but also
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; (HL) to go in A. If not careful, we overwrite each other. EXX is
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; necessary to avoid invoving other registers.
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@ -336,6 +426,8 @@ matchPrimaryRow:
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; Parse line at (HL) and write resulting opcode(s) in (DE). Returns the number
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; of bytes written in A.
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;
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; Overwrites IX
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parseLine:
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call readLine
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; Check whether we have errors. We don't do any parsing if we do.
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@ -368,7 +460,6 @@ parseLine:
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; We have our matching instruction row. We're getting pretty near our
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; goal here!
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; First, let's go in IX mode. It's easier to deal with offsets here.
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push ix
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ld ixh, d
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ld ixl, e
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; First, let's see if we're dealing with a group here
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@ -409,18 +500,63 @@ parseLine:
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pop hl
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; Success!
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jr .end
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jr .writeFirstOpcode
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.notgroup:
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; not a group? easy as pie: we return the opcode directly.
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ld a, (ix+7) ; upcode is on 8th byte
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.end:
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.writeFirstOpcode:
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; At the end, we have our final opcode in A!
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pop ix
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pop de
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ld (de), a
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; Good, we are probably finished here for many primary opcodes. However,
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; some primary opcodes take 8 or 16 bit constants as an argument and
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; if that's the case here, we need to write it too.
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; We still have our instruction row in IX. Let's revisit it.
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push hl ; we use HL to point to the currently read arg
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ld a, (ix+4) ; first argspec
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ld hl, curArg1
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cp 'N'
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jr z, .withWord
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cp 'n'
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jr z, .withByte
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ld a, (ix+5) ; second argspec
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ld hl, curArg2
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cp 'N'
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jr z, .withWord
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cp 'n'
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jr z, .withByte
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; nope, no number, aright, only one opcode
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ld a, 1
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jr .end
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.withByte:
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; verify that the MSB in argument is zero
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inc hl
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inc hl ; MSB is 2nd byte
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ld a, (hl)
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dec hl ; HL now points to LSB
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cp 0
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jr nz, .numberTruncated
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; Clear to proceed. HL already points to our number
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inc de
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ldi
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ld a, 2
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jr .end
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.withWord:
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inc hl ; HL now points to LSB
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ldi ; LSB written, we point to MSB now
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ldi ; MSB written
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ld a, 3
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jr .end
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.numberTruncated:
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; problem: not zero, so value is truncated. error
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xor a
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.end:
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pop hl
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ret
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; In instruction metadata below, argument types arge indicated with a single
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; char mnemonic that is called "argspec". This is the table of correspondance.
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; Single letters are represented by themselves, so we don't need as much
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@ -523,6 +659,7 @@ instrTBlPrimary:
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.db "LD",0,0, 's', 'h', 0, 0x0a ; LD SP, HL
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.db "LD",0,0, 'l', 0xb, 0, 0b01110000 ; LD (HL), r
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.db "LD",0,0, 0xb, 'l', 3, 0b01000110 ; LD r, (HL)
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.db "LD",0,0, 'l', 'n', 0, 0x36 ; LD (HL), n
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.db "NOP", 0, 0, 0, 0, 0x00 ; NOP
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.db "OR",0,0, 'l', 0, 0, 0xb6 ; OR (HL)
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.db "OR",0,0, 0xb, 0, 0, 0b10110000 ; OR r
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@ -556,6 +693,6 @@ curArg2:
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.db 0, 0, 0
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; space for tmp stuff
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tmpVal:
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.db 0, 0, 0, 0, 0
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tmpBuf:
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.fill 0x20
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