634 lines
11 KiB
NASM
634 lines
11 KiB
NASM
; A dictionary entry has this structure:
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; - 7b name (zero-padded)
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; - 1b flags (bit 0: IMMEDIATE)
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; - 2b prev pointer
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; - 2b code pointer
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; - Parameter field (PF)
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;
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; The code pointer point to "word routines". These routines expect to be called
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; with IY pointing to the PF. They themselves are expected to end by jumping
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; to the address at the top of the Return Stack. They will usually do so with
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; "jp exit".
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; Execute a word containing native code at its PF address (PFA)
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nativeWord:
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jp (iy)
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; Execute a list of atoms, which usually ends with EXIT.
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; IY points to that list.
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compiledWord:
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push iy \ pop hl
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inc hl
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inc hl
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; HL points to next Interpreter pointer.
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call pushRS
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ld l, (iy)
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ld h, (iy+1)
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push hl \ pop iy
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; IY points to code link
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jp executeCodeLink
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; Pushes the PFA directly
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cellWord:
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push iy
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jp exit
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; Pushes the address in the first word of the PF
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sysvarWord:
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ld l, (iy)
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ld h, (iy+1)
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push hl
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jp exit
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; The word was spawned from a definition word that has a DOES>. PFA+2 (right
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; after the actual cell) is a link to the slot right after that DOES>.
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; Therefore, what we need to do push the cell addr like a regular cell, then
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; follow the link from the PFA, and then continue as a regular compiledWord.
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doesWord:
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push iy ; like a regular cell
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ld l, (iy+2)
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ld h, (iy+3)
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push hl \ pop iy
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jr compiledWord
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; The IF word checks the stack for zero. If it's non-zero, it does nothing and
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; allow compiledWord to continue.
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; If it's zero, it tracksback RS, advance it until it finds a ELSE, a THEN, or
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; an EXIT (not supposed to happen unless the IF is misconstructed). Whether
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; it's a ELSE or THEN, the same thing happens: we resume execution after the
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; ELSE/THEN. If it's a EXIT, we simply execute it.
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ifWord:
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pop hl
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ld a, h
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or l
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jp nz, exit ; non-zero, continue
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; Zero, seek ELSE, THEN or EXIT. Continue to elseWord
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; If a ELSE word is executed, it means that the preceding IF had a non-zero
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; condition and continued execution. This means that upon encountering an ELSE,
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; we must search for a THEN or an EXIT.
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; To simplify implementation and share code with ifWord, we also match ELSE,
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; which is only possible in malformed construct. Therefore "IF ELSE ELSE" is
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; valid and interpreted as "IF ELSE THEN".
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elseWord:
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; to save processing, we test EXIT, ELSE and THEN in the order they
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; appear, address-wise. This way, we don't need to push/pop HL: we can
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; SUB the difference between the words and check for zeroes.
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call popRS
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; We need to save that IP somewhere. Let it be BC
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ld b, h
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ld c, l
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.loop:
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; Whether there's a match or not, we will resume the operation at IP+2,
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; which means that we have to increase BC anyways. Let's do it now.
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inc bc \ inc bc
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call intoHL
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or a ; clear carry
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ld de, EXIT
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sbc hl, de
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jp z, exit
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; Not EXIT, let's continue with ELSE. No carry possible because EXIT
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; is first word. No need to clear.
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ld de, ELSE-EXIT
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sbc hl, de
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jr c, .nomatch ; A word between EXIT and ELSE. No match.
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jr z, .match ; We have a ELSE
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; Let's try with THEN. Again, no carry possible, C cond was handled.
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ld de, THEN-ELSE
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sbc hl, de
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jr z, .match ; We have a THEN
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.nomatch:
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; Nothing matched, which means that we need to continue looking.
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; BC is already IP+2
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ld h, b
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ld l, c
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jr .loop
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.match:
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; Matched a ELSE or a THEN, which means we need to continue executing
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; word from IP+2, which is already in BC.
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push bc \ pop iy
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jp compiledWord
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; This word does nothing. It's never going to be executed unless the wordlist
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; is misconstructed.
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thenWord:
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jp exit
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; This is not a word, but a number literal. This works a bit differently than
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; others: PF means nothing and the actual number is placed next to the
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; numberWord reference in the compiled word list. What we need to do to fetch
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; that number is to play with the Return stack: We pop it, read the number, push
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; it to the Parameter stack and then push an increase Interpreter Pointer back
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; to RS.
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numberWord:
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call popRS
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ld e, (hl)
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inc hl
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ld d, (hl)
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inc hl
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call pushRS
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push de
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jp exit
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NUMBER:
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.dw numberWord
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; Similarly to numberWord, this is not a real word, but a string literal.
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; Instead of being followed by a 2 bytes number, it's followed by a
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; null-terminated string. This is not expected to be called in a regular
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; context. Only words expecting those literals will look for them. This is why
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; the litWord triggers abort.
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litWord:
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call popRS
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call intoHL
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call printstr ; let's print the word before abort.
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ld hl, .msg
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call printstr
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jp abort
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.msg:
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.db "undefined word", 0
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LIT:
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.dw litWord
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; ( R:I -- )
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.db ";"
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.fill 7
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.dw 0
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EXIT:
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.dw nativeWord
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; When we call the EXIT word, we have to do a "double exit" because our current
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; Interpreter pointer is pointing to the word *next* to our EXIT reference when,
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; in fact, we want to continue processing the one above it.
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call popRS
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exit:
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; Before we continue: is SP within bounds?
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call chkPS
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; we're good
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call popRS
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; We have a pointer to a word
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push hl \ pop iy
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jp compiledWord
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; ( R:I -- )
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.db "QUIT"
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.fill 4
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.dw EXIT
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QUIT:
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.dw nativeWord
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quit:
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jp forthRdLine
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.db "ABORT"
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.fill 3
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.dw QUIT
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ABORT:
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.dw nativeWord
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abort:
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; Reinitialize PS (RS is reinitialized in forthInterpret
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ld sp, (INITIAL_SP)
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jp forthRdLine
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.db "BYE"
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.fill 5
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.dw ABORT
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BYE:
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.dw nativeWord
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; Goodbye Forth! Before we go, let's restore the stack
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ld sp, (INITIAL_SP)
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; unwind stack underflow buffer
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pop af \ pop af \ pop af
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; success
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xor a
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ret
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; ( c -- )
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.db "EMIT"
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.fill 4
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.dw BYE
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EMIT:
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.dw nativeWord
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pop hl
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ld a, l
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call stdioPutC
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jp exit
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; ( addr -- )
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.db "EXECUTE"
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.db 0
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.dw EMIT
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EXECUTE:
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.dw nativeWord
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pop iy ; is a wordref
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executeCodeLink:
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ld l, (iy)
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ld h, (iy+1)
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; HL points to code pointer
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inc iy
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inc iy
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; IY points to PFA
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jp (hl) ; go!
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.db ":"
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.fill 7
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.dw EXECUTE
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DEFINE:
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.dw nativeWord
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call entryhead
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ld de, compiledWord
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ld (hl), e
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inc hl
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ld (hl), d
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inc hl
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; At this point, we've processed the name literal following the ':'.
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; What's next? We have, in IP, a pointer to words that *have already
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; been compiled by INTERPRET*. All those bytes will be copied as-is.
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; All we need to do is to know how many bytes to copy. To do so, we
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; skip compwords until EXIT is reached.
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ex de, hl ; DE is our dest
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ld l, (ix)
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ld h, (ix+1)
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.loop:
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call HLPointsNUMBER
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jr nz, .notNUMBER
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; is number
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ld bc, 4
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ldir
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jr .loop
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.notNUMBER:
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call HLPointsLIT
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jr nz, .notLIT
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; is lit
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ldi
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ldi
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inc hl \ inc hl
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call strcpyM
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inc hl ; byte after word termination
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jr .loop
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.notLIT:
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; it's a word
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call HLPointsIMMED
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jr nz, .notIMMED
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; Immediate word, we'll have to call it.
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; Before we make our call, let's save our current HL/DE position
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ld (HERE), de
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ld e, (hl)
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inc hl
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ld d, (hl)
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inc hl ; point to next word
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push de \ pop iy ; prepare for executeCodeLink
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ld (ix), l
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ld (ix+1), h
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; Push return address
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ld hl, .retList
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call pushRS
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; Ready!
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jp executeCodeLink
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.notIMMED:
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; a good old regular word. We have 2 bytes to copy. But before we do,
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; let's check whether it's an EXIT. LDI doesn't affect Z, so we can
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; make our jump later.
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call HLPointsEXIT
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ldi
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ldi
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jr nz, .loop
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; HL has our new RS' TOS
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ld (ix), l
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ld (ix+1), h
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ld (HERE), de ; update HERE
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jp exit
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; This label is pushed to RS when an IMMED word is called. When that word calls
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; exit, this is where it returns. When we return, RS will need to be popped so
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; that we stay on the proper RS level.
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.retList:
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.dw .retWord
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.retWord:
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.dw .retEntry
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.retEntry:
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call popRS ; unwind stack
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; recall old HL / DE values
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ld l, (ix)
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ld h, (ix+1)
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ld de, (HERE)
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; continue!
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jr .loop
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.db "DOES>"
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.fill 3
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.dw DEFINE
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DOES:
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.dw nativeWord
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; We run this when we're in an entry creation context. Many things we
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; need to do.
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; 1. Change the code link to doesWord
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; 2. Leave 2 bytes for regular cell variable.
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; 3. Get the Interpreter pointer from the stack and write this down to
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; entry PFA+2.
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; 3. exit. Because we've already popped RS, a regular exit will abort
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; colon definition, so we're good.
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ld iy, (CURRENT)
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ld hl, doesWord
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call wrCompHL
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inc iy \ inc iy ; cell variable space
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call popRS
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call wrCompHL
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ld (HERE), iy
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jp exit
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.db "IMMEDIA"
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.db 0
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.dw DOES
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IMMEDIATE:
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.dw nativeWord
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ld hl, (CURRENT)
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dec hl
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dec hl
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dec hl
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inc (hl)
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jp exit
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; ( n -- )
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.db "LITERAL"
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.db 1 ; IMMEDIATE
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.dw IMMEDIATE
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LITERAL:
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.dw nativeWord
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ld hl, (HERE)
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ld de, NUMBER
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ld (hl), e
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inc hl
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ld (hl), d
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inc hl
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pop de ; number from stack
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ld (hl), e
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inc hl
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ld (hl), d
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inc hl
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ld (HERE), hl
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jp exit
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; ( -- c )
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.db "KEY"
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.fill 5
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.dw LITERAL
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KEY:
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.dw nativeWord
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call stdioGetC
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ld h, 0
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ld l, a
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push hl
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jp exit
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.db "INTERPR"
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.db 0
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.dw KEY
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INTERPRET:
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.dw nativeWord
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interpret:
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ld iy, COMPBUF
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.loop:
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call readword
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jr nz, .end
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call compile
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jr .loop
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.end:
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ld hl, QUIT
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call wrCompHL
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ld iy, COMPBUF
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jp compiledWord
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.db "CREATE"
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.fill 2
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.dw INTERPRET
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CREATE:
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.dw nativeWord
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call entryhead
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jp nz, quit
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ld de, cellWord
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ld (hl), e
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inc hl
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ld (hl), d
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inc hl
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ld (HERE), hl
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jp exit
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.db "HERE"
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.fill 4
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.dw CREATE
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HERE_: ; Caution: conflicts with actual variable name
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.dw sysvarWord
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.dw HERE
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.db "CURRENT"
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.db 0
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.dw HERE_
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CURRENT_:
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.dw sysvarWord
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.dw CURRENT
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; ( n -- )
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.db "."
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.fill 7
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.dw CURRENT_
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DOT:
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.dw nativeWord
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pop de
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; We check PS explicitly because it doesn't look nice to spew gibberish
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; before aborting the stack underflow.
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call chkPS
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call pad
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call fmtDecimalS
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call printstr
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jp exit
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; ( n a -- )
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.db "!"
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.fill 7
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.dw DOT
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STORE:
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.dw nativeWord
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pop iy
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pop hl
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ld (iy), l
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ld (iy+1), h
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jp exit
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; ( a -- n )
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.db "@"
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.fill 7
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.dw STORE
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FETCH:
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.dw nativeWord
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pop hl
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call intoHL
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push hl
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jp exit
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; ( a b -- b a )
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.db "SWAP"
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.fill 4
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.dw FETCH
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SWAP:
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.dw nativeWord
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pop hl
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ex (sp), hl
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push hl
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jp exit
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; ( a -- a a )
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.db "DUP"
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.fill 5
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.dw SWAP
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DUP:
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.dw nativeWord
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pop hl
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push hl
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push hl
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jp exit
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; ( a b -- a b a )
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.db "OVER"
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.fill 4
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.dw DUP
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OVER:
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.dw nativeWord
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pop hl ; B
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pop de ; A
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push de
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push hl
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push de
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jp exit
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; ( a b -- c ) A + B
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.db "+"
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.fill 7
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.dw OVER
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PLUS:
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.dw nativeWord
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pop hl
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pop de
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add hl, de
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push hl
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jp exit
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; ( a b -- c ) A - B
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.db "-"
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.fill 7
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.dw PLUS
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MINUS:
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.dw nativeWord
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pop de ; B
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pop hl ; A
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or a ; reset carry
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sbc hl, de
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push hl
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jp exit
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; ( a b -- c ) A * B
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.db "*"
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.fill 7
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.dw MINUS
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MULT:
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.dw nativeWord
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pop de
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pop bc
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call multDEBC
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push hl
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jp exit
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; ( a b -- c ) A / B
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.db "/"
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.fill 7
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.dw MULT
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DIV:
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.dw nativeWord
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pop de
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pop hl
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call divide
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push bc
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jp exit
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.db "IF"
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.fill 6
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.dw DIV
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IF:
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.dw ifWord
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.db "ELSE"
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.fill 4
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.dw IF
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ELSE:
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.dw elseWord
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.db "THEN"
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.fill 4
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.dw ELSE
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THEN:
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.dw thenWord
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; End of native words
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; ( a -- )
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; @ .
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.db "?"
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.fill 7
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.dw THEN
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FETCHDOT:
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.dw compiledWord
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.dw FETCH
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.dw DOT
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.dw EXIT
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; ( n a -- )
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; SWAP OVER @ + SWAP !
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.db "+!"
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.fill 6
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.dw FETCHDOT
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STOREINC:
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.dw compiledWord
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.dw SWAP
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.dw OVER
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.dw FETCH
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.dw PLUS
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.dw SWAP
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.dw STORE
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.dw EXIT
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; ( n -- )
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; HERE +!
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.db "ALLOT"
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.fill 3
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.dw STOREINC
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ALLOT:
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.dw compiledWord
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.dw HERE_
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.dw STOREINC
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.dw EXIT
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; CREATE 2 ALLOT
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.db "VARIABL"
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.db 0
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|
.dw ALLOT
|
|
VARIABLE:
|
|
.dw compiledWord
|
|
.dw CREATE
|
|
.dw NUMBER
|
|
.dw 2
|
|
.dw ALLOT
|
|
.dw EXIT
|
|
|
|
; ( n -- )
|
|
; CREATE HERE @ ! DOES> @
|
|
.db "CONSTAN"
|
|
.db 0
|
|
.dw VARIABLE
|
|
CONSTANT:
|
|
.dw compiledWord
|
|
.dw CREATE
|
|
.dw HERE_
|
|
.dw FETCH
|
|
.dw STORE
|
|
.dw DOES
|
|
.dw FETCH
|
|
.dw EXIT
|