;; 'dq' statements.)
macro forth label, name {
header label, name
- dq docol
+ dq DOCOL
}
segment readable executable
+entry main
+
+include "impl.asm"
+
main:
cld ; Clear direction flag so LODSQ does the right thing.
mov rbp, return_stack_top ; Initialize return stack
- mov rsi, program
- next
+ mov rax, MAIN
+ jmp qword [rax]
program: dq MAIN
;; The codeword is the code that will be executed at the beginning of a forth
;; word. It needs to save the old RSI and update it to point to the next word to
;; execute.
-docol:
+header DOCOL, 'DOCOL'
pushr rsi ; Save old value of RSI on return stack; we will continue execution there after we are done executing this word
lea rsi, [rax + 8] ; RAX currently points to the address of the codeword, so we want to continue at RAX+8
next ; Execute word pointed to by RSI
;; This word is called at the end of a Forth definition. It just needs to
-;; restore the old value of RSI (saved by 'docol') and resume execution.
+;; restore the old value of RSI (saved by 'DOCOL') and resume execution.
forth_asm EXIT, 'EXIT'
popr rsi
next
;; dictionary entry for that word. If no such word exists, return 0.
forth_asm FIND, 'FIND'
mov [.rsi], rsi
- pop [.search_length]
- pop [.search_buffer]
- ;; RSI contains the entry we are currently looking at
+ pop [find.search_length]
+ pop [find.search_buffer]
mov rsi, [latest_entry] ; Start with the last added word
+ call find
+ push rsi
-.loop:
- movzx rcx, byte [rsi + 8] ; Length of word being looked at
- cmp rcx, [.search_length]
- jne .next ; If the words don't have the same length, we have the wrong word
-
- ;; Otherwise, we need to compare strings
- lea rdx, [rsi + 8 + 1] ; Location of character being compared in entry
- mov rdi, [.search_buffer] ; Location of character being compared in search buffer
-.compare_char:
- mov al, [rdx]
- mov ah, [rdi]
- cmp al, ah
- jne .next ; They don't match; try again
- inc rdx ; These characters match; look at the next ones
- inc rdi
- loop .compare_char
-
- jmp .found ; They match! We are done.
-
-.next:
- mov rsi, [rsi] ; Look at the previous entry
- cmp rsi, 0
- jnz .loop ; If there is no previous word, exit and return 0
-
-.found:
+ mov rsi, [.rsi]
+ next
push rsi
mov rsi, [.rsi]
next
+;; Given an entry in the dictionary, return a pointer to the codeword of that
+;; entry.
+forth_asm TCFA, '>CFA'
+ pop rax
+ add rax, 8 ; [rax] = length of name
+ movzx rbx, byte [rax]
+ inc rax
+ add rax, rbx ; [rax] = codeword
+ push rax
+ next
+
;; BRANCH is the fundamental mechanism for branching. BRANCH reads the next word
;; as a signed integer literal and jumps by that offset.
forth_asm BRANCH, 'BRANCH'
add rsi, 8 ; We need to skip over the next word, which contains the offset.
next
+;; Duplicate the top of the stack.
+forth_asm DUP_, 'DUP'
+ push qword [rsp]
+ next
+
+;; Execute the codeword at the given address.
+forth_asm EXEC, 'EXEC'
+ pop rax
+ jmp qword [rax]
+
;; Expects a character on the stack and prints it to standard output.
forth_asm EMIT, 'EMIT'
pushr rsi
;; size. The pointer is valid until the next call to READ_WORD.
forth_asm READ_WORD, 'READ-WORD'
mov [.rsi], rsi
- mov [.rax], rax
-.skip_whitespace:
- ;; Read characters into .char_buffer until one of them is not whitespace.
- mov rax, 0
- mov rdi, 0
- mov rsi, .char_buffer
- mov rdx, 1
- syscall
-
- cmp [.char_buffer], ' '
- je .skip_whitespace
- cmp [.char_buffer], $A
- je .skip_whitespace
-
-.alpha:
- ;; We got a character that wasn't whitespace. Now read the actual word.
- mov [.length], 0
-
-.read_alpha:
- mov al, [.char_buffer]
- movzx rbx, [.length]
- mov rsi, .buffer
- add rsi, rbx
- mov [rsi], al
- inc [.length]
-
- mov rax, 0
- mov rdi, 0
- mov rsi, .char_buffer
- mov rdx, 1
- syscall
-
- cmp [.char_buffer], ' '
- je .end
- cmp [.char_buffer], $A
- jne .read_alpha
-
-.end:
- push .buffer
- movzx rax, [.length]
- push rax
+ call read_word
+ push rdi ; Buffer
+ push rdx ; Length
mov rsi, [.rsi]
- mov rax, [.rax]
-
next
;; Takes a string on the stack and replaces it with the decimal number that the
;; string represents.
forth_asm PARSE_NUMBER, 'PARSE-NUMBER'
- pop [.length] ; Length
- pop rdi ; String pointer
- mov r8, 0 ; Result
-
- ;; Add (10^(rcx-1) * parse_char(rdi[length - rcx])) to the accumulated value
- ;; for each rcx.
- mov rcx, [.length]
-.loop:
- ;; First, calcuate 10^(rcx - 1)
- mov rax, 1
-
- mov r9, rcx
- .exp_loop:
- dec r9
- jz .break
- mov rbx, 10
- mul rbx
- jmp .exp_loop
- .break:
-
- ;; Now, rax = 10^(rcx - 1).
-
- ;; We need to calulate the value of the character at rdi[length - rcx].
- mov rbx, rdi
- add rbx, [.length]
- sub rbx, rcx
- movzx rbx, byte [rbx]
- sub rbx, '0'
-
- ;; Multiply this value by rax to get (10^(rcx-1) * parse_char(rdi[length - rcx])),
- ;; then add this to the result.
- mul rbx
-
- ;; Add that value to r8
- add r8, rax
+ pop [parse_number.length] ; Length
+ pop [parse_number.buffer] ; String pointer
- dec rcx
- jnz .loop
-
- push r8
+ push rsi
+ call parse_number
+ pop rsi
+ push rax ; Result
next
forth READ_NUMBER, 'READ-NUMBER'
dq NEWLINE
dq EXIT
+;; Duplicate a pair of elements.
+forth_asm PAIRDUP, '2DUP'
+ pop rbx
+ pop rax
+ push rax
+ push rbx
+ push rax
+ push rbx
+ next
+
+;; Swap the top two elements on the stack.
+forth_asm SWAP, 'SWAP'
+ pop rax
+ pop rbx
+ push rax
+ push rbx
+ next
+
+;; Remove the top element from the stack.
+forth_asm DROP, 'DROP'
+ add rsp, 8
+ next
+
+;; The INTERPRET word reads and interprets user input. It's behavior depends on
+;; the current STATE. It provides special handling for integers. (TODO)
+forth INTERPRET, 'INTERPRET'
+ ;; Read word
+ dq READ_WORD
+ dq PAIRDUP
+ ;; Stack is (word length word length).
+ dq FIND ; Try to find word
+ dq DUP_
+ dq ZBRANCH, 8 * 8 ; Check if word is found
+
+ ;; Word is found, execute it
+ dq TCFA
+ ;; Stack is (word length addr)
+ dq SWAP, DROP
+ dq SWAP, DROP
+ ;; Stack is (addr)
+ dq EXEC
+ dq EXIT
+
+ ;; No word is found, assume it is an integer literal
+ ;; Stack is (word length addr)
+ dq DROP
+ dq PARSE_NUMBER
+ dq EXIT
+
;; .U prints the value on the stack as an unsigned integer in hexadecimal.
forth_asm DOTU, '.U'
mov [.length], 0
pop rsi
next
+;; Takes a value and an address, and stores the value at the given address.
+forth_asm PUT, '!'
+ pop rbx ; Address
+ pop rax ; Value
+ mov [rbx], rax
+ next
+
+;; Takes an address and returns the value at the given address.
+forth_asm GET, '@'
+ pop rax
+ mov rax, [rax]
+ push rax
+ next
+
+;; Add two integers on the stack.
+forth_asm PLUS, '+'
+ pop rax
+ pop rbx
+ add rax, rbx
+ push rax
+ next
+
+;; Calculate difference between two integers on the stack. The second number is
+;; subtracted from the first.
+forth_asm MINUS, '-'
+ pop rax
+ pop rbx
+ sub rbx, rax
+ push rbx
+ next
+
+;; Get the location of the STATE variable. It can be set with '!' and read with
+;; '@'.
+forth STATE, 'STATE'
+ dq LIT, var_STATE
+ dq EXIT
+
+;; Get the location of the LATEST variable. It can be set with '!' and read with
+;; '@'.
+forth LATEST, 'LATEST'
+ dq LIT, latest_entry
+ dq EXIT
+
+;; Get the location at which compiled words are expected to be added. This
+;; pointer is usually modified automatically when calling ',', but we can also
+;; read it manually with 'HERE'.
+forth HERE, 'HERE'
+ dq LIT, here
+ dq EXIT
+
+forth COMMA, ','
+ dq HERE, GET, PUT ; Set the memory at the address pointed to by HERE
+ dq HERE, GET, LIT, 8, PLUS ; Calculate new address for HERE to point to
+ dq HERE, PUT ; Update HERE to point to the new address
+ dq EXIT
+
+;; Read user input until next " character is found. Push a string containing the
+;; input on the stack as (buffer length). Note that the buffer is only valid
+;; until the next call to S" and that no more than 255 character can be read.
+forth_asm READ_STRING, 'S"'
+ push rsi
+
+ mov [.length], 0
+
+.read_char:
+ mov rax, 0
+ mov rdi, 0
+ mov rsi, .char_buffer
+ mov rdx, 1
+ syscall
+
+ mov al, [.char_buffer]
+ cmp al, '"'
+ je .done
+
+ mov rdx, .buffer
+ add rdx, [.length]
+ mov [rdx], al
+ inc [.length]
+ jmp .read_char
+
+.done:
+ pop rsi
+
+ push .buffer
+ push [.length]
+
+ next
+
+;; CREATE inserts a new header in the dictionary, and updates LATEST so that it
+;; points to the header. To compile a word, the user can then call ',' to
+;; continue to append data after the header.
+;;
+;; It takes the name of the word as a string (address length) on the stack.
+forth_asm CREATE, 'CREATE'
+ pop rcx ; Word string length
+ pop rdx ; Word string pointer
+
+ mov rdi, [here] ; rdi = Address at which to insert this entry
+ mov rax, [latest_entry] ; rax = Address of the previous entry
+ mov [rdi], rax ; Insert link to previous entry
+ mov [latest_entry], rdi ; Update LATEST to point to this word
+
+ add rdi, 8
+ mov [rdi], rcx ; Insert length
+
+ ;; Insert word string
+ add rdi, 1
+
+ push rsi
+ mov rsi, rdx ; rsi = Word string pointer
+ rep movsb
+ pop rsi
+
+ ;; Update HERE
+ mov [here], rdi
+
+ next
+
forth MAIN, 'MAIN'
dq HELLO
- dq READ_WORD, FIND, DOTU, NEWLINE
- dq BRANCH, -8 * 5
+ dq INTERPRET
+ dq BRANCH, -8 * 2
dq TERMINATE
segment readable writable
+;; The LATEST variable holds a pointer to the word that was last added to the
+;; dictionary. This pointer is updated as new words are added, and its value is
+;; used by FIND to look up words.
latest_entry dq initial_latest_entry
-SPACE_string db 'SPACE'
-.length = $ - SPACE_string
-HELLO_string db 'HELLO'
-.length = $ - HELLO_string
-DOTU_string db '.U'
-.length = $ - DOTU_string
-HELLA_string db 'HELLA'
-.length = $ - HELLA_string
+;; The STATE variable is 0 when the interpreter is executing, and non-zero when
+;; it is compiling.
+var_STATE dq 0
-
-you_typed_string db 'You typed: '
-.length = $ - you_typed_string
-
-FIND.search_length dq ?
-FIND.search_buffer dq ?
FIND.rsi dq ?
READ_WORD.rsi dq ?
-READ_WORD.rax dq ?
-READ_WORD.max_size = $FF
-READ_WORD.buffer rb READ_WORD.max_size
-READ_WORD.length db ?
-READ_WORD.char_buffer db ?
+READ_WORD.rbp dq ?
+
+READ_STRING.char_buffer db ?
+READ_STRING.buffer rb $FF
+READ_STRING.length dq ?
DOTU.chars db '0123456789ABCDEF'
DOTU.buffer rq 16 ; 64-bit number has no more than 16 digits in hex
DOTU.length dq ?
DOTU.printed_length dq ?
-PARSE_NUMBER.length dq ?
+;; Reserve space for compiled words, accessed through HERE.
+here dq here_top
+here_top rq $2000
;; Return stack
rq $2000