;; 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.
+EXIT_entry:
+ dq 0
+ db 4
+ db 'EXIT'
EXIT:
dq .start
.start:
;; LIT is a special word that reads the next "word pointer" and causes it to be
;; placed on the stack rather than executed.
+LIT_entry:
+ dq EXIT_entry
+ db 3
+ db 'LIT'
LIT:
dq .start
.start:
push rax
next
+;; Given a string (a pointer following by a size), return the location of the
+;; dictionary entry for that word. If no such word exists, return 0.
+FIND_entry:
+ dq LIT_entry
+ db 4
+ db 'FIND'
+FIND:
+ dq .start
+.start:
+ mov [.rsi], rsi
+ pop [.search_length]
+ pop [.search_buffer]
+
+ ;; RSI contains the entry we are currently looking at
+ mov rsi, [latest_entry] ; Start with the last added word
+
+.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:
+ push rsi
+
+ mov rsi, [.rsi]
+ next
+
+;; BRANCH is the fundamental mechanism for branching. BRANCH reads the next word
+;; as a signed integer literal and jumps by that offset.
+BRANCH_entry:
+ dq FIND_entry
+ db 6
+ db 'BRANCH'
+BRANCH:
+ dq .start
+.start:
+ add rsi, [rsi] ; [RSI], which is the next word, contains the offset; we add this to the instruction pointer.
+ next ; Then, we can just continue execution as normal
+
+;; 0BRANCH is like BRANCH, but it jumps only if the top of the stack is zero.
+ZBRANCH:
+ dq .start
+.start:
+ ;; Compare top of stack to see if we should branch
+ pop rax
+ cmp rax, 0
+ jnz .dont_branch
+.do_branch:
+ jmp BRANCH.start
+.dont_branch:
+ add rsi, 8 ; We need to skip over the next word, which contains the offset.
+ next
+
;; Expects a character on the stack and prints it to standard output.
EMIT:
dq .start
dq EMIT
dq EXIT
+;; Prints a space to standard output.
+SPACE_entry:
+ dq BRANCH_entry
+ db 5
+ db 'SPACE'
+SPACE:
+ dq docol
+ dq LIT, ' '
+ dq EMIT
+ dq EXIT
+
;; Read a word from standard input and push it onto the stack as a pointer and a
;; size. The pointer is valid until the next call to READ_WORD.
-READ_WORD: ; 400170
+READ_WORD:
dq .start
.start:
mov [.rsi], rsi
next
+;; Takes a string on the stack and replaces it with the decimal number that the
+;; string represents.
+PARSE_NUMBER:
+ dq .start
+.start:
+ 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
+
+ dec rcx
+ jnz .loop
+
+ push r8
+
+ next
+
+READ_NUMBER:
+ dq docol
+ dq READ_WORD
+ dq PARSE_NUMBER
+ dq EXIT
+
;; Takes a string (in the form of a pointer and a length on the stack) and
;; prints it to standard output.
-TYPE:
+TELL:
dq .start
.start:
mov rbx, rsi
push you_typed_string.length
next
+HELLO_entry:
+ dq SPACE_entry
+ db 5
+ db 'HELLO'
HELLO:
dq docol
dq LIT, 'H', EMIT
dq NEWLINE
dq EXIT
+;; .U prints the value on the stack as an unsigned integer in hexadecimal.
+DOTU_entry:
+ dq HELLO_entry
+ db 2
+ db '.U'
+DOTU:
+ dq .start
+.start:
+ mov [.length], 0
+ mov [.printed_length], 1
+ pop rax ; RAX = value to print
+ push rsi ; Save value of RSI
+
+ ;; We start by constructing the buffer to print in reverse
+
+.loop:
+ mov rdx, 0
+ mov rbx, $10
+ div rbx ; Put remainer in RDX and quotient in RAX
+
+ ;; Place the appropriate character in the buffer
+ mov rsi, .chars
+ add rsi, rdx
+ mov bl, [rsi]
+ mov rdi, .rbuffer
+ add rdi, [.length]
+ mov [rdi], bl
+ inc [.length]
+
+ ;; .printed_length is the number of characters that we ulitmately want to
+ ;; print. If we have printed a non-zero character, then we should update
+ ;; .printed_length.
+ cmp bl, '0'
+ je .skip_updating_real_length
+ mov rbx, [.length]
+ mov [.printed_length], rbx
+.skip_updating_real_length:
+
+ cmp [.length], 16
+ jle .loop
+
+ ;; Flip buffer around, since it is currently reversed
+ mov rcx, [.printed_length]
+.flip:
+ mov rsi, .rbuffer
+ add rsi, rcx
+ dec rsi
+ mov al, [rsi]
+
+ mov rdi, .buffer
+ add rdi, [.printed_length]
+ sub rdi, rcx
+ mov [rdi], al
+
+ loop .flip
+
+ ;; Print the buffer
+ mov rax, 1
+ mov rdi, 1
+ mov rsi, .buffer
+ mov rdx, [.printed_length]
+ syscall
+
+ ;; Restore RSI and continue execution
+ pop rsi
+ next
+
MAIN:
dq docol
dq HELLO
- dq READ_WORD
- dq LIT, you_typed_string
- dq LIT, you_typed_string.length
- dq TYPE
- dq TYPE
- dq NEWLINE
- dq HELLO
+ dq LIT, SPACE_entry, DOTU, NEWLINE
+ dq LIT, HELLO_entry, DOTU, NEWLINE
+ dq LIT, DOTU_entry, DOTU, NEWLINE
+ dq LIT, SPACE_string, LIT, SPACE_string.length, TELL, SPACE
+ dq LIT, SPACE_string, LIT, SPACE_string.length, FIND, DOTU, NEWLINE
+ dq LIT, HELLO_string, LIT, HELLO_string.length, TELL, SPACE
+ dq LIT, HELLO_string, LIT, HELLO_string.length, FIND, DOTU, NEWLINE
+ dq LIT, DOTU_string, LIT, DOTU_string.length, TELL, SPACE
+ dq LIT, DOTU_string, LIT, DOTU_string.length, FIND, DOTU, NEWLINE
+ dq LIT, HELLA_string, LIT, HELLA_string.length, TELL, SPACE
+ dq LIT, HELLA_string, LIT, HELLA_string.length, FIND, DOTU, NEWLINE
dq TERMINATE
segment readable writable
+latest_entry dq DOTU_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
+
+
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.length db ?
READ_WORD.char_buffer db ?
+DOTU.chars db '0123456789ABCDEF'
+DOTU.buffer rq 16 ; 64-bit number has no more than 16 digits in hex
+DOTU.rbuffer rq 16
+DOTU.length dq ?
+DOTU.printed_length dq ?
+
+PARSE_NUMBER.length dq ?
+
;; Return stack
rq $2000
return_stack_top:
projects / rrq / jonasforth.git / blobdiff