push rax
next
-;; 0BRANCH is the fundamental mechanism for branching. If the top of the stack
-;; is zero, we jump by the given offset. 0BRANCH is given the offset as an
-;; integer after the word.
+;; BRANCH is the fundamental mechanism for branching. BRANCH reads the next word
+;; as a signed integer literal and jumps by that offset.
+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:
cmp rax, 0
jnz .dont_branch
.do_branch:
- 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
+ jmp BRANCH.start
.dont_branch:
add rsi, 8 ; We need to skip over the next word, which contains the offset.
next
;; 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.
TELL:
dq NEWLINE
dq EXIT
+;; .U prints the value on the stack as an unsigned integer in hexadecimal.
+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 TELL
- dq TELL
- dq NEWLINE
- dq HELLO
+ dq READ_NUMBER, DOTU, NEWLINE
+ dq BRANCH, -8 * 4
dq TERMINATE
segment readable writable
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