2 files changed, 109 insertions(+), 1 deletions(-)

M .gitignore
A onward.s

@@ 1,2 1,2 @@
 *.o
-forth
+onward

@@ 0,0 1,108 @@
+; vi: ft=nasm
+
+; https://blog.rchapman.org/posts/Linux_System_Call_Table_for_x86_64/
+
+;
+
+global _start
+section .text
+%define SYS_READ 0
+%define SYS_WRITE 1
+%define SYS_EXIT 60
+
+%define STDIN 0
+%define STDOUT 1
+
+_start:
+
+rep_loop:
+        ;; write prompt
+        mov rax, SYS_WRITE
+        mov rdi, STDOUT
+        mov rsi, prompt
+        mov rdx, prompt_len
+        syscall
+
+        ;; read input string
+        mov rax, SYS_READ
+        mov rdi, STDIN
+        mov rsi, in_buf
+        mov rdx, buf_len
+        syscall
+
+        mov rdx, rax                ; length in rax
+
+        cmp rdx, 0                  ; exit if empty (user sent Ctrl-D)
+        jz exit
+
+        ;; get the first word in the string
+        ;; while calculating hash of string
+
+        ; update hash (sdbm hash):
+        ;   for c in str:
+        ;     new_hash = c + (hash << 6) + (hash << 16) - hash
+        ;     hash = new_hash
+
+        mov rbx, word_buf           ; word_ptr:   rbx = (char *) word_buf
+        mov rcx, 0                  ; hash:       rcx = 0
+                                    ; in_buf_ptr: rsi (set above)
+
+read_next_word_loop:
+        mov rax, 0                  ; clear rax
+        mov al, [rsi]               ; c = *in_buf_ptr
+        cmp al, byte ' '            ; check for whitespace
+        je .end
+        cmp al, byte `\n`
+        je .end
+        cmp al, byte `\t`
+        je .end
+        mov [rbx], al               ; *word_buf = c
+
+        ; rdx = new_hash (copy of hash for iteration)
+        ; rax = current character (because of al)
+
+        ; calculate hash
+        mov rdx, rcx                ; rdx = hash. copied so we can shift it around
+        sal rdx, 6                  ; hash << 6
+        add rax, rdx
+        sal rdx, 10                 ; hash << 16
+        add rax, rdx
+        sub rax, rcx                ; - hash
+        mov rcx, rax                ; hash = new_hash
+
+        add rsi, 1                  ; in_buf_ptr++
+        add rbx, 1                  ; word_ptr++
+        jmp read_next_word_loop
+.end:
+        ; calculate len, store it in rdx
+        mov rdx, rbx
+        sub rdx, word_buf
+
+        ; TODO: store value into intern table
+        ; TODO: push symbol value onto stack
+        ; TODO: bootstrap
+        ; TODO: jit self
+
+        ;; echo word
+        mov rax, SYS_WRITE
+        mov rdi, STDOUT
+        mov rsi, word_buf
+        ; rdx set above
+        syscall
+
+        jmp rep_loop
+
+exit:
+        mov rax, SYS_EXIT
+        mov rdi, 0
+        syscall
+
+section .bss
+        in_buf: resb 128
+        buf_len: equ $ - in_buf
+
+        word_buf: resb 32
+
+section .rodata
+        prompt: db "> "
+        prompt_len: equ $ - prompt