X-Git-Url: https://git.rrq.au/?a=blobdiff_plain;ds=sidebyside;f=main.asm;h=f466a104d0b7caaba7e2f9f5f7ddfcf284a53e23;hb=38ab2f16dd683ac65c0567f3d7a079dcdc3edf2f;hp=0a8ff4cf256dcd602e3c8c59b3bde3418422343b;hpb=8d5c5f5affc85bae309c04f096b65a87c2f33cb6;p=rrq%2Fjonasforth.git diff --git a/main.asm b/main.asm index 0a8ff4c..f466a10 100644 --- a/main.asm +++ b/main.asm @@ -50,6 +50,38 @@ EXIT: popr rsi next +;; LIT is a special word that reads the next "word pointer" and causes it to be +;; placed on the stack rather than executed. +LIT: + dq .start +.start: + lodsq + 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. +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 .start: @@ -65,44 +97,265 @@ EMIT: popr rsi next -PUSH_HELLO_CHARS: +;; Prints a newline to standard output. +NEWLINE: + dq docol + dq LIT, $A + 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: dq .start - .start: - push $A - push 'o' - push 'l' - push 'l' - push 'e' - push 'H' +.start: + 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 + + mov rsi, [.rsi] + mov rax, [.rax] + next -HELLO: +;; 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 PUSH_HELLO_CHARS - dq EMIT - dq EMIT - dq EMIT - dq EMIT - dq EMIT - dq EMIT + 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 .start +.start: + mov rbx, rsi + mov rcx, rax + + mov rax, 1 + mov rdi, 1 + pop rdx ; Length + pop rsi ; Buffer + syscall + + mov rax, rcx + mov rsi, rbx + next + +;; Exit the program cleanly. TERMINATE: dq .start - .start: +.start: mov rax, $3C mov rdi, 0 syscall +PUSH_HELLO_CHARS: + dq docol + dq LIT, $A + dq LIT, 'o' + dq LIT, 'l' + dq LIT, 'l' + dq LIT, 'e' + dq LIT, 'H' + dq EXIT + +PUSH_YOU_TYPED: + dq .start +.start: + push you_typed_string + push you_typed_string.length + next + +HELLO: + dq docol + dq LIT, 'H', EMIT + dq LIT, 'e', EMIT + dq LIT, 'l', EMIT + dq LIT, 'l', EMIT + dq LIT, 'o', EMIT + dq LIT, '!', EMIT + 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 HELLO - dq HELLO + dq READ_NUMBER, DOTU, NEWLINE + dq BRANCH, -8 * 4 dq TERMINATE segment readable writable +you_typed_string db 'You typed: ' +.length = $ - you_typed_string + +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 ? + +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: