From d51de0cc1da2beebfb2773078f5f7c47f773d9d5 Mon Sep 17 00:00:00 2001
From: andromeda <andromeda@lenovo>
Date: Thu, 26 Mar 2026 21:11:23 +0100
Subject: [PATCH] buffer writes, add to example

---
 twasm/asm/main.asm | 77 ++++++++++++++++++++++++++++++++++++++++------
 1 file changed, 67 insertions(+), 10 deletions(-)

diff --git a/twasm/asm/main.asm b/twasm/asm/main.asm
index 69708bc..9c052e1 100644
--- a/twasm/asm/main.asm
+++ b/twasm/asm/main.asm
@@ -90,6 +90,7 @@ assemble:
   mov [.tokens_total], edi     ; edi = total number of tokens in table
 
   .loop:
+    call .flush_write_buffer
     call .get_next_tte
     ; di = tte
     call get_tte_type
@@ -129,7 +130,7 @@ assemble:
     call get_opcode
     ; al = opcode
     ; dl = 0x00
-    call .output_byte
+    call .write_byte
 
     jmp .loop_next_token
 
@@ -143,7 +144,7 @@ assemble:
     ; al = opcode
     ; dl = op flag
     push rdx
-    call .output_byte
+    call .write_byte
     pop rdx ; dl = op flag
 
     call .next_token
@@ -165,7 +166,7 @@ assemble:
     cmp al, 0x02 ; type: register
     je .operator_1_register
 
-    jmp .loop_next_token
+    jmp .unexpected_token
 
   .operator_1_memory:
     mov rsi, .msg_operator_1_memory
@@ -183,7 +184,7 @@ assemble:
     mov edx, 11b    ; dl = mod bits
     call get_ModRM
     ; al = Mod R/M byte
-    call .output_byte
+    call .write_byte
 
     jmp .loop_next_token
 
@@ -212,7 +213,7 @@ assemble:
     cmp al, 0x02 ; type: register
     je .operator_2_register
 
-    jmp .loop_next_token
+    jmp .unexpected_token
 
   .operator_2_memory:
     mov rsi, .msg_operator_2_memory
@@ -226,7 +227,7 @@ assemble:
     call get_opcode
     ; al = opcode
     ; dl = op flag
-    call .output_byte
+    call .write_byte
 
     call .next_token
     jge .break
@@ -264,7 +265,7 @@ assemble:
     mov dl, 00b ; dl = mod bits
     call get_ModRM
     ; al = Mod R/M byte
-    call .output_byte
+    call .write_byte
 
     jmp .loop_next_token
 
@@ -279,7 +280,7 @@ assemble:
     ; al = opcode
     ; dl = op flag
     ; TODO do something if the op flag is present
-    call .output_byte
+    call .write_byte
     pop rdi ; di = dst tte
 
     mov si, di ; si = dst tte
@@ -324,7 +325,7 @@ assemble:
     mov edx, 00b ; dl = mod bits
     call get_ModRM
     ; al = Mod R/M byte
-    call .output_byte
+    call .write_byte
 
     jmp .loop_next_token
 
@@ -338,7 +339,7 @@ assemble:
     mov edx, 11b ; dl = mod bits
     call get_ModRM
     ; al = Mod R/M byte
-    call .output_byte
+    call .write_byte
 
     jmp .loop_next_token
 
@@ -348,6 +349,7 @@ assemble:
     jmp .loop
 
   .break:
+    call .flush_write_buffer
     ret
 
   .unexpected_token:
@@ -391,6 +393,59 @@ assemble:
   .next_output_byte dd OUTPUT_ADDR ; next empty byte in output
                                    ; TODO get rid of this sketchy bit of state
 
+  ; al = byte to push
+  .push_byte:
+    push rcx
+    mov ecx, [.buffer_pointer]
+    push rcx
+    push rax
+    mov ecx, .buffer_end
+    mov [.buffer_pointer], ecx
+    .push_byte_loop:
+      dec ecx
+      cmp ecx, .buffer
+      jl .push_byte_break
+      mov al, [ecx]
+      mov [ecx + 1], al
+      jmp .push_byte_loop
+    .push_byte_break:
+      pop rax ; al = byte to push
+      mov [.buffer], al
+      pop rcx ; ecx = old buffer pointer
+      inc ecx
+      mov [.buffer_pointer], ecx
+      pop rcx
+      ret
+
+  ; al = byte to write
+  .write_byte:
+    mov edx, [.buffer_pointer]
+    mov [edx], al
+    inc edx
+    mov [.buffer_pointer], edx
+    ret
+
+  .flush_write_buffer:
+    push rcx
+    push rax
+    mov ecx, [.buffer_pointer]
+    .flush_write_buffer_loop:
+      dec ecx
+      cmp ecx, .buffer
+      jl .flush_write_buffer_break
+      mov al, [ecx]
+      call .output_byte
+      mov byte [ecx], 0x00
+      jmp .flush_write_buffer_loop
+    .flush_write_buffer_break
+      mov dword [.buffer_pointer], .buffer
+      pop rax
+      pop rcx
+      ret
+  .buffer dq 0, 0            ; octo word of space for max of 8 bytes per write
+  .buffer_end:
+  .buffer_pointer dd .buffer ; points to current byte in buffer
+
   .msg_unexpected_token db "unexpected token, aborting", 0x0A, 0x00
   .msg_unsupported_memory_access db "unsupported memory access, aborting", 0x0A, 0x00
   .msg_operator_0 db "operator_0", 0x0A, 0x00
@@ -1991,6 +2046,8 @@ program:
   db "; one line comment", 0x0A
   db "mov rdx, [rax]", 0x0A
   db "mov [rax], rdx", 0x0A
+  db "mov [rcx], rbx", 0x0A
+  db "mov rcx, [rbx]", 0x0A
   db "hlt", 0x0A
   .size dq $ - program