From de60e52c5af08d57cf83b5b110ec19562aa41b17 Mon Sep 17 00:00:00 2001
From: andromeda <andromeda@lenovo>
Date: Wed, 18 Mar 2026 16:21:34 +0100
Subject: [PATCH] range check char length

---
 twasm/asm/main.asm  | 5 +++--
 twasm/asm/tests.asm | 9 +++++++++
 2 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/twasm/asm/main.asm b/twasm/asm/main.asm
index f4f13af..ead107e 100644
--- a/twasm/asm/main.asm
+++ b/twasm/asm/main.asm
@@ -866,7 +866,8 @@ evaluate_constant:
     jmp .bin_loop
 
   .chr:
-    ; TODO range check rcx
+    cmp rcx, 4       ; ensure char is only 4 bytes long
+    jg .unrecognised
     cmp rsi, 1 ; range check
     je .chr_break
 
@@ -896,7 +897,7 @@ evaluate_constant:
     jmp .chr_break
 
   .chr_break_for_good:
-    mov dl, [rdi]
+    mov dl, [rdi] ; make sure the chr is closed
     cmp dl, '"'
     jne .unrecognised
 
diff --git a/twasm/asm/tests.asm b/twasm/asm/tests.asm
index df60eb4..c4cd545 100644
--- a/twasm/asm/tests.asm
+++ b/twasm/asm/tests.asm
@@ -377,6 +377,13 @@ test_evaluate_constant:
   cmp rdx, 0x03
   jne .fail
 
+  ; oversized char
+  mov rdi, .case1c
+  mov rsi, 7
+  call evaluate_constant
+  cmp rdx, 0xFF
+  jne .fail
+
   .pass:
     mov rsi, msg_pass
     call print
@@ -396,6 +403,8 @@ test_evaluate_constant:
   .case3h_solution dq 0x243F6A8885A308D3
   .case0c db '"char"'
   .case0c_solution dq "char"
+  .case1c db '"chars"'
+  .case1c_solution dq "chars"
 
   .case0q db "0q31103755242102"
   .case0q_solution dq 0q31103755242102