feat: implement substraction between pointers

2 files changed, 16 insertions, 2 deletions

diff --git a/main.c b/main.c
index 48f391c..ef19587 100644
--- a/main.c
+++ b/main.c
@@ -1459,8 +1459,15 @@ AstNode* parse_additive_expr(Parser* p) {
             next_token(p);
             rhs = parse_multiplicative_expr(p);
             if (lhs->ty->kind == TypeKind_ptr) {
-                lhs = ast_new_binary_expr(
-                    op, lhs, ast_new_binary_expr(TokenKind_star, rhs, ast_new_int(type_sizeof(lhs->ty->to))));
+                if (rhs->ty->kind == TypeKind_ptr) {
+                    // (a - b) / sizeof(a)
+                    lhs = ast_new_binary_expr(TokenKind_slash, ast_new_binary_expr(op, lhs, rhs),
+                                              ast_new_int(type_sizeof(lhs->ty->to)));
+                } else {
+                    // a - b*sizeof(a)
+                    lhs = ast_new_binary_expr(
+                        op, lhs, ast_new_binary_expr(TokenKind_star, rhs, ast_new_int(type_sizeof(lhs->ty->to))));
+                }
             } else {
                 lhs = ast_new_binary_expr(op, lhs, rhs);
             }
diff --git a/tests/024.sh b/tests/024.sh
index 99557e1..20453a0 100644
--- a/tests/024.sh
+++ b/tests/024.sh
@@ -1,6 +1,9 @@
 set -e
 
 cat <<'EOF' > expected
+3
+3
+3
 EOF
 bash ../../test_diff.sh <<'EOF'
 int printf();
@@ -29,6 +32,10 @@ int main() {
     lp1 = &l;
     lp2 = &l + 3;
 
+    printf("%d\n", cp2 - cp1);
+    printf("%d\n", ip2 - ip1);
+    printf("%d\n", lp2 - lp1);
+
     return 0;
 }
 EOF