From 269014e7843fabf395fca10c3364e50825f0fe20 Mon Sep 17 00:00:00 2001
From: spl3g <spleefer6@yandex.ru>
Date: Wed, 19 Mar 2025 18:08:58 +0300
Subject: Add arena string builder

---
 lib/arena.h         | 38 ++++++++++++++++++++++++++------------
 lib/arena_strings.h | 19 +++++++++++++++++++
 2 files changed, 45 insertions(+), 12 deletions(-)

diff --git a/lib/arena.h b/lib/arena.h
index 7535f8a..1f53355 100644
--- a/lib/arena.h
+++ b/lib/arena.h
@@ -34,18 +34,32 @@ void *arena_realloc(arena *a, void *oldptr, size_t oldsz, size_t newsz);
 #define ARENA_REGION_DEFAULT_CAPACITY (8*1024)
 #define ARENA_DA_INIT_CAP (2)
 
-#define arena_da_append(a, da, item)												\
-    do {																			\
-        if ((da)->len >= (da)->cap) {												\
-            size_t new_cap = (da)->cap == 0 ? ARENA_DA_INIT_CAP : (da)->cap*2;		\
-            (da)->data = arena_realloc(												\
-                (a), (da)->data,													\
-                (da)->cap*sizeof(*(da)->data),										\
-                new_cap*sizeof(*(da)->data));										\
-            (da)->cap = new_cap;													\
-        }																			\
-																					\
-        (da)->data[(da)->len++] = (item);											\
+#define arena_da_reserve(a, da, expected_size)								\
+    do {																	\
+        if ((expected_size) >= (da)->cap) {									\
+        size_t new_cap = (da)->cap == 0 ? ARENA_DA_INIT_CAP : (da)->cap*2;	\
+        while (new_cap < expected_size) {									\
+            new_cap *= 2;													\
+        }																	\
+        (da)->data = arena_realloc(											\
+             (a), (da)->data,												\
+             (da)->cap*sizeof(*(da)->data),									\
+             new_cap*sizeof(*(da)->data));									\
+        (da)->cap = new_cap;												\
+        }																	\
+    } while (0)
+
+#define arena_da_append(a, da, item)				\
+    do {											\
+        arena_da_reserve((a), (da), (da)->len + 1);	\
+        (da)->data[(da)->len++] = (item);			\
+    } while (0)
+
+#define arena_da_append_many(a, da, items, items_len)							\
+    do {																		\
+        arena_da_reserve((a), (da), (da)->len+len);								\
+        memcpy((da)->data+(da)->len, (items), sizeof(*(da)->data)*items_len);	\
+        (da)->len += len;														\
     } while (0)
 
 #endif //ARENA_H_
diff --git a/lib/arena_strings.h b/lib/arena_strings.h
index 85ffda3..b25435d 100644
--- a/lib/arena_strings.h
+++ b/lib/arena_strings.h
@@ -10,8 +10,27 @@ typedef struct {
   size_t cap;
 } const_string_da;
 
+typedef struct {
+  char* data;
+  size_t len;
+  size_t cap;
+} string_builder;
+
 const_string arena_cs_append(arena *a, const_string dst, const_string src);
 const_string arena_cs_init(arena *a, int len);
 const_string arena_cs_concat(arena *a, const_string_da strings, const_string sep);
 
+#define arena_sb_append_buf(a, sb, buf, len) arena_da_append_many((a), (sb), (buf), (len))
+
+#define arena_sb_append_cstr(a, sb, cstr)				\
+    do {												\
+        const char * str = (cstr);						\
+        size_t len = strlen((cstr));					\
+        arena_da_append_many((a), (sb), (str), len);	\
+    } while (0)
+
+#define arena_sb_append_null(a, sb)	arena_da_append_many((a), (sb), "", 1)
+
+#define arena_sb_to_cs(sb) cs_from_parts((sb).data, (sb).len)
+
 #endif // ARENA_STRINGS_H_
-- 
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