From 1bb2b6ccfc11d4aec61287441379cb6584b8fb5f Mon Sep 17 00:00:00 2001
From: Tavian Barnes <tavianator@tavianator.com>
Date: Thu, 31 Aug 2023 10:42:42 -0400
Subject: alloc: New varena_grow() function

---
 src/alloc.c | 15 +++++++++++++++
 src/alloc.h | 14 ++++++++++++++
 2 files changed, 29 insertions(+)

diff --git a/src/alloc.c b/src/alloc.c
index 8a4dc3a..0b978ba 100644
--- a/src/alloc.c
+++ b/src/alloc.c
@@ -283,6 +283,21 @@ void *varena_realloc(struct varena *varena, void *ptr, size_t old_count, size_t
 	return ret;
 }
 
+void *varena_grow(struct varena *varena, void *ptr, size_t *count) {
+	size_t old_count = *count;
+
+	// Round up to the limit of the current size class.  If we're already at
+	// the limit, go to the next size class.
+	size_t new_shift = varena_size_class(varena, old_count + 1) + varena->shift;
+	size_t new_count = (size_t)1 << new_shift;
+
+	ptr = varena_realloc(varena, ptr, old_count, new_count);
+	if (ptr) {
+		*count = new_count;
+	}
+	return ptr;
+}
+
 void varena_free(struct varena *varena, void *ptr, size_t count) {
 	struct arena *arena = varena_get(varena, count);
 	arena_free(arena, ptr);
diff --git a/src/alloc.h b/src/alloc.h
index b5dfa68..5f0c423 100644
--- a/src/alloc.h
+++ b/src/alloc.h
@@ -270,6 +270,20 @@ void *varena_alloc(struct varena *varena, size_t count);
  */
 void *varena_realloc(struct varena *varena, void *ptr, size_t old_count, size_t new_count);
 
+/**
+ * Grow a flexible struct by an arbitrary amount.
+ *
+ * @param varena
+ *         The varena to allocate from.
+ * @param ptr
+ *         The object to resize.
+ * @param count
+ *         Pointer to the flexible array length.
+ * @return
+ *         The resized struct, or NULL on failure.
+ */
+void *varena_grow(struct varena *varena, void *ptr, size_t *count);
+
 /**
  * Free an arena-allocated flexible struct.
  *
-- 
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