Subject: [PATCH] evaluate the second argument of ALLOC_GROW only once

From: René Scharfe <[email-masked]>
Date: Fri, 15 May 2026 20:16:50 +0200

Allow the new element count passed to ALLOC_GROW to be a complex
expression with side-effects by evaluating it only once, as a parameter
to a new helper function.

Suggested-by: Junio C Hamano <[email-masked]>
Signed-off-by: René Scharfe <[email-masked]>
---
 git-compat-util.h | 20 ++++++++++++++------
 1 file changed, 14 insertions(+), 6 deletions(-)

diff --git a/git-compat-util.h b/git-compat-util.h
index ae1bdc90a4..2bc1f43f48 100644
--- a/git-compat-util.h
+++ b/git-compat-util.h
@@ -812,6 +812,16 @@ static inline void move_array(void *dst, const void *src, size_t n, size_t size)
 
 #define alloc_nr(x) (((x)+16)*3/2)
 
+static inline bool st_alloc_nr(size_t nr, size_t alloc, size_t *outp)
+{
+	if (nr > alloc) {
+		size_t out = alloc_nr(alloc);
+		*outp = out < nr ? nr : out;
+		return true;
+	}
+	return false;
+}
+
 /**
  * Dynamically growing an array using realloc() is error prone and boring.
  *
@@ -857,12 +867,10 @@ static inline void move_array(void *dst, const void *src, size_t n, size_t size)
  */
 #define ALLOC_GROW(x, nr, alloc) \
 	do { \
-		if ((nr) > alloc) { \
-			if (alloc_nr(alloc) < (nr)) \
-				alloc = (nr); \
-			else \
-				alloc = alloc_nr(alloc); \
-			REALLOC_ARRAY(x, alloc); \
+		size_t alloc_grow_new_alloc_; \
+		if (st_alloc_nr((nr), (alloc), &alloc_grow_new_alloc_)) { \
+			alloc = alloc_grow_new_alloc_; \
+			REALLOC_ARRAY(x, alloc_grow_new_alloc_); \
 		} \
 	} while (0)
 
-- 
2.54.0