mem-pool: simplify alignment calculation

Commit Message

René Scharfe Dec. 24, 2023, 5:02 p.m. UTC

Use DIV_ROUND_UP in mem_pool_alloc() to round the allocation length to
the next multiple of GIT_MAX_ALIGNMENT instead of twiddling bits
explicitly.  This is shorter and clearer, to the point that we no longer
need the comment that explains what's being calculated.

Signed-off-by: René Scharfe <[e-mail]>
---
Latest Clang emits the same x64 instructions for both versions; GCC only
emits the supposedly optimal output for the patched version:
https://godbolt.org/z/jPscnPqna

 mem-pool.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

--
2.43.0

Patch

diff --git a/mem-pool.c b/mem-pool.c
index 2b25521e2d..2078c22b09 100644
--- a/mem-pool.c
+++ b/mem-pool.c
@@ -89,9 +89,7 @@  void *mem_pool_alloc(struct mem_pool *pool, size_t len)
 	struct mp_block *p = NULL;
 	void *r;

-	/* round up to a 'GIT_MAX_ALIGNMENT' alignment */
-	if (len & (GIT_MAX_ALIGNMENT - 1))
-		len += GIT_MAX_ALIGNMENT - (len & (GIT_MAX_ALIGNMENT - 1));
+	len = DIV_ROUND_UP(len, GIT_MAX_ALIGNMENT) * GIT_MAX_ALIGNMENT;

 	if (pool->mp_block &&
 	    pool->mp_block->end - pool->mp_block->next_free >= len)