[PATCH 2/4] shallow.c: avoid theoretical pointer wrap-around

The expression info->free+size is technically undefined behaviour in
exactly the case we want to test for. Moreover, the compiler is likely
to translate the expression to

  (unsigned long)info->free + size > (unsigned long)info->end

where there's at least a theoretical chance that the LHS could wrap
around 0, giving a false negative.

This might as well be written using pointer subtraction avoiding these
issues.

Signed-off-by: Rasmus Villemoes <redacted>
---
 shallow.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/shallow.c b/shallow.c
index e21534a..8b1c35d 100644
--- a/shallow.c
+++ b/shallow.c

@@ -444,7 +444,7 @@ static uint32_t *paint_alloc(struct paint_info *info)
 	unsigned nr = (info->nr_bits + 31) / 32;
 	unsigned size = nr * sizeof(uint32_t);
 	void *p;
-	if (!info->slab_count || info->free + size > info->end) {
+	if (!info->slab_count || size > info->end - info->free) {
 		unsigned alloc_size = size < COMMIT_SLAB_SIZE ?
 			COMMIT_SLAB_SIZE : size;
 		info->slab_count++;

-- 
2.1.4