sign-compare: avoid comparing ptrdiff with an int/unsigned

Instead, offset the base pointer with integer and compare it with
the other pointer.

Signed-off-by: Junio C Hamano <[email protected]>

Author: gitster

shallow.c

@@ -534,7 +534,7 @@ static uint32_t *paint_alloc(struct paint_info *info)
 	unsigned nr = DIV_ROUND_UP(info->nr_bits, 32);
 	unsigned size = nr * sizeof(uint32_t);
 	void *p;
-	if (!info->pool_count || size > info->end - info->free) {
+	if (!info->pool_count || info->end < info->free + size) {
 		if (size > POOL_SIZE)
 			BUG("pool size too small for %d in paint_alloc()",
 			    size);