From 4777ee0c8591986380f8e6c161f15536c3d0af21 Mon Sep 17 00:00:00 2001
From: Daniel Micay <danielmicay@gmail.com>
Date: Sat, 25 Aug 2018 15:21:50 -0400
Subject: [PATCH] special case division for page size slabs

---
 malloc.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/malloc.c b/malloc.c
index a3225bf..d516f25 100644
--- a/malloc.c
+++ b/malloc.c
@@ -292,7 +292,12 @@ static void *get_slab(struct size_class *c, size_t slab_size, struct slab_metada
 
 static struct slab_metadata *get_metadata(struct size_class *c, size_t slab_size, void *p) {
     size_t offset = (char *)p - (char *)c->class_region_start;
-    size_t index = offset / slab_size;
+    size_t index;
+    if (slab_size == PAGE_SIZE) {
+        index = offset >> PAGE_SHIFT;
+    } else {
+        index = offset / slab_size;
+    }
     // still caught without this check either as a read access violation or "double free"
     if (index >= c->metadata_allocated) {
         fatal_error("invalid free within a slab yet to be used");