From 5b1b3bec3f25ea5fc1f48c269f300c4211a1bac7 Mon Sep 17 00:00:00 2001
From: Jon Santmyer <jon@jonsantmyer.com>
Date: Fri, 19 Apr 2024 16:11:24 -0400
Subject: initial commit; mostly documented.

---
 realloc.c | 66 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 66 insertions(+)
 create mode 100644 realloc.c

(limited to 'realloc.c')

diff --git a/realloc.c b/realloc.c
new file mode 100644
index 0000000..1b78e9e
--- /dev/null
+++ b/realloc.c
@@ -0,0 +1,66 @@
+#include "malloc.h"
+#include <assert.h>
+#include <string.h>
+
+void*
+__realloc_impl(heap_cache_t *cache, void *ptr, size_t w)
+{
+    if(w == 0) {
+        DBGPRINT("realloc: called with w == 0, freeing %p\n", ptr);
+        __free_impl(cache, ptr);
+        return NULL;
+    }
+    if(ptr == NULL) {
+        DBGPRINT("realloc: called with NULL ptr, alloc %i\n", w);
+        return __malloc_impl(cache, w);
+    }
+
+    w = REALW(w);
+    bucket_obj_t *obj = OBJ_FROM_PTR(ptr);
+
+    assert(OBJ_VALID(obj));
+    size_t objw = OBJ_WIDTH(obj);
+    if(objw > w) return ptr;
+
+    size_t wdiff = w - objw;
+    DBGPRINT("realloc: ptr %p needs %i new bytes\n", ptr, wdiff);
+
+    bucket_obj_t *after = OBJ_AFTER(obj);
+    size_t afterw = 0;
+    bucket_t *bucket = __bucket_from_obj(cache, obj);
+    void *newptr = NULL;
+
+    if(bucket == NULL)
+        goto resize_fail;
+
+    if((uintptr_t)after > bucket->limit) goto resize_fail;
+    assert(OBJ_VALID(after));
+    afterw = OBJ_WIDTH(after);
+
+    if(OBJ_TAKEN(after))
+        goto resize_fail;
+    
+    DBGPRINT("realloc: obj %p after obj %p is free (w %i)\n", after, obj, afterw);
+    if(objw + sizeof(bucket_obj_t) + afterw < w)
+        goto resize_fail;
+
+    obj->size_taken = w | 1;
+    if(bucket->firstfree == after)
+        bucket->firstfree = OBJ_AFTER(obj);
+
+    after = OBJ_AFTER(obj);
+    *after = (bucket_obj_t){
+        .checksum = OBJ_CHECKSUM,
+        .size_taken = afterw - wdiff
+    };
+    DBGPRINT("realloc: moved obj %p (%i) to resize obj %p (%i)\n", 
+            after, after->size_taken, obj, obj->size_taken);
+    return ptr;
+
+resize_fail:
+    DBGPRINT("realloc: could not resize existing object, calling malloc\n");
+    newptr = __malloc_impl(cache, w);
+    memcpy(newptr, ptr, obj->size_taken & ~1);
+    __free_impl(cache, ptr);
+    return newptr;
+}
-- 
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