equeue: align passed-in buffer

Make equeue_create_inplace align the passed-in buffer and size to
sizeof(void *).

Really we should be aiming to align more for ARM, as blocks should be
8-byte aligned, but the internal heap mechanisms only work to 4-byte
alignment at the moment. More work would be needed to ensure 8-byte
alignment of allocated blocks.

equeue.c

@@ -7,9 +7,9 @@
 #include "equeue.h"
 
 #include <stdlib.h>
+#include <stdint.h>
 #include <string.h>
 
-
 // calculate the relative-difference between absolute times while
 // correctly handling overflow conditions
 static inline int equeue_tickdiff(unsigned a, unsigned b) {
@@ -47,7 +47,11 @@ int equeue_create(equeue_t *q, size_t size) {
 
 int equeue_create_inplace(equeue_t *q, size_t size, void *buffer) {
     // setup queue around provided buffer
-    q->buffer = buffer;
+    // ensure buffer and size are aligned
+    q->buffer = (void *)(((uintptr_t) buffer + sizeof(void *) -1) & ~(sizeof(void *) -1));
+    size -= (char *) q->buffer - (char *) buffer;
+    size &= ~(sizeof(void *) -1);
+
     q->allocated = 0;
 
     q->npw2 = 0;
@@ -57,7 +61,7 @@ int equeue_create_inplace(equeue_t *q, size_t size, void *buffer) {
 
     q->chunks = 0;
     q->slab.size = size;
-    q->slab.data = buffer;
+    q->slab.data = q->buffer;
 
     q->queue = 0;
     q->tick = equeue_tick();