diff -r b7d1317b138e -r fae240d633fc src/stack.c
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/stack.c	Tue Oct 17 16:15:41 2017 +0200
@@ -0,0 +1,144 @@
+/*
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER.
+ *
+ * Copyright 2017 Olaf Wintermann. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ *   1. Redistributions of source code must retain the above copyright
+ *      notice, this list of conditions and the following disclaimer.
+ *
+ *   2. Redistributions in binary form must reproduce the above copyright
+ *      notice, this list of conditions and the following disclaimer in the
+ *      documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "ucx/stack.h"
+
+#include <string.h>
+
+static size_t ucx_stack_align(size_t n) {
+    int align = n % sizeof(void*);
+    if (align) {
+        n += sizeof(void*) - align;
+    }
+    return n;
+}
+
+void ucx_stack_init(UcxStack *stack, char* space, size_t size) {
+    stack->size = size - size % sizeof(void*);
+    stack->space = space;
+    stack->top = NULL;
+    
+    stack->allocator.pool = stack;
+    stack->allocator.malloc = (ucx_allocator_malloc) ucx_stack_malloc;
+    stack->allocator.calloc = (ucx_allocator_calloc) ucx_stack_calloc;
+    stack->allocator.realloc = (ucx_allocator_realloc) ucx_stack_realloc;
+    stack->allocator.free = (ucx_allocator_free) ucx_stack_free;
+}
+
+void *ucx_stack_malloc(UcxStack *stack, size_t n) {
+
+    if (ucx_stack_avail(stack) < ucx_stack_align(n)) {
+        return NULL;
+    } else {
+        char *prev = stack->top;
+        if (stack->top) {
+            stack->top += ucx_stack_align(ucx_stack_topsize(stack));
+        } else {
+            stack->top = stack->space;
+        }
+        
+        ((struct ucx_stack_metadata*)stack->top)->prev = prev;
+        ((struct ucx_stack_metadata*)stack->top)->size = n;
+        stack->top += sizeof(struct ucx_stack_metadata);
+        
+        return stack->top;
+    }
+}
+
+void *ucx_stack_calloc(UcxStack *stack, size_t nelem, size_t elsize) {
+    void *mem = ucx_stack_malloc(stack, nelem*elsize);
+    memset(mem, 0, nelem*elsize);
+    return mem;
+}
+
+void *ucx_stack_realloc(UcxStack *stack, void *ptr, size_t n) {
+    if (ptr == stack->top) {
+        if (stack->size - (stack->top - stack->space) < ucx_stack_align(n)) {
+            return NULL;
+        } else {
+            ((struct ucx_stack_metadata*)stack->top - 1)->size = n;
+            return ptr;
+        }
+    } else {
+        if (ucx_stack_align(((struct ucx_stack_metadata*)ptr - 1)->size) <
+                ucx_stack_align(n)) {
+            void *nptr = ucx_stack_malloc(stack, n);
+            if (nptr) {
+                memcpy(nptr, ptr, n);
+                ucx_stack_free(stack, ptr);
+                
+                return nptr;
+            } else {
+                return NULL;
+            }
+        } else {
+            ((struct ucx_stack_metadata*)ptr - 1)->size = n;
+            return ptr;
+        }
+    }
+}
+
+void ucx_stack_free(UcxStack *stack, void *ptr) {
+    if (ptr == stack->top) {
+        stack->top = ((struct ucx_stack_metadata*) stack->top - 1)->prev;
+    } else {
+        struct ucx_stack_metadata *next = (struct ucx_stack_metadata*)(
+            (char*)ptr +
+            ucx_stack_align(((struct ucx_stack_metadata*) ptr - 1)->size)
+        );
+        next->prev = ((struct ucx_stack_metadata*) ptr - 1)->prev;
+    }
+}
+
+void ucx_stack_popn(UcxStack *stack, void *dest, size_t n) {
+    if (ucx_stack_empty(stack)) {
+        return;
+    }
+    
+    size_t len = ucx_stack_topsize(stack);
+    if (len > n) {
+        len = n;
+    }
+    
+    memcpy(dest, stack->top, len);
+    
+    ucx_stack_free(stack, stack->top);
+}
+
+size_t ucx_stack_avail(UcxStack *stack) {
+    size_t avail = ((stack->top ? (stack->size
+                    - (stack->top - stack->space)
+                    - ucx_stack_align(ucx_stack_topsize(stack)))
+                    : stack->size));
+    
+    if (avail > sizeof(struct ucx_stack_metadata)) {
+        return avail - sizeof(struct ucx_stack_metadata);
+    } else {
+        return 0;
+    }
+}