diff --git a/src/debug.cpp b/src/debug.cpp
new file mode 100644
index 0000000..42e5edb
--- /dev/null
+++ b/src/debug.cpp
@@ -0,0 +1,462 @@
+//===-------------------------- debug.cpp ---------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#define _LIBCPP_DEBUG2
+#include "__debug"
+#include "functional"
+#include "algorithm"
+#include "__hash_table"
+#include "mutex"
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+_LIBCPP_VISIBLE
+__libcpp_db*
+__get_db()
+{
+    static __libcpp_db db;
+    return &db;
+};
+
+_LIBCPP_VISIBLE
+const __libcpp_db*
+__get_const_db()
+{
+    return __get_db();
+}
+
+namespace
+{
+
+typedef mutex mutex_type;
+// struct mutex_type
+// {
+//     void lock() {}
+//     void unlock() {};
+// };
+typedef lock_guard<mutex_type> WLock;
+typedef lock_guard<mutex_type> RLock;
+
+mutex_type&
+mut()
+{
+    static mutex_type m;
+    return m;
+}
+
+}  // unnamed namespace
+
+__i_node::~__i_node()
+{
+    if (__next_)
+    {
+        __next_->~__i_node();
+        free(__next_);
+    }
+}
+
+__c_node::~__c_node()
+{
+    free(beg_);
+    if (__next_)
+    {
+        __next_->~__c_node();
+        free(__next_);
+    }
+}
+
+__libcpp_db::__libcpp_db()
+    : __cbeg_(nullptr),
+      __cend_(nullptr),
+      __csz_(0),
+      __ibeg_(nullptr),
+      __iend_(nullptr),
+      __isz_(0)
+{
+}
+
+__libcpp_db::~__libcpp_db()
+{
+    if (__cbeg_)
+    {
+        for (__c_node** p = __cbeg_; p != __cend_; ++p)
+        {
+            if (*p != nullptr)
+            {
+                (*p)->~__c_node();
+                free(*p);
+            }
+        }
+        free(__cbeg_);
+    }
+    if (__ibeg_)
+    {
+        for (__i_node** p = __ibeg_; p != __iend_; ++p)
+        {
+            if (*p != nullptr)
+            {
+                (*p)->~__i_node();
+                free(*p);
+            }
+        }
+        free(__ibeg_);
+    }
+}
+
+void*
+__libcpp_db::__find_c_from_i(void* __i) const
+{
+    RLock _(mut());
+    __i_node* i = __find_iterator(__i);
+    return i != nullptr ? (i->__c_ != nullptr ? i->__c_->__c_ : nullptr) : nullptr;
+}
+
+void
+__libcpp_db::__insert_ic(void* __i, const void* __c)
+{
+    WLock _(mut());
+    __i_node* i = __insert_iterator(__i);
+    _LIBCPP_ASSERT(__cbeg_ != __cend_, "debug mode internal logic error __insert_ic A");
+    size_t hc = hash<const void*>()(__c) % (__cend_ - __cbeg_);
+    __c_node* c = __cbeg_[hc];
+    _LIBCPP_ASSERT(c != nullptr, "debug mode internal logic error __insert_ic B");
+    while (c->__c_ != __c)
+    {
+        c = c->__next_;
+        _LIBCPP_ASSERT(c != nullptr, "debug mode internal logic error __insert_ic C");
+    }
+    c->__add(i);
+    i->__c_ = c;
+}
+
+__c_node*
+__libcpp_db::__insert_c(void* __c)
+{
+    WLock _(mut());
+    if (__csz_ + 1 > __cend_ - __cbeg_)
+    {
+        size_t nc = __next_prime(2*(__cend_ - __cbeg_) + 1);
+        __c_node** cbeg = (__c_node**)calloc(nc, sizeof(void*));
+        if (cbeg == nullptr)
+            throw bad_alloc();
+        for (__c_node** p = __cbeg_; p != __cend_; ++p)
+        {
+            __c_node* q = *p;
+            while (q != nullptr)
+            {
+                size_t h = hash<void*>()(q->__c_) % nc;
+                __c_node* r = q->__next_;
+                q->__next_ = cbeg[h];
+                cbeg[h] = q;
+                q = r;
+            }
+        }
+        free(__cbeg_);
+        __cbeg_ = cbeg;
+        __cend_ = __cbeg_ + nc;
+    }
+    size_t hc = hash<void*>()(__c) % (__cend_ - __cbeg_);
+    __c_node* p = __cbeg_[hc];
+    __c_node* r = __cbeg_[hc] = (__c_node*)malloc(sizeof(__c_node));
+    if (__cbeg_[hc] == nullptr)
+        throw bad_alloc();
+    r->__c_ = __c;
+    r->__next_ = p;
+    ++__csz_;
+    return r;
+}
+
+void
+__libcpp_db::__erase_i(void* __i)
+{
+    WLock _(mut());
+    if (__ibeg_ != __iend_)
+    {
+        size_t hi = hash<void*>()(__i) % (__iend_ - __ibeg_);
+        __i_node* p = __ibeg_[hi];
+        if (p != nullptr)
+        {
+            __i_node* q = nullptr;
+            while (p->__i_ != __i)
+            {
+                q = p;
+                p = p->__next_;
+                if (p == nullptr)
+                    return;
+            }
+            if (q == nullptr)
+                __ibeg_[hi] = p->__next_;
+            else
+                q->__next_ = p->__next_;
+            __c_node* c = p->__c_;
+            free(p);
+            --__isz_;
+            if (c != nullptr)
+                c->__remove(p);
+        }
+    }
+}
+
+void
+__libcpp_db::__invalidate_all(void* __c)
+{
+    WLock _(mut());
+    size_t hc = hash<void*>()(__c) % (__cend_ - __cbeg_);
+    __c_node* p = __cbeg_[hc];
+    _LIBCPP_ASSERT(p != nullptr, "debug mode internal logic error __invalidate_all A");
+    while (p->__c_ != __c)
+    {
+        p = p->__next_;
+        _LIBCPP_ASSERT(p != nullptr, "debug mode internal logic error __invalidate_all B");
+    }
+    while (p->end_ != p->beg_)
+    {
+        --p->end_;
+        (*p->end_)->__c_ = nullptr;
+    }
+}
+
+__c_node*
+__libcpp_db::__find_c_and_lock(void* __c) const
+{
+    mut().lock();
+    size_t hc = hash<void*>()(__c) % (__cend_ - __cbeg_);
+    __c_node* p = __cbeg_[hc];
+    _LIBCPP_ASSERT(p != nullptr, "debug mode internal logic error __find_c_and_lock A");
+    while (p->__c_ != __c)
+    {
+        p = p->__next_;
+        _LIBCPP_ASSERT(p != nullptr, "debug mode internal logic error __find_c_and_lock B");
+    }
+    return p;
+}
+
+void
+__libcpp_db::unlock() const
+{
+    mut().unlock();
+}
+
+void
+__libcpp_db::__erase_c(void* __c)
+{
+    WLock _(mut());
+    size_t hc = hash<void*>()(__c) % (__cend_ - __cbeg_);
+    __c_node* p = __cbeg_[hc];
+    __c_node* q = nullptr;
+    _LIBCPP_ASSERT(p != nullptr, "debug mode internal logic error __erase_c A");
+    while (p->__c_ != __c)
+    {
+        q = p;
+        p = p->__next_;
+        _LIBCPP_ASSERT(p != nullptr, "debug mode internal logic error __erase_c B");
+    }
+    if (q == nullptr)
+        __cbeg_[hc] = p->__next_;
+    else
+        q->__next_ = p->__next_;
+    while (p->end_ != p->beg_)
+    {
+        --p->end_;
+        (*p->end_)->__c_ = nullptr;
+    }
+    free(p->beg_);
+    free(p);
+    --__csz_;
+}
+
+void
+__libcpp_db::__iterator_copy(void* __i, const void* __i0)
+{
+    WLock _(mut());
+    __i_node* i = __find_iterator(__i);
+    __i_node* i0 = __find_iterator(__i0);
+    __c_node* c0 = i0 != nullptr ? i0->__c_ : nullptr;
+    if (i == nullptr && c0 != nullptr)
+        i = __insert_iterator(__i);
+    __c_node* c = i != nullptr ? i->__c_ : nullptr;
+    if (c != c0)
+    {
+        if (c != nullptr)
+            c->__remove(i);
+        if (i != nullptr)
+        {
+            i->__c_ = nullptr;
+            if (c0 != nullptr)
+            {
+                i->__c_ = c0;
+                i->__c_->__add(i);
+            }
+        }
+    }
+}
+
+bool
+__libcpp_db::__dereferenceable(const void* __i) const
+{
+    RLock _(mut());
+    __i_node* i = __find_iterator(__i);
+    return i != nullptr && i->__c_ != nullptr && i->__c_->__dereferenceable(__i);
+}
+
+bool
+__libcpp_db::__decrementable(const void* __i) const
+{
+    RLock _(mut());
+    __i_node* i = __find_iterator(__i);
+    return i != nullptr && i->__c_ != nullptr && i->__c_->__decrementable(__i);
+}
+
+bool
+__libcpp_db::__addable(const void* __i, ptrdiff_t __n) const
+{
+    RLock _(mut());
+    __i_node* i = __find_iterator(__i);
+    return i != nullptr && i->__c_ != nullptr && i->__c_->__addable(__i, __n);
+}
+
+bool
+__libcpp_db::__subscriptable(const void* __i, ptrdiff_t __n) const
+{
+    RLock _(mut());
+    __i_node* i = __find_iterator(__i);
+    return i != nullptr && i->__c_ != nullptr && i->__c_->__subscriptable(__i, __n);
+}
+
+bool
+__libcpp_db::__comparable(const void* __i, const void* __j) const
+{
+    RLock _(mut());
+    __i_node* i = __find_iterator(__i);
+    __i_node* j = __find_iterator(__j);
+    __c_node* ci = i != nullptr ? i->__c_ : nullptr;
+    __c_node* cj = j != nullptr ? j->__c_ : nullptr;
+    return ci != nullptr && ci == cj;
+}
+
+void
+__libcpp_db::swap(void* c1, void* c2)
+{
+    WLock _(mut());
+    size_t hc = hash<void*>()(c1) % (__cend_ - __cbeg_);
+    __c_node* p1 = __cbeg_[hc];
+    _LIBCPP_ASSERT(p1 != nullptr, "debug mode internal logic error swap A");
+    while (p1->__c_ != c1)
+    {
+        p1 = p1->__next_;
+        _LIBCPP_ASSERT(p1 != nullptr, "debug mode internal logic error swap B");
+    }
+    hc = hash<void*>()(c2) % (__cend_ - __cbeg_);
+    __c_node* p2 = __cbeg_[hc];
+    _LIBCPP_ASSERT(p2 != nullptr, "debug mode internal logic error swap C");
+    while (p2->__c_ != c2)
+    {
+        p2 = p2->__next_;
+        _LIBCPP_ASSERT(p2 != nullptr, "debug mode internal logic error swap D");
+    }
+    std::swap(p1->beg_, p2->beg_);
+    std::swap(p1->end_, p2->end_);
+    std::swap(p1->cap_, p2->cap_);
+    for (__i_node** p = p1->beg_; p != p1->end_; ++p)
+        (*p)->__c_ = p1;
+    for (__i_node** p = p2->beg_; p != p2->end_; ++p)
+        (*p)->__c_ = p2;
+}
+
+// private api
+
+_LIBCPP_HIDDEN
+__i_node*
+__libcpp_db::__insert_iterator(void* __i)
+{
+    if (__isz_ + 1 > __iend_ - __ibeg_)
+    {
+        size_t nc = __next_prime(2*(__iend_ - __ibeg_) + 1);
+        __i_node** ibeg = (__i_node**)calloc(nc, sizeof(void*));
+        if (ibeg == nullptr)
+            throw bad_alloc();
+        for (__i_node** p = __ibeg_; p != __iend_; ++p)
+        {
+            __i_node* q = *p;
+            while (q != nullptr)
+            {
+                size_t h = hash<void*>()(q->__i_) % nc;
+                __i_node* r = q->__next_;
+                q->__next_ = ibeg[h];
+                ibeg[h] = q;
+                q = r;
+            }
+        }
+        free(__ibeg_);
+        __ibeg_ = ibeg;
+        __iend_ = __ibeg_ + nc;
+    }
+    size_t hi = hash<void*>()(__i) % (__iend_ - __ibeg_);
+    __i_node* p = __ibeg_[hi];
+    __i_node* r = __ibeg_[hi] = (__i_node*)malloc(sizeof(__i_node));
+    if (r == nullptr)
+        throw bad_alloc();
+    ::new(r) __i_node(__i, p, nullptr);
+    ++__isz_;
+    return r;
+}
+
+_LIBCPP_HIDDEN
+__i_node*
+__libcpp_db::__find_iterator(const void* __i) const
+{
+    __i_node* r = nullptr;
+    if (__ibeg_ != __iend_)
+    {
+        size_t h = hash<const void*>()(__i) % (__iend_ - __ibeg_);
+        for (__i_node* nd = __ibeg_[h]; nd != nullptr; nd = nd->__next_)
+        {
+            if (nd->__i_ == __i)
+            {
+                r = nd;
+                break;
+            }
+        }
+    }
+    return r;
+}
+
+_LIBCPP_HIDDEN
+void
+__c_node::__add(__i_node* i)
+{
+    if (end_ == cap_)
+    {
+        size_t nc = 2*(cap_ - beg_);
+        if (nc == 0)
+            nc = 1;
+        __i_node** beg = (__i_node**)malloc(nc * sizeof(__i_node*));
+        if (beg == nullptr)
+            throw bad_alloc();
+        if (nc > 1)
+            memcpy(beg, beg_, nc/2*sizeof(__i_node*));
+        free(beg_);
+        beg_ = beg;
+        end_ = beg_ + nc/2;
+        cap_ = beg_ + nc;
+    }
+    *end_++ = i;
+}
+
+_LIBCPP_HIDDEN
+void
+__c_node::__remove(__i_node* p)
+{
+    __i_node** r = find(beg_, end_, p);
+    _LIBCPP_ASSERT(r != end_, "debug mode internal logic error __c_node::__remove");
+    if (--end_ != r)
+        memmove(r, r+1, (end_ - r)*sizeof(__i_node*));
+}
+
+_LIBCPP_END_NAMESPACE_STD