Adding upstream version 3.2.1.upstream/3.2.1upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 912 insertions, 0 deletions

diff --git a/lib/generic/trie.c b/lib/generic/trie.c
new file mode 100644
index 0000000..0009eef
--- /dev/null
+++ b/lib/generic/trie.c
@@ -0,0 +1,912 @@
+/*  Copyright (C) 2016-2018 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+    The code originated from https://github.com/fanf2/qp/blob/master/qp.c
+    at revision 5f6d93753.
+ */
+
+#include <assert.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "lib/generic/trie.h"
+#include "lib/utils.h"
+#include "contrib/ucw/lib.h"
+
+#if defined(__i386) || defined(__x86_64) || defined(_M_IX86) \
+	|| (defined(__BYTE_ORDER__) && defined(__ORDER_LITTLE_ENDIAN) \
+		&& __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__)
+
+	/*!
+	 * \brief Use a pointer alignment hack to save memory.
+	 *
+	 * When on, isbranch() relies on the fact that in leaf_t the first pointer
+	 * is aligned on multiple of 4 bytes and that the flags bitfield is
+	 * overlaid over the lowest two bits of that pointer.
+	 * Neither is really guaranteed by the C standards; the second part should
+	 * be OK with x86_64 ABI and most likely any other little-endian platform.
+	 * It would be possible to manipulate the right bits portably, but it would
+	 * complicate the code nontrivially. C++ doesn't even guarantee type-punning.
+	 * In debug mode we check this works OK when creating a new trie instance.
+	 */
+	#define FLAGS_HACK 1
+#else
+	#define FLAGS_HACK 0
+#endif
+
+typedef unsigned char byte;
+#ifndef uint
+typedef unsigned int uint;
+#define uint uint
+#endif
+typedef uint bitmap_t; /*! Bit-maps, using the range of 1<<0 to 1<<16 (inclusive). */
+
+typedef struct {
+	uint32_t len; // 32 bits are enough for key lengths; probably even 16 bits would be.
+	char chars[];
+} tkey_t;
+
+/*! \brief Leaf of trie. */
+typedef struct {
+	#if !FLAGS_HACK
+		byte flags;
+	#endif
+	tkey_t *key; /*!< The pointer must be aligned to 4-byte multiples! */
+	trie_val_t val;
+} leaf_t;
+
+/*! \brief A trie node is either leaf_t or branch_t. */
+typedef union node node_t;
+
+/*!
+ * \brief Branch node of trie.
+ *
+ * - The flags distinguish whether the node is a leaf_t (0), or a branch
+ *   testing the more-important nibble (1) or the less-important one (2).
+ * - It stores the index of the byte that the node tests.  The combined
+ *   value (index*4 + flags) increases in branch nodes as you go deeper
+ *   into the trie.  All the keys below a branch are identical up to the
+ *   nibble identified by the branch.  Indices have to be stored because
+ *   we skip any branch nodes that would have a single child.
+ *   (Consequently, the skipped parts of key have to be validated in a leaf.)
+ * - The bitmap indicates which subtries are present.  The present child nodes
+ *   are stored in the twigs array (with no holes between them).
+ * - To simplify storing keys that are prefixes of each other, the end-of-string
+ *   position is treated as another nibble value, ordered before all others.
+ *   That affects the bitmap and twigs fields.
+ *
+ * \note The branch nodes are never allocated individually, but they are
+ *   always part of either the root node or the twigs array of the parent.
+ */
+typedef struct {
+	#if FLAGS_HACK
+		uint32_t flags  : 2,
+		         bitmap : 17; /*!< The first bitmap bit is for end-of-string child. */
+	#else
+		byte flags;
+		uint32_t bitmap;
+	#endif
+	uint32_t index;
+	node_t *twigs;
+} branch_t;
+
+union node {
+	leaf_t leaf;
+	branch_t branch;
+};
+
+struct trie {
+	node_t root; // undefined when weight == 0, see empty_root()
+	size_t weight;
+	knot_mm_t mm;
+};
+
+/*! \brief Make the root node empty (debug-only). */
+static inline void empty_root(node_t *root) {
+#ifndef NDEBUG
+	*root = (node_t){ .branch = {
+		.flags = 3, // invalid value that fits
+		.bitmap = 0,
+		.index = -1,
+		.twigs = NULL
+	} };
+#endif
+}
+
+/*! \brief Check that unportable code works OK (debug-only). */
+static void assert_portability(void) {
+#if FLAGS_HACK
+	assert(((union node){ .leaf = {
+			.key = (tkey_t *)(((uint8_t *)NULL) + 1),
+			.val = NULL
+		} }).branch.flags == 1);
+#endif
+}
+
+/*! \brief Propagate error codes. */
+#define ERR_RETURN(x) \
+	do { \
+		int err_code_ = x; \
+		if (unlikely(err_code_ != KNOT_EOK)) \
+			return err_code_; \
+	} while (false)
+
+/*!
+ * \brief Count the number of set bits.
+ *
+ * \TODO This implementation may be relatively slow on some HW.
+ */
+static uint bitmap_weight(bitmap_t w)
+{
+	assert((w & ~((1 << 17) - 1)) == 0); // using the least-important 17 bits
+	return __builtin_popcount(w);
+}
+
+/*! \brief Only keep the lowest bit in the bitmap (least significant -> twigs[0]). */
+static bitmap_t bitmap_lowest_bit(bitmap_t w)
+{
+	assert((w & ~((1 << 17) - 1)) == 0); // using the least-important 17 bits
+	return 1 << __builtin_ctz(w);
+}
+
+/*! \brief Test flags to determine type of this node. */
+static bool isbranch(const node_t *t)
+{
+	uint f = t->branch.flags;
+	assert(f <= 2);
+	return f != 0;
+}
+
+/*! \brief Make a bitmask for testing a branch bitmap. */
+static bitmap_t nibbit(byte k, uint flags)
+{
+	uint shift = (2 - flags) << 2;
+	uint nibble = (k >> shift) & 0xf;
+	return 1 << (nibble + 1/*because of prefix keys*/);
+}
+
+/*! \brief Extract a nibble from a key and turn it into a bitmask. */
+static bitmap_t twigbit(const node_t *t, const char *key, uint32_t len)
+{
+	assert(isbranch(t));
+	uint i = t->branch.index;
+
+	if (i >= len)
+		return 1 << 0; // leaf position
+
+	return nibbit((byte)key[i], t->branch.flags);
+}
+
+/*! \brief Test if a branch node has a child indicated by a bitmask. */
+static bool hastwig(const node_t *t, bitmap_t bit)
+{
+	assert(isbranch(t));
+	return t->branch.bitmap & bit;
+}
+
+/*! \brief Compute offset of an existing child in a branch node. */
+static uint twigoff(const node_t *t, bitmap_t b)
+{
+	assert(isbranch(t));
+	return bitmap_weight(t->branch.bitmap & (b - 1));
+}
+
+/*! \brief Get pointer to a particular child of a branch node. */
+static node_t* twig(node_t *t, uint i)
+{
+	assert(isbranch(t));
+	return &t->branch.twigs[i];
+}
+
+/*!
+ * \brief For a branch nod, compute offset of a child and child count.
+ *
+ * Having this separate might be meaningful for performance optimization.
+ */
+#define TWIGOFFMAX(off, max, t, b) do {			\
+		off = twigoff(t, b);			\
+		max = bitmap_weight(t->branch.bitmap);	\
+	} while(0)
+
+/*! \brief Simple string comparator. */
+static int key_cmp(const char *k1, uint32_t k1_len, const char *k2, uint32_t k2_len)
+{
+	int ret = memcmp(k1, k2, MIN(k1_len, k2_len));
+	if (ret != 0) {
+		return ret;
+	}
+
+	/* Key string is equal, compare lengths. */
+	if (k1_len == k2_len) {
+		return 0;
+	} else if (k1_len < k2_len) {
+		return -1;
+	} else {
+		return 1;
+	}
+}
+
+trie_t* trie_create(knot_mm_t *mm)
+{
+	assert_portability();
+	trie_t *trie = mm_alloc(mm, sizeof(trie_t));
+	if (trie != NULL) {
+		empty_root(&trie->root);
+		trie->weight = 0;
+		if (mm != NULL)
+			trie->mm = *mm;
+		else
+			mm_ctx_init(&trie->mm);
+	}
+	return trie;
+}
+
+/*! \brief Free anything under the trie node, except for the passed pointer itself. */
+static void clear_trie(node_t *trie, knot_mm_t *mm)
+{
+	if (!isbranch(trie)) {
+		mm_free(mm, trie->leaf.key);
+	} else {
+		branch_t *b = &trie->branch;
+		int len = bitmap_weight(b->bitmap);
+		for (int i = 0; i < len; ++i)
+			clear_trie(b->twigs + i, mm);
+		mm_free(mm, b->twigs);
+	}
+}
+
+void trie_free(trie_t *tbl)
+{
+	if (tbl == NULL)
+		return;
+	if (tbl->weight)
+		clear_trie(&tbl->root, &tbl->mm);
+	mm_free(&tbl->mm, tbl);
+}
+
+void trie_clear(trie_t *tbl)
+{
+	assert(tbl);
+	if (!tbl->weight)
+		return;
+	clear_trie(&tbl->root, &tbl->mm);
+	empty_root(&tbl->root);
+	tbl->weight = 0;
+}
+
+size_t trie_weight(const trie_t *tbl)
+{
+	assert(tbl);
+	return tbl->weight;
+}
+
+struct found {
+	leaf_t *l;	/**< the found leaf (NULL if not found) */
+	branch_t *p;	/**< the leaf's parent (if exists) */
+	bitmap_t b;	/**< bit-mask with a single bit marking l under p */
+};
+/** Search trie for an item with the given key (equality only). */
+static struct found find_equal(trie_t *tbl, const char *key, uint32_t len)
+{
+	assert(tbl);
+	struct found ret0;
+	memset(&ret0, 0, sizeof(ret0));
+	if (!tbl->weight)
+		return ret0;
+	/* Current node and parent while descending (returned values basically). */
+	node_t *t = &tbl->root;
+	branch_t *p = NULL;
+	bitmap_t b = 0;
+	while (isbranch(t)) {
+		__builtin_prefetch(t->branch.twigs);
+		b = twigbit(t, key, len);
+		if (!hastwig(t, b))
+			return ret0;
+		p = &t->branch;
+		t = twig(t, twigoff(t, b));
+	}
+	if (key_cmp(key, len, t->leaf.key->chars, t->leaf.key->len) != 0)
+		return ret0;
+	return (struct found) {
+		.l = &t->leaf,
+		.p = p,
+		.b = b,
+	};
+}
+/** Find item with the first key (lexicographical order). */
+static struct found find_first(trie_t *tbl)
+{
+	assert(tbl);
+	if (!tbl->weight) {
+		struct found ret0;
+		memset(&ret0, 0, sizeof(ret0));
+		return ret0;
+	}
+	/* Current node and parent while descending (returned values basically). */
+	node_t *t = &tbl->root;
+	branch_t *p = NULL;
+	while (isbranch(t)) {
+		p = &t->branch;
+		t = &p->twigs[0];
+	}
+	return (struct found) {
+		.l = &t->leaf,
+		.p = p,
+		.b = p ? bitmap_lowest_bit(p->bitmap) : 0,
+	};
+}
+
+trie_val_t* trie_get_try(trie_t *tbl, const char *key, uint32_t len)
+{
+	struct found found = find_equal(tbl, key, len);
+	return found.l ? &found.l->val : NULL;
+}
+
+trie_val_t* trie_get_first(trie_t *tbl, char **key, uint32_t *len)
+{
+	struct found found = find_first(tbl);
+	if (!found.l)
+		return NULL;
+	if (key)
+		*key = found.l->key->chars;
+	if (len)
+		*len = found.l->key->len;
+	return &found.l->val;
+}
+
+/** Delete the found element (if any) and return value (unless NULL is passed) */
+static int del_found(trie_t *tbl, struct found found, trie_val_t *val)
+{
+	if (!found.l)
+		return KNOT_ENOENT;
+	mm_free(&tbl->mm, found.l->key);
+	if (val != NULL)
+		*val = found.l->val; // we return trie_val_t directly when deleting
+	--tbl->weight;
+	branch_t * const p = found.p; // short-hand
+	if (unlikely(!p)) { // whole trie was a single leaf
+		assert(tbl->weight == 0);
+		empty_root(&tbl->root);
+		return KNOT_EOK;
+	}
+	// remove leaf t as child of p; get child index via pointer arithmetic
+	int ci = ((union node *)found.l) - p->twigs,
+	    cc = bitmap_weight(p->bitmap); // child count
+	assert(ci >= 0 && ci < cc);
+
+	if (cc == 2) { // collapse binary node p: move the other child to this node
+		node_t *twigs = p->twigs;
+		(*(union node *)p) = twigs[1 - ci]; // it might be a leaf or branch
+		mm_free(&tbl->mm, twigs);
+		return KNOT_EOK;
+	}
+	memmove(p->twigs + ci, p->twigs + ci + 1, sizeof(node_t) * (cc - ci - 1));
+	p->bitmap &= ~found.b;
+	node_t *twigs = mm_realloc(&tbl->mm, p->twigs, sizeof(node_t) * (cc - 1),
+	                           sizeof(node_t) * cc);
+	if (likely(twigs != NULL))
+		p->twigs = twigs;
+		/* We can ignore mm_realloc failure, only beware that next time
+		 * the prev_size passed to it wouldn't be correct; TODO? */
+	return KNOT_EOK;
+}
+
+int trie_del(trie_t *tbl, const char *key, uint32_t len, trie_val_t *val)
+{
+	struct found found = find_equal(tbl, key, len);
+	return del_found(tbl, found, val);
+}
+
+int trie_del_first(trie_t *tbl, char *key, uint32_t *len, trie_val_t *val)
+{
+	struct found found = find_first(tbl);
+	if (!found.l)
+		return KNOT_ENOENT;
+	if (key) {
+		if (!len)
+			return KNOT_EINVAL;
+		if (*len < found.l->key->len)
+			return kr_error(ENOSPC);
+		memcpy(key, found.l->key->chars, found.l->key->len);
+	}
+	if (len) { // makes sense even with key == NULL
+		*len = found.l->key->len;
+	}
+	return del_found(tbl, found, val);
+}
+
+/*!
+ * \brief Stack of nodes, storing a path down a trie.
+ *
+ * The structure also serves directly as the public trie_it_t type,
+ * in which case it always points to the current leaf, unless we've finished
+ * (i.e. it->len == 0).
+ */
+typedef struct trie_it {
+	node_t* *stack; /*!< The stack; malloc is used directly instead of mm. */
+	uint32_t len;   /*!< Current length of the stack. */
+	uint32_t alen;  /*!< Allocated/available length of the stack. */
+	/*! \brief Initial storage for \a stack; it should fit in many use cases. */
+	node_t* stack_init[60];
+} nstack_t;
+
+/*! \brief Create a node stack containing just the root (or empty). */
+static void ns_init(nstack_t *ns, trie_t *tbl)
+{
+	assert(tbl);
+	ns->stack = ns->stack_init;
+	ns->alen = sizeof(ns->stack_init) / sizeof(ns->stack_init[0]);
+	if (tbl->weight) {
+		ns->len = 1;
+		ns->stack[0] = &tbl->root;
+	} else {
+		ns->len = 0;
+	}
+}
+
+/*! \brief Free inside of the stack, i.e. not the passed pointer itself. */
+static void ns_cleanup(nstack_t *ns)
+{
+	assert(ns && ns->stack);
+	if (likely(ns->stack == ns->stack_init))
+		return;
+	free(ns->stack);
+	#ifndef NDEBUG
+		ns->stack = NULL;
+		ns->alen = 0;
+	#endif
+}
+
+/*! \brief Allocate more space for the stack. */
+static int ns_longer_alloc(nstack_t *ns)
+{
+	ns->alen *= 2;
+	size_t new_size = sizeof(nstack_t) + ns->alen * sizeof(node_t *);
+	node_t **st;
+	if (ns->stack == ns->stack_init) {
+		st = malloc(new_size);
+		if (st != NULL)
+			memcpy(st, ns->stack, ns->len * sizeof(node_t *));
+	} else {
+		st = realloc(ns->stack, new_size);
+	}
+	if (st == NULL)
+		return KNOT_ENOMEM;
+	ns->stack = st;
+	return KNOT_EOK;
+}
+
+/*! \brief Ensure the node stack can be extended by one. */
+static inline int ns_longer(nstack_t *ns)
+{
+	// get a longer stack if needed
+	if (likely(ns->len < ns->alen))
+		return KNOT_EOK;
+	return ns_longer_alloc(ns); // hand-split the part suitable for inlining
+}
+
+/*!
+ * \brief Find the "branching point" as if searching for a key.
+ *
+ *  The whole path to the point is kept on the passed stack;
+ *  always at least the root will remain on the top of it.
+ *  Beware: the precise semantics of this function is rather tricky.
+ *  The top of the stack will contain: the corresponding leaf if exact match is found;
+ *  or the immediate node below a branching-point-on-edge or the branching-point itself.
+ *
+ *  \param info   Set position of the point of first mismatch (in index and flags).
+ *  \param first  Set the value of the first non-matching character (from trie),
+ *                optionally; end-of-string character has value -256 (that's why it's int).
+ *                Note: the character is converted to *unsigned* char (i.e. 0..255),
+ *                as that's the ordering used in the trie.
+ *
+ *  \return KNOT_EOK or KNOT_ENOMEM.
+ */
+static int ns_find_branch(nstack_t *ns, const char *key, uint32_t len,
+                          branch_t *info, int *first)
+{
+	assert(ns && ns->len && info);
+	// First find some leaf with longest matching prefix.
+	while (isbranch(ns->stack[ns->len - 1])) {
+		ERR_RETURN(ns_longer(ns));
+		node_t *t = ns->stack[ns->len - 1];
+		__builtin_prefetch(t->branch.twigs);
+		bitmap_t b = twigbit(t, key, len);
+		// Even if our key is missing from this branch we need to
+		// keep iterating down to a leaf. It doesn't matter which
+		// twig we choose since the keys are all the same up to this
+		// index. Note that blindly using twigoff(t, b) can cause
+		// an out-of-bounds index if it equals twigmax(t).
+		uint i = hastwig(t, b) ? twigoff(t, b) : 0;
+		ns->stack[ns->len++] = twig(t, i);
+	}
+	tkey_t *lkey = ns->stack[ns->len-1]->leaf.key;
+	// Find index of the first char that differs.
+	uint32_t index = 0;
+	while (index < MIN(len,lkey->len)) {
+		if (key[index] != lkey->chars[index])
+			break;
+		else
+			++index;
+	}
+	info->index = index;
+	if (first)
+		*first = lkey->len > index ? (unsigned char)lkey->chars[index] : -256;
+	// Find flags: which half-byte has matched.
+	uint flags;
+	if (index == len && len == lkey->len) { // found equivalent key
+		info->flags = flags = 0;
+		goto success;
+	}
+	if (likely(index < MIN(len,lkey->len))) {
+		byte k2 = (byte)lkey->chars[index];
+		byte k1 = (byte)key[index];
+		flags = ((k1 ^ k2) & 0xf0) ? 1 : 2;
+	} else { // one is prefix of another
+		flags = 1;
+	}
+	info->flags = flags;
+	// now go up the trie from the current leaf
+	branch_t *t;
+	do {
+		if (unlikely(ns->len == 1))
+			goto success; // only the root stays on the stack
+		t = (branch_t*)ns->stack[ns->len - 2];
+		if (t->index < index || (t->index == index && t->flags < flags))
+			goto success;
+		--ns->len;
+	} while (true);
+success:
+	#ifndef NDEBUG // invariants on successful return
+		assert(ns->len);
+		if (isbranch(ns->stack[ns->len - 1])) {
+			t = &ns->stack[ns->len - 1]->branch;
+			assert(t->index > index || (t->index == index && t->flags >= flags));
+		}
+		if (ns->len > 1) {
+			t = &ns->stack[ns->len - 2]->branch;
+			assert(t->index < index || (t->index == index
+			       && (t->flags < flags || (t->flags == 1 && flags == 0))));
+		}
+	#endif
+	return KNOT_EOK;
+}
+
+/*!
+ * \brief Advance the node stack to the last leaf in the subtree.
+ *
+ * \return KNOT_EOK or KNOT_ENOMEM.
+ */
+static int ns_last_leaf(nstack_t *ns)
+{
+	assert(ns);
+	do {
+		ERR_RETURN(ns_longer(ns));
+		node_t *t = ns->stack[ns->len - 1];
+		if (!isbranch(t))
+			return KNOT_EOK;
+		int lasti = bitmap_weight(t->branch.bitmap) - 1;
+		assert(lasti >= 0);
+		ns->stack[ns->len++] = twig(t, lasti);
+	} while (true);
+}
+
+/*!
+ * \brief Advance the node stack to the first leaf in the subtree.
+ *
+ * \return KNOT_EOK or KNOT_ENOMEM.
+ */
+static int ns_first_leaf(nstack_t *ns)
+{
+	assert(ns && ns->len);
+	do {
+		ERR_RETURN(ns_longer(ns));
+		node_t *t = ns->stack[ns->len - 1];
+		if (!isbranch(t))
+			return KNOT_EOK;
+		ns->stack[ns->len++] = twig(t, 0);
+	} while (true);
+}
+
+/*!
+ * \brief Advance the node stack to the leaf that is previous to the current node.
+ *
+ * \note Prefix leaf under the current node DOES count (if present; perhaps questionable).
+ * \return KNOT_EOK on success, KNOT_ENOENT on not-found, or possibly KNOT_ENOMEM.
+ */
+static int ns_prev_leaf(nstack_t *ns)
+{
+	assert(ns && ns->len > 0);
+
+	node_t *t = ns->stack[ns->len - 1];
+	if (hastwig(t, 1 << 0)) { // the prefix leaf
+		t = twig(t, 0);
+		ERR_RETURN(ns_longer(ns));
+		ns->stack[ns->len++] = t;
+		return KNOT_EOK;
+	}
+
+	do {
+		if (ns->len < 2)
+			return KNOT_ENOENT; // root without empty key has no previous leaf
+		t = ns->stack[ns->len - 1];
+		node_t *p = ns->stack[ns->len - 2];
+		int pindex = t - p->branch.twigs; // index in parent via pointer arithmetic
+		assert(pindex >= 0 && pindex <= 16);
+		if (pindex > 0) { // t isn't the first child -> go down the previous one
+			ns->stack[ns->len - 1] = twig(p, pindex - 1);
+			return ns_last_leaf(ns);
+		}
+		// we've got to go up again
+		--ns->len;
+	} while (true);
+}
+
+/*!
+ * \brief Advance the node stack to the leaf that is successor to the current node.
+ *
+ * \note Prefix leaf or anything else under the current node DOES count.
+ * \return KNOT_EOK on success, KNOT_ENOENT on not-found, or possibly KNOT_ENOMEM.
+ */
+static int ns_next_leaf(nstack_t *ns)
+{
+	assert(ns && ns->len > 0);
+
+	node_t *t = ns->stack[ns->len - 1];
+	if (isbranch(t))
+		return ns_first_leaf(ns);
+	do {
+		if (ns->len < 2)
+			return KNOT_ENOENT; // not found, as no more parent is available
+		t = ns->stack[ns->len - 1];
+		node_t *p = ns->stack[ns->len - 2];
+		int pindex = t - p->branch.twigs; // index in parent via pointer arithmetic
+		assert(pindex >= 0 && pindex <= 16);
+		int pcount = bitmap_weight(p->branch.bitmap);
+		if (pindex + 1 < pcount) { // t isn't the last child -> go down the next one
+			ns->stack[ns->len - 1] = twig(p, pindex + 1);
+			return ns_first_leaf(ns);
+		}
+		// we've got to go up again
+		--ns->len;
+	} while (true);
+}
+
+int trie_get_leq(trie_t *tbl, const char *key, uint32_t len, trie_val_t **val)
+{
+	assert(tbl && val);
+	*val = NULL; // so on failure we can just return;
+	if (tbl->weight == 0)
+		return KNOT_ENOENT;
+	{ // Intentionally un-indented; until end of function, to bound cleanup attr.
+	// First find a key with longest-matching prefix
+	__attribute__((cleanup(ns_cleanup)))
+		nstack_t ns_local;
+	ns_init(&ns_local, tbl);
+	nstack_t *ns = &ns_local;
+	branch_t bp;
+	int un_leaf; // first unmatched character in the leaf
+	ERR_RETURN(ns_find_branch(ns, key, len, &bp, &un_leaf));
+	int un_key = bp.index < len ? (unsigned char)key[bp.index] : -256;
+	node_t *t = ns->stack[ns->len - 1];
+	if (bp.flags == 0) { // found exact match
+		*val = &t->leaf.val;
+		return KNOT_EOK;
+	}
+	// Get t: the last node on matching path
+	if (isbranch(t) && t->branch.index == bp.index && t->branch.flags == bp.flags) {
+		// t is OK
+	} else {
+		// the top of the stack was the first unmatched node -> step up
+		if (ns->len == 1) {
+			// root was unmatched already
+			if (un_key < un_leaf)
+				return KNOT_ENOENT;
+			ERR_RETURN(ns_last_leaf(ns));
+			goto success;
+		}
+		--ns->len;
+		t = ns->stack[ns->len - 1];
+	}
+	// Now we re-do the first "non-matching" step in the trie
+	// but try the previous child if key was less (it may not exist)
+	bitmap_t b = twigbit(t, key, len);
+	int i = hastwig(t, b)
+		? twigoff(t, b) - (un_key < un_leaf)
+		: twigoff(t, b) - 1 /*twigoff returns successor when !hastwig*/;
+	if (i >= 0) {
+		ERR_RETURN(ns_longer(ns));
+		ns->stack[ns->len++] = twig(t, i);
+		ERR_RETURN(ns_last_leaf(ns));
+	} else {
+		ERR_RETURN(ns_prev_leaf(ns));
+	}
+success:
+	assert(!isbranch(ns->stack[ns->len - 1]));
+	*val = &ns->stack[ns->len - 1]->leaf.val;
+	return 1;
+	}
+}
+
+/*! \brief Initialize a new leaf, copying the key, and returning failure code. */
+static int mk_leaf(node_t *leaf, const char *key, uint32_t len, knot_mm_t *mm)
+{
+	tkey_t *k = mm_alloc(mm, sizeof(tkey_t) + len);
+	#if FLAGS_HACK
+		assert(((uintptr_t)k) % 4 == 0); // we need an aligned pointer
+	#endif
+	if (unlikely(!k))
+		return KNOT_ENOMEM;
+	k->len = len;
+	memcpy(k->chars, key, len);
+	leaf->leaf = (leaf_t){
+		#if !FLAGS_HACK
+			.flags = 0,
+		#endif
+		.val = NULL,
+		.key = k
+	};
+	return KNOT_EOK;
+}
+
+trie_val_t* trie_get_ins(trie_t *tbl, const char *key, uint32_t len)
+{
+	assert(tbl);
+	// First leaf in an empty tbl?
+	if (unlikely(!tbl->weight)) {
+		if (unlikely(mk_leaf(&tbl->root, key, len, &tbl->mm)))
+			return NULL;
+		++tbl->weight;
+		return &tbl->root.leaf.val;
+	}
+	{ // Intentionally un-indented; until end of function, to bound cleanup attr.
+	// Find the branching-point
+	__attribute__((cleanup(ns_cleanup)))
+		nstack_t ns_local;
+	ns_init(&ns_local, tbl);
+	nstack_t *ns = &ns_local;
+	branch_t bp; // branch-point: index and flags signifying the longest common prefix
+	int k2; // the first unmatched character in the leaf
+	if (unlikely(ns_find_branch(ns, key, len, &bp, &k2)))
+		return NULL;
+	node_t *t = ns->stack[ns->len - 1];
+	if (bp.flags == 0) // the same key was already present
+		return &t->leaf.val;
+	node_t leaf;
+	if (unlikely(mk_leaf(&leaf, key, len, &tbl->mm)))
+		return NULL;
+
+	if (isbranch(t) && bp.index == t->branch.index && bp.flags == t->branch.flags) {
+		// The node t needs a new leaf child.
+		bitmap_t b1 = twigbit(t, key, len);
+		assert(!hastwig(t, b1));
+		uint s, m; TWIGOFFMAX(s, m, t, b1); // new child position and original child count
+		node_t *twigs = mm_realloc(&tbl->mm, t->branch.twigs,
+				sizeof(node_t) * (m + 1), sizeof(node_t) * m);
+		if (unlikely(!twigs))
+			goto err_leaf;
+		memmove(twigs + s + 1, twigs + s, sizeof(node_t) * (m - s));
+		twigs[s] = leaf;
+		t->branch.twigs = twigs;
+		t->branch.bitmap |= b1;
+		++tbl->weight;
+		return &twigs[s].leaf.val;
+	} else {
+		// We need to insert a new binary branch with leaf at *t.
+		// Note: it works the same for the case where we insert above root t.
+		#ifndef NDEBUG
+			if (ns->len > 1) {
+				node_t *pt = ns->stack[ns->len - 2];
+				assert(hastwig(pt, twigbit(pt, key, len)));
+			}
+		#endif
+		node_t *twigs = mm_alloc(&tbl->mm, sizeof(node_t) * 2);
+		if (unlikely(!twigs))
+			goto err_leaf;
+		node_t t2 = *t; // Save before overwriting t.
+		t->branch.flags = bp.flags;
+		t->branch.index = bp.index;
+		t->branch.twigs = twigs;
+		bitmap_t b1 = twigbit(t, key, len);
+		bitmap_t b2 = unlikely(k2 == -256) ? (1 << 0) : nibbit(k2, bp.flags);
+		t->branch.bitmap = b1 | b2;
+		*twig(t, twigoff(t, b1)) = leaf;
+		*twig(t, twigoff(t, b2)) = t2;
+		++tbl->weight;
+		return &twig(t, twigoff(t, b1))->leaf.val;
+	};
+err_leaf:
+	mm_free(&tbl->mm, leaf.leaf.key);
+	return NULL;
+	}
+}
+
+/*! \brief Apply a function to every trie_val_t*, in order; a recursive solution. */
+static int apply_trie(node_t *t, int (*f)(trie_val_t *, void *), void *d)
+{
+	assert(t);
+	if (!isbranch(t))
+		return f(&t->leaf.val, d);
+	int child_count = bitmap_weight(t->branch.bitmap);
+	for (int i = 0; i < child_count; ++i)
+		ERR_RETURN(apply_trie(twig(t, i), f, d));
+	return KNOT_EOK;
+}
+
+int trie_apply(trie_t *tbl, int (*f)(trie_val_t *, void *), void *d)
+{
+	assert(tbl && f);
+	if (!tbl->weight)
+		return KNOT_EOK;
+	return apply_trie(&tbl->root, f, d);
+}
+
+/* These are all thin wrappers around static Tns* functions. */
+trie_it_t* trie_it_begin(trie_t *tbl)
+{
+	assert(tbl);
+	trie_it_t *it = malloc(sizeof(nstack_t));
+	if (!it)
+		return NULL;
+	ns_init(it, tbl);
+	if (it->len == 0) // empty tbl
+		return it;
+	if (ns_first_leaf(it)) {
+		ns_cleanup(it);
+		free(it);
+		return NULL;
+	}
+	return it;
+}
+
+void trie_it_next(trie_it_t *it)
+{
+	assert(it && it->len);
+	if (ns_next_leaf(it) != KNOT_EOK)
+		it->len = 0;
+}
+
+bool trie_it_finished(trie_it_t *it)
+{
+	assert(it);
+	return it->len == 0;
+}
+
+void trie_it_free(trie_it_t *it)
+{
+	if (!it)
+		return;
+	ns_cleanup(it);
+	free(it);
+}
+
+const char* trie_it_key(trie_it_t *it, size_t *len)
+{
+	assert(it && it->len);
+	node_t *t = it->stack[it->len - 1];
+	assert(!isbranch(t));
+	tkey_t *key = t->leaf.key;
+	if (len)
+		*len = key->len;
+	return key->chars;
+}
+
+trie_val_t* trie_it_val(trie_it_t *it)
+{
+	assert(it && it->len);
+	node_t *t = it->stack[it->len - 1];
+	assert(!isbranch(t));
+	return &t->leaf.val;
+}