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diff --git a/trie.c b/trie.c
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-/****************************************************************************
- * bfs                                                                      *
- * Copyright (C) 2019 Tavian Barnes <tavianator@tavianator.com>             *
- *                                                                          *
- * Permission to use, copy, modify, and/or distribute this software for any *
- * purpose with or without fee is hereby granted.                           *
- *                                                                          *
- * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES *
- * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF         *
- * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR  *
- * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES   *
- * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN    *
- * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF  *
- * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.           *
- ****************************************************************************/
-
-/**
- * This is an implementation of a "qp trie," as documented at
- * https://dotat.at/prog/qp/README.html
- *
- * An uncompressed trie over the dataset {AAAA, AADD, ABCD, DDAA, DDDD} would
- * look like
- *
- *       A    A    A    A
- *     *--->*--->*--->*--->$
- *     |    |    | D    D
- *     |    |    +--->*--->$
- *     |    | B    C    D
- *     |    +--->*--->*--->$
- *     | D    D    A    A
- *     +--->*--->*--->*--->$
- *               | D    D
- *               +--->*--->$
- *
- * A compressed (PATRICIA) trie collapses internal nodes that have only a single
- * child, like this:
- *
- *       A    A    AA
- *     *--->*--->*---->$
- *     |    |    | DD
- *     |    |    +---->$
- *     |    | BCD
- *     |    +----->$
- *     | DD    AA
- *     +---->*---->$
- *           | DD
- *           +---->$
- *
- * The nodes can be compressed further by dropping the actual compressed
- * sequences from the nodes, storing it only in the leaves.  This is the
- * technique applied in QP tries, and the crit-bit trees that inspired them
- * (https://cr.yp.to/critbit.html).  Only the index to test, and the values to
- * branch on, need to be stored in each node.
- *
- *       A    A    A
- *     0--->1--->2--->AAAA
- *     |    |    | D
- *     |    |    +--->AADD
- *     |    | B
- *     |    +--->ABCD
- *     | D    A
- *     +--->2--->DDAA
- *          | D
- *          +--->DDDD
- *
- * Nodes are represented very compactly.  Rather than a dense array of children,
- * a sparse array of only the non-NULL children directly follows the node in
- * memory.  A bitmap is used to track which children exist; the index of a child
- * i is found by counting the number of bits below bit i that are set.  A tag
- * bit is used to tell pointers to internal nodes apart from pointers to leaves.
- *
- * This implementation tests a whole nibble (half byte/hex digit) at every
- * branch, so the bitmap takes up 16 bits.  The remainder of a machine word is
- * used to hold the offset, which severely constrains its range on 32-bit
- * platforms.  As a workaround, we store relative instead of absolute offsets,
- * and insert intermediate singleton "jump" nodes when necessary.
- */
-
-#include "trie.h"
-#include <assert.h>
-#include <limits.h>
-#include <stdbool.h>
-#include <stdint.h>
-#include <stdlib.h>
-#include <string.h>
-
-#if CHAR_BIT != 8
-#	error "This trie implementation assumes 8-bit bytes."
-#endif
-
-/** Number of bits for the sparse array bitmap, aka the range of a nibble. */
-#define BITMAP_BITS 16
-/** The number of remaining bits in a word, to hold the offset. */
-#define OFFSET_BITS (sizeof(size_t)*CHAR_BIT - BITMAP_BITS)
-/** The highest representable offset (only 64k on a 32-bit architecture). */
-#define OFFSET_MAX (((size_t)1 << OFFSET_BITS) - 1)
-
-/**
- * An internal node of the trie.
- */
-struct trie_node {
-	/**
-	 * A bitmap that hold which indices exist in the sparse children array.
-	 * Bit i will be set if a child exists at logical index i, and its index
-	 * into the array will be popcount(bitmap & ((1 << i) - 1)).
-	 */
-	size_t bitmap : BITMAP_BITS;
-
-	/**
-	 * The offset into the key in nibbles.  This is relative to the parent
-	 * node, to support offsets larger than OFFSET_MAX.
-	 */
-	size_t offset : OFFSET_BITS;
-
-	/**
-	 * Flexible array of children.  Each pointer uses the lowest bit as a
-	 * tag to distinguish internal nodes from leaves.  This is safe as long
-	 * as all dynamic allocations are aligned to more than a single byte.
-	 */
-	uintptr_t children[];
-};
-
-/** Check if an encoded pointer is to a leaf. */
-static bool trie_is_leaf(uintptr_t ptr) {
-	return ptr & 1;
-}
-
-/** Decode a pointer to a leaf. */
-static struct trie_leaf *trie_decode_leaf(uintptr_t ptr) {
-	assert(trie_is_leaf(ptr));
-	return (struct trie_leaf *)(ptr ^ 1);
-}
-
-/** Encode a pointer to a leaf. */
-static uintptr_t trie_encode_leaf(const struct trie_leaf *leaf) {
-	uintptr_t ptr = (uintptr_t)leaf ^ 1;
-	assert(trie_is_leaf(ptr));
-	return ptr;
-}
-
-/** Decode a pointer to an internal node. */
-static struct trie_node *trie_decode_node(uintptr_t ptr) {
-	assert(!trie_is_leaf(ptr));
-	return (struct trie_node *)ptr;
-}
-
-/** Encode a pointer to an internal node. */
-static uintptr_t trie_encode_node(const struct trie_node *node) {
-	uintptr_t ptr = (uintptr_t)node;
-	assert(!trie_is_leaf(ptr));
-	return ptr;
-}
-
-void trie_init(struct trie *trie) {
-	trie->root = 0;
-}
-
-/** Compute the popcount (Hamming weight) of a bitmap. */
-static unsigned int trie_popcount(unsigned int n) {
-#if __POPCNT__
-	// Use the x86 instruction if we have it.  Otherwise, GCC generates a
-	// library call, so use the below implementation instead.
-	return __builtin_popcount(n);
-#else
-	// See https://en.wikipedia.org/wiki/Hamming_weight#Efficient_implementation
-	n -= (n >> 1) & 0x5555;
-	n = (n & 0x3333) + ((n >> 2) & 0x3333);
-	n = (n + (n >> 4)) & 0x0F0F;
-	n = (n + (n >> 8)) & 0xFF;
-	return n;
-#endif
-}
-
-/** Extract the nibble at a certain offset from a byte sequence. */
-static unsigned char trie_key_nibble(const void *key, size_t offset) {
-	const unsigned char *bytes = key;
-	size_t byte = offset >> 1;
-
-	// A branchless version of
-	// if (offset & 1) {
-	//         return bytes[byte] >> 4;
-	// } else {
-	//         return bytes[byte] & 0xF;
-	// }
-	unsigned int shift = (offset & 1) << 2;
-	return (bytes[byte] >> shift) & 0xF;
-}
-
-/**
- * Finds a leaf in the trie that matches the key at every branch.  If the key
- * exists in the trie, the representative will match the searched key.  But
- * since only branch points are tested, it can be different from the key.  In
- * that case, the first mismatch between the key and the representative will be
- * the depth at which to make a new branch to insert the key.
- */
-static struct trie_leaf *trie_representative(const struct trie *trie, const void *key, size_t length) {
-	uintptr_t ptr = trie->root;
-	if (!ptr) {
-		return NULL;
-	}
-
-	size_t offset = 0;
-	while (!trie_is_leaf(ptr)) {
-		struct trie_node *node = trie_decode_node(ptr);
-		offset += node->offset;
-
-		unsigned int index = 0;
-		if ((offset >> 1) < length) {
-			unsigned char nibble = trie_key_nibble(key, offset);
-			unsigned int bit = 1U << nibble;
-			if (node->bitmap & bit) {
-				index = trie_popcount(node->bitmap & (bit - 1));
-			}
-		}
-		ptr = node->children[index];
-	}
-
-	return trie_decode_leaf(ptr);
-}
-
-struct trie_leaf *trie_first_leaf(const struct trie *trie) {
-	return trie_representative(trie, NULL, 0);
-}
-
-struct trie_leaf *trie_find_str(const struct trie *trie, const char *key) {
-	return trie_find_mem(trie, key, strlen(key) + 1);
-}
-
-struct trie_leaf *trie_find_mem(const struct trie *trie, const void *key, size_t length) {
-	struct trie_leaf *rep = trie_representative(trie, key, length);
-	if (rep && rep->length == length && memcmp(rep->key, key, length) == 0) {
-		return rep;
-	} else {
-		return NULL;
-	}
-}
-
-struct trie_leaf *trie_find_postfix(const struct trie *trie, const char *key) {
-	size_t length = strlen(key);
-	struct trie_leaf *rep = trie_representative(trie, key, length + 1);
-	if (rep && rep->length >= length && memcmp(rep->key, key, length) == 0) {
-		return rep;
-	} else {
-		return NULL;
-	}
-}
-
-/**
- * Find a leaf that may end at the current node.
- */
-static struct trie_leaf *trie_terminal_leaf(const struct trie_node *node) {
-	// Finding a terminating NUL byte may take two nibbles
-	for (int i = 0; i < 2; ++i) {
-		if (!(node->bitmap & 1)) {
-			break;
-		}
-
-		uintptr_t ptr = node->children[0];
-		if (trie_is_leaf(ptr)) {
-			return trie_decode_leaf(ptr);
-		} else {
-			node = trie_decode_node(ptr);
-		}
-	}
-
-	return NULL;
-}
-
-/** Check if a leaf is a prefix of a search key. */
-static bool trie_check_prefix(struct trie_leaf *leaf, size_t skip, const char *key, size_t length) {
-	if (leaf && leaf->length <= length) {
-		return memcmp(key + skip, leaf->key + skip, leaf->length - skip - 1) == 0;
-	} else {
-		return false;
-	}
-}
-
-struct trie_leaf *trie_find_prefix(const struct trie *trie, const char *key) {
-	uintptr_t ptr = trie->root;
-	if (!ptr) {
-		return NULL;
-	}
-
-	struct trie_leaf *best = NULL;
-	size_t skip = 0;
-	size_t length = strlen(key) + 1;
-
-	size_t offset = 0;
-	while (!trie_is_leaf(ptr)) {
-		struct trie_node *node = trie_decode_node(ptr);
-		offset += node->offset;
-		if ((offset >> 1) >= length) {
-			return best;
-		}
-
-		struct trie_leaf *leaf = trie_terminal_leaf(node);
-		if (trie_check_prefix(leaf, skip, key, length)) {
-			best = leaf;
-			skip = offset >> 1;
-		}
-
-		unsigned char nibble = trie_key_nibble(key, offset);
-		unsigned int bit = 1U << nibble;
-		if (node->bitmap & bit) {
-			unsigned int index = trie_popcount(node->bitmap & (bit - 1));
-			ptr = node->children[index];
-		} else {
-			return best;
-		}
-	}
-
-	struct trie_leaf *leaf = trie_decode_leaf(ptr);
-	if (trie_check_prefix(leaf, skip, key, length)) {
-		best = leaf;
-	}
-
-	return best;
-}
-
-/** Create a new leaf, holding a copy of the given key. */
-static struct trie_leaf *new_trie_leaf(const void *key, size_t length) {
-	struct trie_leaf *leaf = malloc(sizeof(*leaf) + length);
-	if (leaf) {
-		leaf->value = NULL;
-		leaf->length = length;
-		memcpy(leaf->key, key, length);
-	}
-	return leaf;
-}
-
-/** Compute the size of a trie node with a certain number of children. */
-static size_t trie_node_size(unsigned int size) {
-	// Empty nodes aren't supported
-	assert(size > 0);
-	// Node size must be a power of two
-	assert((size & (size - 1)) == 0);
-
-	return sizeof(struct trie_node) + size*sizeof(uintptr_t);
-}
-
-/** Find the offset of the first nibble that differs between two keys. */
-static size_t trie_key_mismatch(const void *key1, const void *key2, size_t length) {
-	const unsigned char *bytes1 = key1;
-	const unsigned char *bytes2 = key2;
-	size_t i = 0;
-	size_t offset = 0;
-	const size_t chunk = sizeof(size_t);
-
-	for (; i + chunk <= length; i += chunk) {
-		if (memcmp(bytes1 + i, bytes2 + i, chunk) != 0) {
-			break;
-		}
-	}
-
-	for (; i < length; ++i) {
-		unsigned char b1 = bytes1[i], b2 = bytes2[i];
-		if (b1 != b2) {
-			offset = (b1 & 0xF) == (b2 & 0xF);
-			break;
-		}
-	}
-
-	offset |= i << 1;
-	return offset;
-}
-
-/**
- * Insert a key into a node.  The node must not have a child in that position
- * already.  Effectively takes a subtrie like this:
- *
- *     ptr
- *      |
- *      v X
- *      *--->...
- *      | Z
- *      +--->...
- *
- * and transforms it to:
- *
- *     ptr
- *      |
- *      v X
- *      *--->...
- *      | Y
- *      +--->key
- *      | Z
- *      +--->...
- */
-static struct trie_leaf *trie_node_insert(uintptr_t *ptr, const void *key, size_t length, size_t offset) {
-	struct trie_node *node = trie_decode_node(*ptr);
-	unsigned int size = trie_popcount(node->bitmap);
-
-	// Double the capacity every power of two
-	if ((size & (size - 1)) == 0) {
-		node = realloc(node, trie_node_size(2*size));
-		if (!node) {
-			return NULL;
-		}
-		*ptr = trie_encode_node(node);
-	}
-
-	struct trie_leaf *leaf = new_trie_leaf(key, length);
-	if (!leaf) {
-		return NULL;
-	}
-
-	unsigned char nibble = trie_key_nibble(key, offset);
-	unsigned int bit = 1U << nibble;
-
-	// The child must not already be present
-	assert(!(node->bitmap & bit));
-	node->bitmap |= bit;
-
-	unsigned int index = trie_popcount(node->bitmap & (bit - 1));
-	uintptr_t *child = node->children + index;
-	if (index < size) {
-		memmove(child + 1, child, (size - index)*sizeof(*child));
-	}
-	*child = trie_encode_leaf(leaf);
-	return leaf;
-}
-
-/**
- * When the current offset exceeds OFFSET_MAX, insert "jump" nodes that bridge
- * the gap.  This function takes a subtrie like this:
- *
- *     ptr
- *      |
- *      v
- *      *--->rep
- *
- * and changes it to:
- *
- *     ptr  ret
- *      |    |
- *      v    v
- *      *--->*--->rep
- *
- * so that a new key can be inserted like:
- *
- *     ptr  ret
- *      |    |
- *      v    v X
- *      *--->*--->rep
- *           | Y
- *           +--->key
- */
-static uintptr_t *trie_jump(uintptr_t *ptr, const char *key, size_t *offset) {
-	// We only ever need to jump to leaf nodes, since internal nodes are
-	// guaranteed to be within OFFSET_MAX anyway
-	assert(trie_is_leaf(*ptr));
-
-	struct trie_node *node = malloc(trie_node_size(1));
-	if (!node) {
-		return NULL;
-	}
-
-	*offset += OFFSET_MAX;
-	node->offset = OFFSET_MAX;
-
-	unsigned char nibble = trie_key_nibble(key, *offset);
-	node->bitmap = 1 << nibble;
-
-	node->children[0] = *ptr;
-	*ptr = trie_encode_node(node);
-	return node->children;
-}
-
-/**
- * Split a node in the trie.  Changes a subtrie like this:
- *
- *     ptr
- *      |
- *      v
- *      *...>--->rep
- *
- * into this:
- *
- *     ptr
- *      |
- *      v X
- *      *--->*...>--->rep
- *      | Y
- *      +--->key
- */
-static struct trie_leaf *trie_split(uintptr_t *ptr, const void *key, size_t length, struct trie_leaf *rep, size_t offset, size_t mismatch) {
-	unsigned char key_nibble = trie_key_nibble(key, mismatch);
-	unsigned char rep_nibble = trie_key_nibble(rep->key, mismatch);
-	assert(key_nibble != rep_nibble);
-
-	struct trie_node *node = malloc(trie_node_size(2));
-	if (!node) {
-		return NULL;
-	}
-
-	struct trie_leaf *leaf = new_trie_leaf(key, length);
-	if (!leaf) {
-		free(node);
-		return NULL;
-	}
-
-	node->bitmap = (1 << key_nibble) | (1 << rep_nibble);
-
-	size_t delta = mismatch - offset;
-	if (!trie_is_leaf(*ptr)) {
-		struct trie_node *child = trie_decode_node(*ptr);
-		child->offset -= delta;
-	}
-	node->offset = delta;
-
-	unsigned int key_index = key_nibble > rep_nibble;
-	node->children[key_index] = trie_encode_leaf(leaf);
-	node->children[key_index ^ 1] = *ptr;
-	*ptr = trie_encode_node(node);
-	return leaf;
-}
-
-struct trie_leaf *trie_insert_str(struct trie *trie, const char *key) {
-	return trie_insert_mem(trie, key, strlen(key) + 1);
-}
-
-struct trie_leaf *trie_insert_mem(struct trie *trie, const void *key, size_t length) {
-	struct trie_leaf *rep = trie_representative(trie, key, length);
-	if (!rep) {
-		struct trie_leaf *leaf = new_trie_leaf(key, length);
-		if (leaf) {
-			trie->root = trie_encode_leaf(leaf);
-		}
-		return leaf;
-	}
-
-	size_t limit = length < rep->length ? length : rep->length;
-	size_t mismatch = trie_key_mismatch(key, rep->key, limit);
-	if ((mismatch >> 1) >= length) {
-		return rep;
-	}
-
-	size_t offset = 0;
-	uintptr_t *ptr = &trie->root;
-	while (!trie_is_leaf(*ptr)) {
-		struct trie_node *node = trie_decode_node(*ptr);
-		if (offset + node->offset > mismatch) {
-			break;
-		}
-		offset += node->offset;
-
-		unsigned char nibble = trie_key_nibble(key, offset);
-		unsigned int bit = 1U << nibble;
-		if (node->bitmap & bit) {
-			assert(offset < mismatch);
-			unsigned int index = trie_popcount(node->bitmap & (bit - 1));
-			ptr = node->children + index;
-		} else {
-			assert(offset == mismatch);
-			return trie_node_insert(ptr, key, length, offset);
-		}
-	}
-
-	while (mismatch - offset > OFFSET_MAX) {
-		ptr = trie_jump(ptr, key, &offset);
-		if (!ptr) {
-			return NULL;
-		}
-	}
-
-	return trie_split(ptr, key, length, rep, offset, mismatch);
-}
-
-/** Free a chain of singleton nodes. */
-static void trie_free_singletons(uintptr_t ptr) {
-	while (!trie_is_leaf(ptr)) {
-		struct trie_node *node = trie_decode_node(ptr);
-
-		// Make sure the bitmap is a power of two, i.e. it has just one child
-		assert((node->bitmap & (node->bitmap - 1)) == 0);
-
-		ptr = node->children[0];
-		free(node);
-	}
-
-	free(trie_decode_leaf(ptr));
-}
-
-/**
- * Try to collapse a two-child node like:
- *
- *     parent child
- *       |      |
- *       v      v
- *       *----->*----->*----->leaf
- *       |
- *       +----->other
- *
- * into
- *
- *     parent
- *       |
- *       v
- *     other
- */
-static int trie_collapse_node(uintptr_t *parent, struct trie_node *parent_node, unsigned int child_index) {
-	uintptr_t other = parent_node->children[child_index ^ 1];
-	if (!trie_is_leaf(other)) {
-		struct trie_node *other_node = trie_decode_node(other);
-		if (other_node->offset + parent_node->offset <= OFFSET_MAX) {
-			other_node->offset += parent_node->offset;
-		} else {
-			return -1;
-		}
-	}
-
-	*parent = other;
-	free(parent_node);
-	return 0;
-}
-
-void trie_remove(struct trie *trie, struct trie_leaf *leaf) {
-	uintptr_t *child = &trie->root;
-	uintptr_t *parent = NULL;
-	unsigned int child_bit = 0, child_index = 0;
-	size_t offset = 0;
-	while (!trie_is_leaf(*child)) {
-		struct trie_node *node = trie_decode_node(*child);
-		offset += node->offset;
-		assert((offset >> 1) < leaf->length);
-
-		unsigned char nibble = trie_key_nibble(leaf->key, offset);
-		unsigned int bit = 1U << nibble;
-		unsigned int bitmap = node->bitmap;
-		assert(bitmap & bit);
-		unsigned int index = trie_popcount(bitmap & (bit - 1));
-
-		// Advance the parent pointer, unless this node had only one child
-		if (bitmap & (bitmap - 1)) {
-			parent = child;
-			child_bit = bit;
-			child_index = index;
-		}
-
-		child = node->children + index;
-	}
-
-	assert(trie_decode_leaf(*child) == leaf);
-
-	if (!parent) {
-		trie_free_singletons(trie->root);
-		trie->root = 0;
-		return;
-	}
-
-	struct trie_node *node = trie_decode_node(*parent);
-	child = node->children + child_index;
-	trie_free_singletons(*child);
-
-	node->bitmap ^= child_bit;
-	unsigned int parent_size = trie_popcount(node->bitmap);
-	assert(parent_size > 0);
-	if (parent_size == 1 && trie_collapse_node(parent, node, child_index) == 0) {
-		return;
-	}
-
-	if (child_index < parent_size) {
-		memmove(child, child + 1, (parent_size - child_index)*sizeof(*child));
-	}
-
-	if ((parent_size & (parent_size - 1)) == 0) {
-		node = realloc(node, trie_node_size(parent_size));
-		if (node) {
-			*parent = trie_encode_node(node);
-		}
-	}
-}
-
-/** Free an encoded pointer to a node. */
-static void free_trie_ptr(uintptr_t ptr) {
-	if (trie_is_leaf(ptr)) {
-		free(trie_decode_leaf(ptr));
-	} else {
-		struct trie_node *node = trie_decode_node(ptr);
-		size_t size = trie_popcount(node->bitmap);
-		for (size_t i = 0; i < size; ++i) {
-			free_trie_ptr(node->children[i]);
-		}
-		free(node);
-	}
-}
-
-void trie_destroy(struct trie *trie) {
-	if (trie->root) {
-		free_trie_ptr(trie->root);
-	}
-}