Add zix data structures

9 files changed, 1839 insertions, 1 deletions

diff --git a/meson.build b/meson.build
index 1203b176..16fce995 100644
--- a/meson.build
+++ b/meson.build
@@ -59,7 +59,7 @@ if get_option('strict')
   elif cc.get_id() == 'msvc'
     c_warnings += [
       '/wd4061',  # enumerator in switch is not explicitly handled
-      '/wd4365',  # signed/unsigned mismatch
+      '/wd4200',  # nonstandard: zero-sized array in struct/union
       '/wd4514',  # unreferenced inline function has been removed
       '/wd4706',  # assignment within conditional expression
       '/wd4710',  # function not inlined
diff --git a/src/.clang-tidy b/src/.clang-tidy
index 5be37470..79f266d9 100644
--- a/src/.clang-tidy
+++ b/src/.clang-tidy
@@ -9,6 +9,7 @@ Checks: >
   -cert-dcl51-cpp,
   -clang-analyzer-security.insecureAPI.DeprecatedOrUnsafeBufferHandling,
   -google-readability-todo,
+  -hicpp-multiway-paths-covered,
   -hicpp-signed-bitwise,
   -llvm-header-guard,
   -llvmlibc-*,
diff --git a/src/zix/btree.c b/src/zix/btree.c
new file mode 100644
index 00000000..19fee858
--- /dev/null
+++ b/src/zix/btree.c
@@ -0,0 +1,936 @@
+/*
+  Copyright 2011-2020 David Robillard <d@drobilla.net>
+
+  Permission to use, copy, modify, and/or distribute this software for any
+  purpose with or without fee is hereby granted, provided that the above
+  copyright notice and this permission notice appear in all copies.
+
+  THIS 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.
+*/
+
+#include "zix/btree.h"
+
+#include <assert.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <string.h>
+
+// #define ZIX_BTREE_DEBUG 1
+// #define ZIX_BTREE_SORTED_CHECK 1
+
+#ifndef ZIX_BTREE_PAGE_SIZE
+#  define ZIX_BTREE_PAGE_SIZE 4096
+#endif
+
+#define ZIX_BTREE_NODE_SPACE (ZIX_BTREE_PAGE_SIZE - 2 * sizeof(uint16_t))
+#define ZIX_BTREE_LEAF_VALS ((ZIX_BTREE_NODE_SPACE / sizeof(void*)) - 1)
+#define ZIX_BTREE_INODE_VALS (ZIX_BTREE_LEAF_VALS / 2)
+
+struct ZixBTreeImpl {
+  ZixBTreeNode*  root;
+  ZixDestroyFunc destroy;
+  ZixComparator  cmp;
+  const void*    cmp_data;
+  size_t         size;
+  unsigned       height; ///< Number of levels, i.e. root only has height 1
+};
+
+struct ZixBTreeNodeImpl {
+  uint16_t is_leaf;
+  uint16_t n_vals;
+  // On 64-bit we rely on some padding here to get page-sized nodes
+  union {
+    struct {
+      void* vals[ZIX_BTREE_LEAF_VALS];
+    } leaf;
+
+    struct {
+      void*         vals[ZIX_BTREE_INODE_VALS];
+      ZixBTreeNode* children[ZIX_BTREE_INODE_VALS + 1];
+    } inode;
+  } data;
+};
+
+#if (defined(__STDC_VERSION__) && __STDC_VERSION__ >= 201112l) || \
+  (defined(__cplusplus) && __cplusplus >= 201103L)
+static_assert(sizeof(ZixBTreeNode) == ZIX_BTREE_PAGE_SIZE, "");
+#endif
+
+typedef struct {
+  ZixBTreeNode* node;
+  unsigned      index;
+} ZixBTreeIterFrame;
+
+struct ZixBTreeIterImpl {
+  unsigned          n_levels; ///< Maximum depth of stack
+  unsigned          level;    ///< Current level in stack
+  ZixBTreeIterFrame stack[];  ///< Position stack
+};
+
+#ifdef ZIX_BTREE_DEBUG
+
+static void
+print_node(const ZixBTreeNode* n, const char* prefix)
+{
+  printf("%s[", prefix);
+  for (uint16_t v = 0; v < n->n_vals; ++v) {
+    printf(" %lu", (uintptr_t)n->vals[v]);
+  }
+  printf(" ]\n");
+}
+
+static void
+print_tree(const ZixBTreeNode* parent, const ZixBTreeNode* node, int level)
+{
+  if (node) {
+    if (!parent) {
+      printf("TREE {\n");
+    }
+    for (int i = 0; i < level + 1; ++i) {
+      printf("  ");
+    }
+    print_node(node, "");
+    if (!node->is_leaf) {
+      for (uint16_t i = 0; i < node->n_vals + 1; ++i) {
+        print_tree(node, node->data.inode.children[i], level + 1);
+      }
+    }
+    if (!parent) {
+      printf("}\n");
+    }
+  }
+}
+
+#endif // ZIX_BTREE_DEBUG
+
+static ZixBTreeNode*
+zix_btree_node_new(const bool leaf)
+{
+#if !((defined(__STDC_VERSION__) && __STDC_VERSION__ >= 201112l) || \
+      (defined(__cplusplus) && __cplusplus >= 201103L))
+  assert(sizeof(ZixBTreeNode) == ZIX_BTREE_PAGE_SIZE);
+#endif
+
+  ZixBTreeNode* node = (ZixBTreeNode*)malloc(sizeof(ZixBTreeNode));
+  if (node) {
+    node->is_leaf = leaf;
+    node->n_vals  = 0;
+  }
+  return node;
+}
+
+static void*
+zix_btree_value(const ZixBTreeNode* const node, const unsigned i)
+{
+  assert(i < node->n_vals);
+  return node->is_leaf ? node->data.leaf.vals[i] : node->data.inode.vals[i];
+}
+
+static ZixBTreeNode*
+zix_btree_child(const ZixBTreeNode* const node, const unsigned i)
+{
+  assert(!node->is_leaf);
+  assert(i <= ZIX_BTREE_INODE_VALS);
+  return node->data.inode.children[i];
+}
+
+ZixBTree*
+zix_btree_new(const ZixComparator  cmp,
+              const void* const    cmp_data,
+              const ZixDestroyFunc destroy)
+{
+  ZixBTree* t = (ZixBTree*)malloc(sizeof(ZixBTree));
+  if (t) {
+    t->root     = zix_btree_node_new(true);
+    t->destroy  = destroy;
+    t->cmp      = cmp;
+    t->cmp_data = cmp_data;
+    t->size     = 0;
+    t->height   = 1;
+    if (!t->root) {
+      free(t);
+      return NULL;
+    }
+  }
+  return t;
+}
+
+static void
+zix_btree_free_rec(ZixBTree* const t, ZixBTreeNode* const n)
+{
+  if (n) {
+    if (n->is_leaf) {
+      if (t->destroy) {
+        for (uint16_t i = 0; i < n->n_vals; ++i) {
+          t->destroy(n->data.leaf.vals[i]);
+        }
+      }
+    } else {
+      if (t->destroy) {
+        for (uint16_t i = 0; i < n->n_vals; ++i) {
+          t->destroy(n->data.inode.vals[i]);
+        }
+      }
+
+      for (uint16_t i = 0; i < n->n_vals + 1; ++i) {
+        zix_btree_free_rec(t, zix_btree_child(n, i));
+      }
+    }
+
+    free(n);
+  }
+}
+
+void
+zix_btree_free(ZixBTree* const t)
+{
+  if (t) {
+    zix_btree_free_rec(t, t->root);
+    free(t);
+  }
+}
+
+size_t
+zix_btree_size(const ZixBTree* const t)
+{
+  return t->size;
+}
+
+static uint16_t
+zix_btree_max_vals(const ZixBTreeNode* const node)
+{
+  return node->is_leaf ? ZIX_BTREE_LEAF_VALS : ZIX_BTREE_INODE_VALS;
+}
+
+static uint16_t
+zix_btree_min_vals(const ZixBTreeNode* const node)
+{
+  return (uint16_t)(((zix_btree_max_vals(node) + 1U) / 2U) - 1U);
+}
+
+/** Shift pointers in `array` of length `n` right starting at `i`. */
+static void
+zix_btree_ainsert(void** const   array,
+                  const unsigned n,
+                  const unsigned i,
+                  void* const    e)
+{
+  memmove(array + i + 1, array + i, (n - i) * sizeof(e));
+  array[i] = e;
+}
+
+/** Erase element `i` in `array` of length `n` and return erased element. */
+static void*
+zix_btree_aerase(void** const array, const unsigned n, const unsigned i)
+{
+  void* const ret = array[i];
+  memmove(array + i, array + i + 1, (n - i) * sizeof(ret));
+  return ret;
+}
+
+/** Split lhs, the i'th child of `n`, into two nodes. */
+static ZixBTreeNode*
+zix_btree_split_child(ZixBTreeNode* const n,
+                      const unsigned      i,
+                      ZixBTreeNode* const lhs)
+{
+  assert(lhs->n_vals == zix_btree_max_vals(lhs));
+  assert(n->n_vals < ZIX_BTREE_INODE_VALS);
+  assert(i < n->n_vals + 1U);
+  assert(zix_btree_child(n, i) == lhs);
+
+  const uint16_t max_n_vals = zix_btree_max_vals(lhs);
+  ZixBTreeNode*  rhs        = zix_btree_node_new(lhs->is_leaf);
+  if (!rhs) {
+    return NULL;
+  }
+
+  // LHS and RHS get roughly half, less the middle value which moves up
+  lhs->n_vals = max_n_vals / 2U;
+  rhs->n_vals = (uint16_t)(max_n_vals - lhs->n_vals - 1);
+
+  if (lhs->is_leaf) {
+    // Copy large half from LHS to new RHS node
+    memcpy(rhs->data.leaf.vals,
+           lhs->data.leaf.vals + lhs->n_vals + 1,
+           rhs->n_vals * sizeof(void*));
+
+    // Move middle value up to parent
+    zix_btree_ainsert(
+      n->data.inode.vals, n->n_vals, i, lhs->data.leaf.vals[lhs->n_vals]);
+  } else {
+    // Copy large half from LHS to new RHS node
+    memcpy(rhs->data.inode.vals,
+           lhs->data.inode.vals + lhs->n_vals + 1,
+           rhs->n_vals * sizeof(void*));
+    memcpy(rhs->data.inode.children,
+           lhs->data.inode.children + lhs->n_vals + 1,
+           (rhs->n_vals + 1U) * sizeof(ZixBTreeNode*));
+
+    // Move middle value up to parent
+    zix_btree_ainsert(
+      n->data.inode.vals, n->n_vals, i, lhs->data.inode.vals[lhs->n_vals]);
+  }
+
+  // Insert new RHS node in parent at position i
+  zix_btree_ainsert((void**)n->data.inode.children, ++n->n_vals, i + 1U, rhs);
+
+  return rhs;
+}
+
+#ifdef ZIX_BTREE_SORTED_CHECK
+/** Check that `n` is sorted with respect to search key `e`. */
+static bool
+zix_btree_node_is_sorted_with_respect_to(const ZixBTree* const     t,
+                                         const ZixBTreeNode* const n,
+                                         const void* const         e)
+{
+  if (n->n_vals <= 1) {
+    return true;
+  }
+
+  int cmp = t->cmp(zix_btree_value(n, 0), e, t->cmp_data);
+  for (uint16_t i = 1; i < n->n_vals; ++i) {
+    const int next_cmp = t->cmp(zix_btree_value(n, i), e, t->cmp_data);
+    if ((cmp >= 0 && next_cmp < 0) || (cmp > 0 && next_cmp <= 0)) {
+      return false;
+    }
+    cmp = next_cmp;
+  }
+
+  return true;
+}
+#endif
+
+/** Find the first value in `n` that is not less than `e` (lower bound). */
+static unsigned
+zix_btree_node_find(const ZixBTree* const     t,
+                    const ZixBTreeNode* const n,
+                    const void* const         e,
+                    bool* const               equal)
+{
+#ifdef ZIX_BTREE_SORTED_CHECK
+  assert(zix_btree_node_is_sorted_with_respect_to(t, n, e));
+#endif
+
+  unsigned first = 0U;
+  unsigned len   = n->n_vals;
+  while (len > 0) {
+    const unsigned half = len >> 1U;
+    const unsigned i    = first + half;
+    const int      cmp  = t->cmp(zix_btree_value(n, i), e, t->cmp_data);
+    if (cmp == 0) {
+      *equal = true;
+      len    = half; // Keep searching for wildcard matches
+    } else if (cmp < 0) {
+      const unsigned chop = half + 1U;
+      first += chop;
+      len -= chop;
+    } else {
+      len = half;
+    }
+  }
+
+  assert(!*equal || t->cmp(zix_btree_value(n, first), e, t->cmp_data) == 0);
+  return first;
+}
+
+ZixStatus
+zix_btree_insert(ZixBTree* const t, void* const e)
+{
+  ZixBTreeNode* parent = NULL;    // Parent of n
+  ZixBTreeNode* n      = t->root; // Current node
+  unsigned      i      = 0;       // Index of n in parent
+  while (n) {
+    if (n->n_vals == zix_btree_max_vals(n)) {
+      // Node is full, split to ensure there is space for a leaf split
+      if (!parent) {
+        // Root is full, grow tree upwards
+        if (!(parent = zix_btree_node_new(false))) {
+          return ZIX_STATUS_NO_MEM;
+        }
+        t->root                        = parent;
+        parent->data.inode.children[0] = n;
+        ++t->height;
+      }
+
+      ZixBTreeNode* const rhs = zix_btree_split_child(parent, i, n);
+      if (!rhs) {
+        return ZIX_STATUS_NO_MEM;
+      }
+
+      const int cmp = t->cmp(parent->data.inode.vals[i], e, t->cmp_data);
+      if (cmp == 0) {
+        return ZIX_STATUS_EXISTS;
+      }
+
+      if (cmp < 0) {
+        // Move to new RHS
+        n = rhs;
+        ++i;
+      }
+    }
+
+    assert(!parent || zix_btree_child(parent, i) == n);
+
+    bool equal = false;
+    i          = zix_btree_node_find(t, n, e, &equal);
+    if (equal) {
+      return ZIX_STATUS_EXISTS;
+    }
+
+    if (!n->is_leaf) {
+      // Descend to child node left of value
+      parent = n;
+      n      = zix_btree_child(n, i);
+    } else {
+      // Insert into internal node
+      zix_btree_ainsert(n->data.leaf.vals, n->n_vals++, i, e);
+      break;
+    }
+  }
+
+  ++t->size;
+
+  return ZIX_STATUS_SUCCESS;
+}
+
+static ZixBTreeIter*
+zix_btree_iter_new(const ZixBTree* const t)
+{
+  const size_t s = t->height * sizeof(ZixBTreeIterFrame);
+
+  ZixBTreeIter* i = (ZixBTreeIter*)calloc(1, sizeof(ZixBTreeIter) + s);
+  if (i) {
+    i->n_levels = t->height;
+  }
+  return i;
+}
+
+static void
+zix_btree_iter_set_frame(ZixBTreeIter* const ti,
+                         ZixBTreeNode* const n,
+                         const unsigned      i)
+{
+  if (ti) {
+    ti->stack[ti->level].node  = n;
+    ti->stack[ti->level].index = i;
+  }
+}
+
+static bool
+zix_btree_node_is_minimal(ZixBTreeNode* const n)
+{
+  assert(n->n_vals >= zix_btree_min_vals(n));
+  return n->n_vals == zix_btree_min_vals(n);
+}
+
+/** Enlarge left child by stealing a value from its right sibling. */
+static ZixBTreeNode*
+zix_btree_rotate_left(ZixBTreeNode* const parent, const unsigned i)
+{
+  ZixBTreeNode* const lhs = zix_btree_child(parent, i);
+  ZixBTreeNode* const rhs = zix_btree_child(parent, i + 1);
+
+  assert(lhs->is_leaf == rhs->is_leaf);
+
+  if (lhs->is_leaf) {
+    // Move parent value to end of LHS
+    lhs->data.leaf.vals[lhs->n_vals++] = parent->data.inode.vals[i];
+
+    // Move first value in RHS to parent
+    parent->data.inode.vals[i] =
+      zix_btree_aerase(rhs->data.leaf.vals, rhs->n_vals, 0);
+  } else {
+    // Move parent value to end of LHS
+    lhs->data.inode.vals[lhs->n_vals++] = parent->data.inode.vals[i];
+
+    // Move first value in RHS to parent
+    parent->data.inode.vals[i] =
+      zix_btree_aerase(rhs->data.inode.vals, rhs->n_vals, 0);
+
+    // Move first child pointer from RHS to end of LHS
+    lhs->data.inode.children[lhs->n_vals] = (ZixBTreeNode*)zix_btree_aerase(
+      (void**)rhs->data.inode.children, rhs->n_vals, 0);
+  }
+
+  --rhs->n_vals;
+
+  return lhs;
+}
+
+/** Enlarge right child by stealing a value from its left sibling. */
+static ZixBTreeNode*
+zix_btree_rotate_right(ZixBTreeNode* const parent, const unsigned i)
+{
+  ZixBTreeNode* const lhs = zix_btree_child(parent, i - 1);
+  ZixBTreeNode* const rhs = zix_btree_child(parent, i);
+
+  assert(lhs->is_leaf == rhs->is_leaf);
+
+  if (lhs->is_leaf) {
+    // Prepend parent value to RHS
+    zix_btree_ainsert(
+      rhs->data.leaf.vals, rhs->n_vals++, 0, parent->data.inode.vals[i - 1]);
+
+    // Move last value from LHS to parent
+    parent->data.inode.vals[i - 1] = lhs->data.leaf.vals[--lhs->n_vals];
+  } else {
+    // Prepend parent value to RHS
+    zix_btree_ainsert(
+      rhs->data.inode.vals, rhs->n_vals++, 0, parent->data.inode.vals[i - 1]);
+
+    // Move last child pointer from LHS and prepend to RHS
+    zix_btree_ainsert((void**)rhs->data.inode.children,
+                      rhs->n_vals,
+                      0,
+                      lhs->data.inode.children[lhs->n_vals]);
+
+    // Move last value from LHS to parent
+    parent->data.inode.vals[i - 1] = lhs->data.inode.vals[--lhs->n_vals];
+  }
+
+  return rhs;
+}
+
+/** Move n[i] down, merge the left and right child, return the merged node. */
+static ZixBTreeNode*
+zix_btree_merge(ZixBTree* const t, ZixBTreeNode* const n, const unsigned i)
+{
+  ZixBTreeNode* const lhs = zix_btree_child(n, i);
+  ZixBTreeNode* const rhs = zix_btree_child(n, i + 1);
+
+  assert(lhs->is_leaf == rhs->is_leaf);
+  assert(zix_btree_node_is_minimal(lhs));
+  assert(lhs->n_vals + rhs->n_vals < zix_btree_max_vals(lhs));
+
+  // Move parent value to end of LHS
+  if (lhs->is_leaf) {
+    lhs->data.leaf.vals[lhs->n_vals++] =
+      zix_btree_aerase(n->data.inode.vals, n->n_vals, i);
+  } else {
+    lhs->data.inode.vals[lhs->n_vals++] =
+      zix_btree_aerase(n->data.inode.vals, n->n_vals, i);
+  }
+
+  // Erase corresponding child pointer (to RHS) in parent
+  zix_btree_aerase((void**)n->data.inode.children, n->n_vals, i + 1U);
+
+  // Add everything from RHS to end of LHS
+  if (lhs->is_leaf) {
+    memcpy(lhs->data.leaf.vals + lhs->n_vals,
+           rhs->data.leaf.vals,
+           rhs->n_vals * sizeof(void*));
+  } else {
+    memcpy(lhs->data.inode.vals + lhs->n_vals,
+           rhs->data.inode.vals,
+           rhs->n_vals * sizeof(void*));
+    memcpy(lhs->data.inode.children + lhs->n_vals,
+           rhs->data.inode.children,
+           (rhs->n_vals + 1U) * sizeof(void*));
+  }
+
+  lhs->n_vals = (uint16_t)(lhs->n_vals + rhs->n_vals);
+
+  if (--n->n_vals == 0) {
+    // Root is now empty, replace it with its only child
+    assert(n == t->root);
+    t->root = lhs;
+    free(n);
+  }
+
+  free(rhs);
+  return lhs;
+}
+
+/** Remove and return the min value from the subtree rooted at `n`. */
+static void*
+zix_btree_remove_min(ZixBTree* const t, ZixBTreeNode* n)
+{
+  while (!n->is_leaf) {
+    if (zix_btree_node_is_minimal(zix_btree_child(n, 0))) {
+      // Leftmost child is minimal, must expand
+      if (!zix_btree_node_is_minimal(zix_btree_child(n, 1))) {
+        // Child's right sibling has at least one key to steal
+        n = zix_btree_rotate_left(n, 0);
+      } else {
+        // Both child and right sibling are minimal, merge
+        n = zix_btree_merge(t, n, 0);
+      }
+    } else {
+      n = zix_btree_child(n, 0);
+    }
+  }
+
+  return zix_btree_aerase(n->data.leaf.vals, --n->n_vals, 0);
+}
+
+/** Remove and return the max value from the subtree rooted at `n`. */
+static void*
+zix_btree_remove_max(ZixBTree* const t, ZixBTreeNode* n)
+{
+  while (!n->is_leaf) {
+    if (zix_btree_node_is_minimal(zix_btree_child(n, n->n_vals))) {
+      // Leftmost child is minimal, must expand
+      if (!zix_btree_node_is_minimal(zix_btree_child(n, n->n_vals - 1u))) {
+        // Child's left sibling has at least one key to steal
+        n = zix_btree_rotate_right(n, n->n_vals);
+      } else {
+        // Both child and left sibling are minimal, merge
+        n = zix_btree_merge(t, n, n->n_vals - 1U);
+      }
+    } else {
+      n = zix_btree_child(n, n->n_vals);
+    }
+  }
+
+  return n->data.leaf.vals[--n->n_vals];
+}
+
+ZixStatus
+zix_btree_remove(ZixBTree* const      t,
+                 const void* const    e,
+                 void** const         out,
+                 ZixBTreeIter** const next)
+{
+  ZixBTreeNode* n         = t->root;
+  ZixBTreeIter* ti        = NULL;
+  const bool    user_iter = next && *next;
+  if (next) {
+    if (!*next && !(*next = zix_btree_iter_new(t))) {
+      return ZIX_STATUS_NO_MEM;
+    }
+    ti        = *next;
+    ti->level = 0;
+  }
+
+  while (true) {
+    /* To remove in a single walk down, the tree is adjusted along the way
+       so that the current node always has at least one more value than the
+       minimum required in general. Thus, there is always room to remove
+       without adjusting on the way back up. */
+    assert(n == t->root || !zix_btree_node_is_minimal(n));
+
+    bool           equal = false;
+    const unsigned i     = zix_btree_node_find(t, n, e, &equal);
+    zix_btree_iter_set_frame(ti, n, i);
+    if (n->is_leaf) {
+      if (equal) {
+        // Found in leaf node
+        *out = zix_btree_aerase(n->data.leaf.vals, --n->n_vals, i);
+        if (ti && i == n->n_vals) {
+          if (i == 0) {
+            ti->level         = 0;
+            ti->stack[0].node = NULL;
+          } else {
+            --ti->stack[ti->level].index;
+            zix_btree_iter_increment(ti);
+          }
+        }
+        --t->size;
+        return ZIX_STATUS_SUCCESS;
+      }
+
+      // Not found in leaf node, or tree
+      if (ti && !user_iter) {
+        zix_btree_iter_free(ti);
+        *next = NULL;
+      }
+
+      return ZIX_STATUS_NOT_FOUND;
+    }
+
+    if (equal) {
+      // Found in internal node
+      ZixBTreeNode* const lhs    = zix_btree_child(n, i);
+      ZixBTreeNode* const rhs    = zix_btree_child(n, i + 1);
+      const size_t        l_size = lhs->n_vals;
+      const size_t        r_size = rhs->n_vals;
+      if (zix_btree_node_is_minimal(lhs) && zix_btree_node_is_minimal(rhs)) {
+        // Both preceding and succeeding child are minimal
+        n = zix_btree_merge(t, n, i);
+      } else if (l_size >= r_size) {
+        // Left child can remove without merge
+        assert(!zix_btree_node_is_minimal(lhs));
+        *out                  = n->data.inode.vals[i];
+        n->data.inode.vals[i] = zix_btree_remove_max(t, lhs);
+        --t->size;
+        return ZIX_STATUS_SUCCESS;
+      } else {
+        // Right child can remove without merge
+        assert(!zix_btree_node_is_minimal(rhs));
+        *out                  = n->data.inode.vals[i];
+        n->data.inode.vals[i] = zix_btree_remove_min(t, rhs);
+        --t->size;
+        return ZIX_STATUS_SUCCESS;
+      }
+    } else {
+      // Not found in internal node, key is in/under children[i]
+      if (zix_btree_node_is_minimal(zix_btree_child(n, i))) {
+        if (i > 0 && !zix_btree_node_is_minimal(zix_btree_child(n, i - 1))) {
+          // Steal a key from child's left sibling
+          n = zix_btree_rotate_right(n, i);
+        } else if (i < n->n_vals &&
+                   !zix_btree_node_is_minimal(zix_btree_child(n, i + 1))) {
+          // Steal a key from child's right sibling
+          n = zix_btree_rotate_left(n, i);
+        } else if (n == t->root && n->n_vals == 1) {
+          // Root has two children, both minimal, delete it
+          assert(i == 0 || i == 1);
+          const uint16_t counts[2] = {zix_btree_child(n, 0)->n_vals,
+                                      zix_btree_child(n, 1)->n_vals};
+
+          n = zix_btree_merge(t, n, 0);
+          if (ti) {
+            ti->stack[ti->level].node  = n;
+            ti->stack[ti->level].index = counts[i];
+          }
+        } else {
+          // Both child's siblings are minimal, merge them
+          if (i < n->n_vals) {
+            n = zix_btree_merge(t, n, i);
+          } else {
+            n = zix_btree_merge(t, n, i - 1U);
+            if (ti) {
+              --ti->stack[ti->level].index;
+            }
+          }
+        }
+      } else {
+        n = zix_btree_child(n, i);
+      }
+    }
+    if (ti) {
+      ++ti->level;
+    }
+  }
+
+  assert(false); // Not reached
+  return ZIX_STATUS_ERROR;
+}
+
+ZixStatus
+zix_btree_find(const ZixBTree* const t,
+               const void* const     e,
+               ZixBTreeIter** const  ti)
+{
+  ZixBTreeNode* n = t->root;
+  if (!(*ti = zix_btree_iter_new(t))) {
+    return ZIX_STATUS_NO_MEM;
+  }
+
+  while (n) {
+    bool           equal = false;
+    const unsigned i     = zix_btree_node_find(t, n, e, &equal);
+
+    zix_btree_iter_set_frame(*ti, n, i);
+
+    if (equal) {
+      return ZIX_STATUS_SUCCESS;
+    }
+
+    if (n->is_leaf) {
+      break;
+    }
+
+    ++(*ti)->level;
+    n = zix_btree_child(n, i);
+  }
+
+  zix_btree_iter_free(*ti);
+  *ti = NULL;
+  return ZIX_STATUS_NOT_FOUND;
+}
+
+ZixStatus
+zix_btree_lower_bound(const ZixBTree* const t,
+                      const void* const     e,
+                      ZixBTreeIter** const  ti)
+{
+  if (!t) {
+    *ti = NULL;
+    return ZIX_STATUS_BAD_ARG;
+  }
+
+  if (!t->root) {
+    *ti = NULL;
+    return ZIX_STATUS_SUCCESS;
+  }
+
+  ZixBTreeNode* n           = t->root;
+  bool          found       = false;
+  unsigned      found_level = 0;
+  if (!(*ti = zix_btree_iter_new(t))) {
+    return ZIX_STATUS_NO_MEM;
+  }
+
+  while (n) {
+    bool           equal = false;
+    const unsigned i     = zix_btree_node_find(t, n, e, &equal);
+
+    zix_btree_iter_set_frame(*ti, n, i);
+
+    if (equal) {
+      found_level = (*ti)->level;
+      found       = true;
+    }
+
+    if (n->is_leaf) {
+      break;
+    }
+
+    ++(*ti)->level;
+    n = zix_btree_child(n, i);
+    assert(n);
+  }
+
+  const ZixBTreeIterFrame* const frame = &(*ti)->stack[(*ti)->level];
+  assert(frame->node);
+  if (frame->index == frame->node->n_vals) {
+    if (found) {
+      // Found on a previous level but went too far
+      (*ti)->level = found_level;
+    } else {
+      // Reached end (key is greater than everything in tree)
+      (*ti)->level         = 0;
+      (*ti)->stack[0].node = NULL;
+    }
+  }
+
+  return ZIX_STATUS_SUCCESS;
+}
+
+void*
+zix_btree_get(const ZixBTreeIter* const ti)
+{
+  const ZixBTreeIterFrame* const frame = &ti->stack[ti->level];
+  assert(frame->node);
+  assert(frame->index < frame->node->n_vals);
+  return zix_btree_value(frame->node, frame->index);
+}
+
+ZixBTreeIter*
+zix_btree_begin(const ZixBTree* const t)
+{
+  ZixBTreeIter* const i = zix_btree_iter_new(t);
+  if (!i) {
+    return NULL;
+  }
+
+  if (t->size == 0) {
+    i->level         = 0;
+    i->stack[0].node = NULL;
+  } else {
+    ZixBTreeNode* n   = t->root;
+    i->stack[0].node  = n;
+    i->stack[0].index = 0;
+    while (!n->is_leaf) {
+      n = zix_btree_child(n, 0);
+      ++i->level;
+      i->stack[i->level].node  = n;
+      i->stack[i->level].index = 0;
+    }
+  }
+
+  return i;
+}
+
+ZixBTreeIter*
+zix_btree_end(const ZixBTree* const t)
+{
+  return zix_btree_iter_new(t);
+}
+
+ZixBTreeIter*
+zix_btree_iter_copy(const ZixBTreeIter* const i)
+{
+  if (!i) {
+    return NULL;
+  }
+
+  const size_t  s = i->n_levels * sizeof(ZixBTreeIterFrame);
+  ZixBTreeIter* j = (ZixBTreeIter*)calloc(1, sizeof(ZixBTreeIter) + s);
+  if (j) {
+    memcpy(j, i, sizeof(ZixBTreeIter) + s);
+  }
+
+  return j;
+}
+
+bool
+zix_btree_iter_is_end(const ZixBTreeIter* const i)
+{
+  return !i || (i->level == 0 && i->stack[0].node == NULL);
+}
+
+bool
+zix_btree_iter_equals(const ZixBTreeIter* const lhs,
+                      const ZixBTreeIter* const rhs)
+{
+  if (zix_btree_iter_is_end(lhs) && zix_btree_iter_is_end(rhs)) {
+    return true;
+  }
+
+  if (zix_btree_iter_is_end(lhs) || zix_btree_iter_is_end(rhs) ||
+      lhs->level != rhs->level) {
+    return false;
+  }
+
+  return !memcmp(lhs,
+                 rhs,
+                 sizeof(ZixBTreeIter) +
+                   (lhs->level + 1) * sizeof(ZixBTreeIterFrame));
+}
+
+void
+zix_btree_iter_increment(ZixBTreeIter* const i)
+{
+  ZixBTreeIterFrame* f = &i->stack[i->level];
+  if (f->node->is_leaf) {
+    // Leaf, move right
+    assert(f->index < f->node->n_vals);
+    if (++f->index == f->node->n_vals) {
+      // Reached end of leaf, move up
+      f = &i->stack[i->level];
+      while (i->level > 0 && f->index == f->node->n_vals) {
+        f = &i->stack[--i->level];
+        assert(f->index <= f->node->n_vals);
+      }
+
+      if (f->index == f->node->n_vals) {
+        // Reached end of tree
+        assert(i->level == 0);
+        f->node  = NULL;
+        f->index = 0;
+      }
+    }
+  } else {
+    // Internal node, move down to next child
+    assert(f->index < f->node->n_vals);
+    ZixBTreeNode* child = zix_btree_child(f->node, ++f->index);
+
+    f        = &i->stack[++i->level];
+    f->node  = child;
+    f->index = 0;
+
+    // Move down and left until we hit a leaf
+    while (!f->node->is_leaf) {
+      child    = zix_btree_child(f->node, 0);
+      f        = &i->stack[++i->level];
+      f->node  = child;
+      f->index = 0;
+    }
+  }
+}
+
+void
+zix_btree_iter_free(ZixBTreeIter* const i)
+{
+  free(i);
+}
diff --git a/src/zix/btree.h b/src/zix/btree.h
new file mode 100644
index 00000000..bec06988
--- /dev/null
+++ b/src/zix/btree.h
@@ -0,0 +1,187 @@
+/*
+  Copyright 2011-2020 David Robillard <d@drobilla.net>
+
+  Permission to use, copy, modify, and/or distribute this software for any
+  purpose with or without fee is hereby granted, provided that the above
+  copyright notice and this permission notice appear in all copies.
+
+  THIS 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.
+*/
+
+#ifndef ZIX_BTREE_H
+#define ZIX_BTREE_H
+
+#include "zix/common.h"
+
+#include <stdbool.h>
+#include <stddef.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+   @addtogroup zix
+   @{
+   @name BTree
+   @{
+*/
+
+/**
+   A B-Tree.
+*/
+typedef struct ZixBTreeImpl ZixBTree;
+
+/**
+   A B-Tree node (opaque).
+*/
+typedef struct ZixBTreeNodeImpl ZixBTreeNode;
+
+/**
+   An iterator over a B-Tree.
+
+   Note that modifying the trees invalidates all iterators, so all iterators
+   are const iterators.
+*/
+typedef struct ZixBTreeIterImpl ZixBTreeIter;
+
+/**
+   Create a new (empty) B-Tree.
+*/
+ZIX_API
+ZixBTree*
+zix_btree_new(ZixComparator cmp, const void* cmp_data, ZixDestroyFunc destroy);
+
+/**
+   Free `t`.
+*/
+ZIX_API
+void
+zix_btree_free(ZixBTree* t);
+
+/**
+   Return the number of elements in `t`.
+*/
+ZIX_PURE_API
+size_t
+zix_btree_size(const ZixBTree* t);
+
+/**
+   Insert the element `e` into `t`.
+*/
+ZIX_API
+ZixStatus
+zix_btree_insert(ZixBTree* t, void* e);
+
+/**
+   Remove the value `e` from `t`.
+
+   @param t Tree to remove from.
+
+   @param e Value to remove.
+
+   @param out Set to point to the removed pointer (which may not equal `e`).
+
+   @param next If non-NULL, pointed to the value following `e`.  If *next is
+   also non-NULL, the iterator is reused, otherwise a new one is allocated.  To
+   reuse an iterator, no items may have been added since its creation.
+*/
+ZIX_API
+ZixStatus
+zix_btree_remove(ZixBTree* t, const void* e, void** out, ZixBTreeIter** next);
+
+/**
+   Set `ti` to an element equal to `e` in `t`.
+   If no such item exists, `ti` is set to NULL.
+*/
+ZIX_API
+ZixStatus
+zix_btree_find(const ZixBTree* t, const void* e, ZixBTreeIter** ti);
+
+/**
+   Set `ti` to the smallest element in `t` that is not less than `e`.
+
+   Wildcards are supported, so if the search key `e` compares equal to many
+   values in the tree, `ti` will be set to the least such element.  The search
+   key `e` is always passed as the second argument to the comparator.
+*/
+ZIX_API
+ZixStatus
+zix_btree_lower_bound(const ZixBTree* t, const void* e, ZixBTreeIter** ti);
+
+/**
+   Return the data associated with the given tree item.
+*/
+ZIX_PURE_API
+void*
+zix_btree_get(const ZixBTreeIter* ti);
+
+/**
+   Return an iterator to the first (smallest) element in `t`.
+
+   The returned iterator must be freed with zix_btree_iter_free().
+*/
+ZIX_PURE_API
+ZixBTreeIter*
+zix_btree_begin(const ZixBTree* t);
+
+/**
+   Return an iterator to the end of `t` (one past the last element).
+
+   The returned iterator must be freed with zix_btree_iter_free().
+*/
+ZIX_API
+ZixBTreeIter*
+zix_btree_end(const ZixBTree* t);
+
+/**
+   Return a new copy of `i`.
+*/
+ZIX_API
+ZixBTreeIter*
+zix_btree_iter_copy(const ZixBTreeIter* i);
+
+/**
+   Return true iff `lhs` is equal to `rhs`.
+*/
+ZIX_PURE_API
+bool
+zix_btree_iter_equals(const ZixBTreeIter* lhs, const ZixBTreeIter* rhs);
+
+/**
+   Return true iff `i` is an iterator to the end of its tree.
+*/
+ZIX_PURE_API
+bool
+zix_btree_iter_is_end(const ZixBTreeIter* i);
+
+/**
+   Increment `i` to point to the next element in the tree.
+*/
+ZIX_API
+void
+zix_btree_iter_increment(ZixBTreeIter* i);
+
+/**
+   Free `i`.
+*/
+ZIX_API
+void
+zix_btree_iter_free(ZixBTreeIter* i);
+
+/**
+   @}
+   @}
+*/
+
+#ifdef __cplusplus
+} /* extern "C" */
+#endif
+
+#endif /* ZIX_BTREE_H */
diff --git a/src/zix/common.h b/src/zix/common.h
new file mode 100644
index 00000000..d47586c6
--- /dev/null
+++ b/src/zix/common.h
@@ -0,0 +1,138 @@
+/*
+  Copyright 2016-2020 David Robillard <d@drobilla.net>
+
+  Permission to use, copy, modify, and/or distribute this software for any
+  purpose with or without fee is hereby granted, provided that the above
+  copyright notice and this permission notice appear in all copies.
+
+  THIS 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.
+*/
+
+#ifndef ZIX_COMMON_H
+#define ZIX_COMMON_H
+
+#include <stdbool.h>
+
+/**
+   @addtogroup zix
+   @{
+*/
+
+/** @cond */
+#if defined(_WIN32) && !defined(ZIX_STATIC) && defined(ZIX_INTERNAL)
+#  define ZIX_API __declspec(dllexport)
+#elif defined(_WIN32) && !defined(ZIX_STATIC)
+#  define ZIX_API __declspec(dllimport)
+#elif defined(__GNUC__)
+#  define ZIX_API __attribute__((visibility("default")))
+#else
+#  define ZIX_API
+#endif
+
+#ifdef __GNUC__
+#  define ZIX_PURE_FUNC __attribute__((pure))
+#  define ZIX_CONST_FUNC __attribute__((const))
+#  define ZIX_MALLOC_FUNC __attribute__((malloc))
+#else
+#  define ZIX_PURE_FUNC
+#  define ZIX_CONST_FUNC
+#  define ZIX_MALLOC_FUNC
+#endif
+
+#define ZIX_PURE_API \
+  ZIX_API            \
+  ZIX_PURE_FUNC
+
+#define ZIX_CONST_API \
+  ZIX_API             \
+  ZIX_CONST_FUNC
+
+#define ZIX_MALLOC_API \
+  ZIX_API              \
+  ZIX_MALLOC_FUNC
+
+/** @endcond */
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#ifdef __GNUC__
+#  define ZIX_LOG_FUNC(fmt, arg1) __attribute__((format(printf, fmt, arg1)))
+#else
+#  define ZIX_LOG_FUNC(fmt, arg1)
+#endif
+
+// Unused parameter macro to suppresses warnings and make it impossible to use
+#if defined(__cplusplus)
+#  define ZIX_UNUSED(name)
+#elif defined(__GNUC__)
+#  define ZIX_UNUSED(name) name##_unused __attribute__((__unused__))
+#else
+#  define ZIX_UNUSED(name) name
+#endif
+
+typedef enum {
+  ZIX_STATUS_SUCCESS,
+  ZIX_STATUS_ERROR,
+  ZIX_STATUS_NO_MEM,
+  ZIX_STATUS_NOT_FOUND,
+  ZIX_STATUS_EXISTS,
+  ZIX_STATUS_BAD_ARG,
+  ZIX_STATUS_BAD_PERMS
+} ZixStatus;
+
+static inline const char*
+zix_strerror(const ZixStatus status)
+{
+  switch (status) {
+  case ZIX_STATUS_SUCCESS:
+    return "Success";
+  case ZIX_STATUS_ERROR:
+    return "Unknown error";
+  case ZIX_STATUS_NO_MEM:
+    return "Out of memory";
+  case ZIX_STATUS_NOT_FOUND:
+    return "Not found";
+  case ZIX_STATUS_EXISTS:
+    return "Exists";
+  case ZIX_STATUS_BAD_ARG:
+    return "Bad argument";
+  case ZIX_STATUS_BAD_PERMS:
+    return "Bad permissions";
+  }
+  return "Unknown error";
+}
+
+/**
+   Function for comparing two elements.
+*/
+typedef int (*ZixComparator)(const void* a,
+                             const void* b,
+                             const void* user_data);
+
+/**
+   Function for testing equality of two elements.
+*/
+typedef bool (*ZixEqualFunc)(const void* a, const void* b);
+
+/**
+   Function to destroy an element.
+*/
+typedef void (*ZixDestroyFunc)(void* ptr);
+
+/**
+   @}
+*/
+
+#ifdef __cplusplus
+} /* extern "C" */
+#endif
+
+#endif /* ZIX_COMMON_H */
diff --git a/src/zix/digest.c b/src/zix/digest.c
new file mode 100644
index 00000000..47d27b94
--- /dev/null
+++ b/src/zix/digest.c
@@ -0,0 +1,141 @@
+/*
+  Copyright 2012-2020 David Robillard <d@drobilla.net>
+
+  Permission to use, copy, modify, and/or distribute this software for any
+  purpose with or without fee is hereby granted, provided that the above
+  copyright notice and this permission notice appear in all copies.
+
+  THIS 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.
+*/
+
+#include "zix/digest.h"
+
+#ifdef __SSE4_2__
+#  include <smmintrin.h>
+#endif
+
+#include <assert.h>
+#include <stdint.h>
+
+#ifdef __SSE4_2__
+
+// SSE 4.2 CRC32
+
+uint32_t
+zix_digest_start(void)
+{
+  return 1;
+}
+
+uint32_t
+zix_digest_add(uint32_t hash, const void* const buf, const size_t len)
+{
+  const uint8_t* str = (const uint8_t*)buf;
+
+#  ifdef __x86_64__
+  for (size_t i = 0; i < (len / sizeof(uint64_t)); ++i) {
+    hash = (uint32_t)_mm_crc32_u64(hash, *(const uint64_t*)str);
+    str += sizeof(uint64_t);
+  }
+  if (len & sizeof(uint32_t)) {
+    hash = _mm_crc32_u32(hash, *(const uint32_t*)str);
+    str += sizeof(uint32_t);
+  }
+#  else
+  for (size_t i = 0; i < (len / sizeof(uint32_t)); ++i) {
+    hash = _mm_crc32_u32(hash, *(const uint32_t*)str);
+    str += sizeof(uint32_t);
+  }
+#  endif
+  if (len & sizeof(uint16_t)) {
+    hash = _mm_crc32_u16(hash, *(const uint16_t*)str);
+    str += sizeof(uint16_t);
+  }
+  if (len & sizeof(uint8_t)) {
+    hash = _mm_crc32_u8(hash, *(const uint8_t*)str);
+  }
+
+  return hash;
+}
+
+uint32_t
+zix_digest_add_64(uint32_t hash, const void* const buf, const size_t len)
+{
+  assert((uintptr_t)buf % sizeof(uint64_t) == 0);
+  assert(len % sizeof(uint64_t) == 0);
+
+#  ifdef __x86_64__
+  const uint64_t* ptr = (const uint64_t*)buf;
+
+  for (size_t i = 0; i < (len / sizeof(uint64_t)); ++i) {
+    hash = (uint32_t)_mm_crc32_u64(hash, *ptr);
+    ++ptr;
+  }
+
+  return hash;
+#  else
+  const uint32_t* ptr = (const uint32_t*)buf;
+
+  for (size_t i = 0; i < (len / sizeof(uint32_t)); ++i) {
+    hash = _mm_crc32_u32(hash, *ptr);
+    ++ptr;
+  }
+
+  return hash;
+#  endif
+}
+
+uint32_t
+zix_digest_add_ptr(const uint32_t hash, const void* const ptr)
+{
+#  ifdef __x86_64__
+  return (uint32_t)_mm_crc32_u64(hash, (uintptr_t)ptr);
+#  else
+  return _mm_crc32_u32(hash, (uintptr_t)ptr);
+#  endif
+}
+
+#else
+
+// Classic DJB hash
+
+uint32_t
+zix_digest_start(void)
+{
+  return 5381;
+}
+
+uint32_t
+zix_digest_add(uint32_t hash, const void* const buf, const size_t len)
+{
+  const uint8_t* str = (const uint8_t*)buf;
+
+  for (size_t i = 0; i < len; ++i) {
+    hash = (hash << 5u) + hash + str[i];
+  }
+
+  return hash;
+}
+
+uint32_t
+zix_digest_add_64(uint32_t hash, const void* const buf, const size_t len)
+{
+  assert((uintptr_t)buf % sizeof(uint64_t) == 0);
+  assert(len % sizeof(uint64_t) == 0);
+
+  return zix_digest_add(hash, buf, len);
+}
+
+uint32_t
+zix_digest_add_ptr(const uint32_t hash, const void* const ptr)
+{
+  return zix_digest_add(hash, &ptr, sizeof(ptr));
+}
+
+#endif
diff --git a/src/zix/digest.h b/src/zix/digest.h
new file mode 100644
index 00000000..1fde77a9
--- /dev/null
+++ b/src/zix/digest.h
@@ -0,0 +1,67 @@
+/*
+  Copyright 2012-2020 David Robillard <d@drobilla.net>
+
+  Permission to use, copy, modify, and/or distribute this software for any
+  purpose with or without fee is hereby granted, provided that the above
+  copyright notice and this permission notice appear in all copies.
+
+  THIS 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.
+*/
+
+#ifndef ZIX_DIGEST_H
+#define ZIX_DIGEST_H
+
+#include "zix/common.h"
+
+#include <stddef.h>
+#include <stdint.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+   Return an initial empty digest value.
+*/
+ZIX_CONST_API
+uint32_t
+zix_digest_start(void);
+
+/**
+   Update `hash` to include `buf`, a buffer of `len` bytes.
+
+   This can be used for any size or alignment.
+*/
+ZIX_PURE_API
+uint32_t
+zix_digest_add(uint32_t hash, const void* buf, size_t len);
+
+/**
+   Update `hash` to include `buf`, a 64-bit aligned buffer of `len` bytes.
+
+   Both `buf` and `len` must be evenly divisible by 8 (64 bits).
+*/
+ZIX_PURE_API
+uint32_t
+zix_digest_add_64(uint32_t hash, const void* buf, size_t len);
+
+/**
+   Update `hash` to include `ptr`.
+
+   This hashes the value of the pointer itself, and does not dereference `ptr`.
+*/
+ZIX_CONST_API
+uint32_t
+zix_digest_add_ptr(uint32_t hash, const void* ptr);
+
+#ifdef __cplusplus
+} /* extern "C" */
+#endif
+
+#endif /* ZIX_DIGEST_H */
diff --git a/src/zix/hash.c b/src/zix/hash.c
new file mode 100644
index 00000000..81830820
--- /dev/null
+++ b/src/zix/hash.c
@@ -0,0 +1,230 @@
+/*
+  Copyright 2011-2020 David Robillard <d@drobilla.net>
+
+  Permission to use, copy, modify, and/or distribute this software for any
+  purpose with or without fee is hereby granted, provided that the above
+  copyright notice and this permission notice appear in all copies.
+
+  THIS 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.
+*/
+
+#include "zix/hash.h"
+
+#include <assert.h>
+#include <stdlib.h>
+#include <string.h>
+
+/**
+   Primes, each slightly less than twice its predecessor, and as far away
+   from powers of two as possible.
+*/
+static const unsigned sizes[] = {
+  53,        97,        193,       389,       769,        1543,     3079,
+  6151,      12289,     24593,     49157,     98317,      196613,   393241,
+  786433,    1572869,   3145739,   6291469,   12582917,   25165843, 50331653,
+  100663319, 201326611, 402653189, 805306457, 1610612741, 0};
+
+typedef struct ZixHashEntry {
+  struct ZixHashEntry* next; ///< Next entry in bucket
+  uint32_t             hash; ///< Non-modulo hash value
+                             // Value follows here (access with zix_hash_value)
+} ZixHashEntry;
+
+struct ZixHashImpl {
+  ZixHashFunc     hash_func;
+  ZixEqualFunc    equal_func;
+  ZixHashEntry**  buckets;
+  const unsigned* n_buckets;
+  size_t          value_size;
+  unsigned        count;
+};
+
+static inline void*
+zix_hash_value(ZixHashEntry* entry)
+{
+  return entry + 1;
+}
+
+ZixHash*
+zix_hash_new(ZixHashFunc hash_func, ZixEqualFunc equal_func, size_t value_size)
+{
+  ZixHash* hash = (ZixHash*)malloc(sizeof(ZixHash));
+  if (hash) {
+    hash->hash_func  = hash_func;
+    hash->equal_func = equal_func;
+    hash->n_buckets  = &sizes[0];
+    hash->value_size = value_size;
+    hash->count      = 0;
+    if (!(hash->buckets =
+            (ZixHashEntry**)calloc(*hash->n_buckets, sizeof(ZixHashEntry*)))) {
+      free(hash);
+      return NULL;
+    }
+  }
+  return hash;
+}
+
+void
+zix_hash_free(ZixHash* hash)
+{
+  if (!hash) {
+    return;
+  }
+
+  for (unsigned b = 0; b < *hash->n_buckets; ++b) {
+    ZixHashEntry* bucket = hash->buckets[b];
+    for (ZixHashEntry* e = bucket; e;) {
+      ZixHashEntry* next = e->next;
+      free(e);
+      e = next;
+    }
+  }
+
+  free(hash->buckets);
+  free(hash);
+}
+
+size_t
+zix_hash_size(const ZixHash* hash)
+{
+  return hash->count;
+}
+
+static inline void
+insert_entry(ZixHashEntry** bucket, ZixHashEntry* entry)
+{
+  entry->next = *bucket;
+  *bucket     = entry;
+}
+
+static inline ZixStatus
+rehash(ZixHash* hash, unsigned new_n_buckets)
+{
+  ZixHashEntry** new_buckets =
+    (ZixHashEntry**)calloc(new_n_buckets, sizeof(ZixHashEntry*));
+  if (!new_buckets) {
+    return ZIX_STATUS_NO_MEM;
+  }
+
+  const unsigned old_n_buckets = *hash->n_buckets;
+  for (unsigned b = 0; b < old_n_buckets; ++b) {
+    for (ZixHashEntry* e = hash->buckets[b]; e;) {
+      ZixHashEntry* const next = e->next;
+      const unsigned      h    = e->hash % new_n_buckets;
+      insert_entry(&new_buckets[h], e);
+      e = next;
+    }
+  }
+
+  free(hash->buckets);
+  hash->buckets = new_buckets;
+
+  return ZIX_STATUS_SUCCESS;
+}
+
+static inline ZixHashEntry*
+find_entry(const ZixHash* hash,
+           const void*    key,
+           const unsigned h,
+           const unsigned h_nomod)
+{
+  for (ZixHashEntry* e = hash->buckets[h]; e; e = e->next) {
+    if (e->hash == h_nomod && hash->equal_func(zix_hash_value(e), key)) {
+      return e;
+    }
+  }
+  return NULL;
+}
+
+void*
+zix_hash_find(const ZixHash* hash, const void* value)
+{
+  const unsigned      h_nomod = hash->hash_func(value);
+  const unsigned      h       = h_nomod % *hash->n_buckets;
+  ZixHashEntry* const entry   = find_entry(hash, value, h, h_nomod);
+  return entry ? zix_hash_value(entry) : 0;
+}
+
+ZixStatus
+zix_hash_insert(ZixHash* hash, const void* value, void** inserted)
+{
+  unsigned h_nomod = hash->hash_func(value);
+  unsigned h       = h_nomod % *hash->n_buckets;
+
+  ZixHashEntry* elem = find_entry(hash, value, h, h_nomod);
+  if (elem) {
+    assert(elem->hash == h_nomod);
+    if (inserted) {
+      *inserted = zix_hash_value(elem);
+    }
+    return ZIX_STATUS_EXISTS;
+  }
+
+  elem = (ZixHashEntry*)malloc(sizeof(ZixHashEntry) + hash->value_size);
+  if (!elem) {
+    return ZIX_STATUS_NO_MEM;
+  }
+  elem->next = NULL;
+  elem->hash = h_nomod;
+  memcpy(elem + 1, value, hash->value_size);
+
+  const unsigned next_n_buckets = *(hash->n_buckets + 1);
+  if (next_n_buckets != 0 && (hash->count + 1) >= next_n_buckets) {
+    if (!rehash(hash, next_n_buckets)) {
+      h = h_nomod % *(++hash->n_buckets);
+    }
+  }
+
+  insert_entry(&hash->buckets[h], elem);
+  ++hash->count;
+  if (inserted) {
+    *inserted = zix_hash_value(elem);
+  }
+  return ZIX_STATUS_SUCCESS;
+}
+
+ZixStatus
+zix_hash_remove(ZixHash* hash, const void* value)
+{
+  const unsigned h_nomod = hash->hash_func(value);
+  const unsigned h       = h_nomod % *hash->n_buckets;
+
+  ZixHashEntry** next_ptr = &hash->buckets[h];
+  for (ZixHashEntry* e = hash->buckets[h]; e; e = e->next) {
+    if (h_nomod == e->hash && hash->equal_func(zix_hash_value(e), value)) {
+      *next_ptr = e->next;
+      free(e);
+      return ZIX_STATUS_SUCCESS;
+    }
+    next_ptr = &e->next;
+  }
+
+  if (hash->n_buckets != sizes) {
+    const unsigned prev_n_buckets = *(hash->n_buckets - 1);
+    if (hash->count - 1 <= prev_n_buckets) {
+      if (!rehash(hash, prev_n_buckets)) {
+        --hash->n_buckets;
+      }
+    }
+  }
+
+  --hash->count;
+  return ZIX_STATUS_NOT_FOUND;
+}
+
+void
+zix_hash_foreach(ZixHash* hash, ZixHashVisitFunc f, void* user_data)
+{
+  for (unsigned b = 0; b < *hash->n_buckets; ++b) {
+    ZixHashEntry* bucket = hash->buckets[b];
+    for (ZixHashEntry* e = bucket; e; e = e->next) {
+      f(zix_hash_value(e), user_data);
+    }
+  }
+}
diff --git a/src/zix/hash.h b/src/zix/hash.h
new file mode 100644
index 00000000..39050381
--- /dev/null
+++ b/src/zix/hash.h
@@ -0,0 +1,138 @@
+/*
+  Copyright 2011-2020 David Robillard <d@drobilla.net>
+
+  Permission to use, copy, modify, and/or distribute this software for any
+  purpose with or without fee is hereby granted, provided that the above
+  copyright notice and this permission notice appear in all copies.
+
+  THIS 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.
+*/
+
+#ifndef ZIX_HASH_H
+#define ZIX_HASH_H
+
+#include "zix/common.h"
+
+#include <stddef.h>
+#include <stdint.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+   @addtogroup zix
+   @{
+   @name Hash
+   @{
+*/
+
+typedef struct ZixHashImpl ZixHash;
+
+/**
+   Function for computing the hash of an element.
+*/
+typedef uint32_t (*ZixHashFunc)(const void* value);
+
+/**
+   Function to visit a hash element.
+*/
+typedef void (*ZixHashVisitFunc)(void* value, void* user_data);
+
+/**
+   Create a new hash table.
+
+   To minimize space overhead, unlike many hash tables this stores a single
+   value, not a key and a value.  Any size of value can be stored, but all the
+   values in the hash table must be the same size, and the values must be safe
+   to copy with memcpy.  To get key:value behaviour, simply insert a struct
+   with a key and value into the hash.
+
+   @param hash_func The hashing function.
+   @param equal_func A function to test value equality.
+   @param value_size The size of the values to be stored.
+*/
+ZIX_API
+ZixHash*
+zix_hash_new(ZixHashFunc hash_func, ZixEqualFunc equal_func, size_t value_size);
+
+/**
+   Free `hash`.
+*/
+ZIX_API
+void
+zix_hash_free(ZixHash* hash);
+
+/**
+   Return the number of elements in `hash`.
+*/
+ZIX_PURE_API
+size_t
+zix_hash_size(const ZixHash* hash);
+
+/**
+   Insert an item into `hash`.
+
+   If no matching value is found, ZIX_STATUS_SUCCESS will be returned, and @p
+   inserted will be pointed to the copy of `value` made in the new hash node.
+
+   If a matching value already exists, ZIX_STATUS_EXISTS will be returned, and
+   `inserted` will be pointed to the existing value.
+
+   @param hash The hash table.
+   @param value The value to be inserted.
+   @param inserted The copy of `value` in the hash table.
+   @return ZIX_STATUS_SUCCESS, ZIX_STATUS_EXISTS, or ZIX_STATUS_NO_MEM.
+*/
+ZIX_API
+ZixStatus
+zix_hash_insert(ZixHash* hash, const void* value, void** inserted);
+
+/**
+   Remove an item from `hash`.
+
+   @param hash The hash table.
+   @param value The value to remove.
+   @return ZIX_STATUS_SUCCES or ZIX_STATUS_NOT_FOUND.
+*/
+ZIX_API
+ZixStatus
+zix_hash_remove(ZixHash* hash, const void* value);
+
+/**
+   Search for an item in `hash`.
+
+   @param hash The hash table.
+   @param value The value to search for.
+*/
+ZIX_API
+void*
+zix_hash_find(const ZixHash* hash, const void* value);
+
+/**
+   Call `f` on each value in `hash`.
+
+   @param hash The hash table.
+   @param f The function to call on each value.
+   @param user_data The user_data parameter passed to `f`.
+*/
+ZIX_API
+void
+zix_hash_foreach(ZixHash* hash, ZixHashVisitFunc f, void* user_data);
+
+/**
+   @}
+   @}
+*/
+
+#ifdef __cplusplus
+} /* extern "C" */
+#endif
+
+#endif /* ZIX_HASH_H */