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diff --git a/src/zix/hash.h b/src/zix/hash.h
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+/*
+  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 */