whole-function comptime folding for zero-runtime value calls

std/hashmap/hashmap.hon

@@ -0,0 +1,160 @@
+import "@std/mem"
+
+PutError :: enum { key_exists }
+
+Entry func($K, $V type) type {
+	return struct {
+		# hash = 0 means empty
+		hash usize = 0
+		key K
+		value V
+	}
+}
+
+HashMap func(
+	$K, $V type,
+	$hash_key func(key K) usize,
+	$keys_eql func(a, b K) bool,
+) type {
+	return struct {
+		entries []mut Entry(K, V)
+		count usize
+		allocator mem.Allocator
+	}
+}
+
+StringHashMap func($V type) type {
+	return HashMap([]u8, V, str_hash, str_eql)
+}
+
+init func(
+	$K, $V type,
+	$hash_key func(key K) usize,
+	$keys_eql func(a, b K) bool,
+	allocator mem.Allocator,
+) HashMap(K, V, hash_key, keys_eql) {
+	return HashMap(K, V, hash_key, keys_eql){
+		entries = mem.empty(Entry(K, V)),
+		count = 0,
+		allocator = allocator,
+	}
+}
+
+#! free the entries in the hash map.
+#! note: this operation invalidates the map.
+deinit func(
+	$K, $V type,
+	$hash_key func(key K) usize,
+	$keys_eql func(a, b K) bool,
+	map @HashMap(K, V, hash_key, keys_eql),
+) void { mem.free(map.allocator, map.entries) }
+
+get func(
+	$K, $V type,
+	$hash_key func(key K) usize,
+	$keys_eql func(a, b K) bool,
+	map @HashMap(K, V, hash_key, keys_eql),
+	key K,
+) ?V {
+	if (map.count == 0) return null
+
+	hash :: normalize(hash_key(key))
+	idx usize = hash & (map.entries.len - 1)
+
+	while true {
+		entry :: map.entries[idx]
+		if (entry.hash == 0) return null
+
+		if (entry.hash == hash and keys_eql(entry.key, key)) {
+			return entry.value
+		}
+
+		idx = (idx + 1) & (map.entries.len - 1)
+	}
+}
+
+put func(
+	$K, $V type,
+	$hash_key func(key K) usize,
+	$keys_eql func(a, b K) bool,
+	map @mut HashMap(K, V, hash_key, keys_eql),
+	key K,
+	value V,
+) void ! (PutError | mem.AllocError) {
+	# check grow
+	threshold :: map.entries.len - divtrunc!(map.entries.len, 4)
+	if (map.entries.len == 0 or map.count + 1 > threshold) {
+		old_entries :: map.entries
+		new_size :: if (old_entries.len > 0) old_entries.len * 2 else 8
+		new_entries :: try mem.alloc(Entry(K, V), map.allocator, new_size)
+
+		# zero new entries
+		for 0..new_entries.len |i| {
+			new_entries[i].hash = 0
+		}
+
+		# move old entries
+		for old_entries |entry| {
+			if (entry.hash == 0) continue
+
+			# find an empty slot
+			idx usize = entry.hash & (new_entries.len - 1)
+			while new_entries[idx].hash != 0 {
+				idx = (idx + 1) & (new_entries.len - 1)
+			}
+
+			new_entries[idx] = entry
+		}
+
+		map.entries = new_entries
+		mem.free(map.allocator, old_entries)
+	}
+
+	# put new entry
+	hash :: normalize(hash_key(key))
+	idx usize = hash & (map.entries.len - 1)
+
+	while true {
+		entry :: map.entries[idx]
+		if entry.hash == 0 {
+			map.entries[idx] = Entry(K, V){
+				hash = hash,
+				key = key,
+				value = value,
+			}
+			map.count += 1
+			return
+		}
+
+		if (entry.hash == hash and keys_eql(entry.key, key)) {
+			return .key_exists
+		}
+
+		idx = (idx + 1) & (map.entries.len - 1)
+	}
+}
+
+hide normalize func(hash usize) usize {
+	# mapping both 0 and 1 to 1 is safe because equality resolves
+	# collisions (since hash and key must both be equal).
+	if (hash == 0) return 1
+	return hash
+}
+
+#! FNV-1a hash implementation.
+#! note: vulnerable to collision attacks.
+hide str_hash func(key []u8) usize {
+	hash u32 = 2166136261 # offset basis
+	prime u32 = 16777619
+
+	for key |byte| {
+		product u64 :: u64(hash xor u32(byte)) * prime
+		hash = u32(product & u64(maxval!(u32)))
+	}
+
+	return usize(hash)
+}
+
+hide str_eql func(a, b []u8) bool {
+	return mem.eql(a, b)
+}