1 files changed, 50 insertions, 0 deletions
diff --git a/vendor/unicode-normalization/src/perfect_hash.rs b/vendor/unicode-normalization/src/perfect_hash.rs
new file mode 100644
index 000000000..3dbc16639
--- /dev/null
+++ b/vendor/unicode-normalization/src/perfect_hash.rs
@@ -0,0 +1,50 @@
+// Copyright 2019 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+//! Support for lookups based on minimal perfect hashing.
+
+// This function is based on multiplication being fast and is "good enough". Also
+// it can share some work between the unsalted and salted versions.
+#[inline]
+fn my_hash(key: u32, salt: u32, n: usize) -> usize {
+    let y = key.wrapping_add(salt).wrapping_mul(2654435769);
+    let y = y ^ key.wrapping_mul(0x31415926);
+    (((y as u64) * (n as u64)) >> 32) as usize
+}
+
+/// Do a lookup using minimal perfect hashing.
+///
+/// The table is stored as a sequence of "salt" values, then a sequence of
+/// values that contain packed key/value pairs. The strategy is to hash twice.
+/// The first hash retrieves a salt value that makes the second hash unique.
+/// The hash function doesn't have to be very good, just good enough that the
+/// resulting map is unique.
+#[inline]
+pub(crate) fn mph_lookup<KV, V, FK, FV>(
+    x: u32,
+    salt: &[u16],
+    kv: &[KV],
+    fk: FK,
+    fv: FV,
+    default: V,
+) -> V
+where
+    KV: Copy,
+    FK: Fn(KV) -> u32,
+    FV: Fn(KV) -> V,
+{
+    let s = salt[my_hash(x, 0, salt.len())] as u32;
+    let key_val = kv[my_hash(x, s, salt.len())];
+    if x == fk(key_val) {
+        fv(key_val)
+    } else {
+        default
+    }
+}