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34 lines
1.2 KiB
Rust
34 lines
1.2 KiB
Rust
/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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//! This file stolen wholesale from rustc/src/librustc/util/nodemap.rs
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use std::default::Default;
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use std::hash::Hasher;
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use std::num::wrapping::WrappingOps;
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/// A speedy hash algorithm for node ids and def ids. The hashmap in
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/// libcollections by default uses SipHash which isn't quite as speedy as we
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/// want. In the compiler we're not really worried about DOS attempts, so we
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/// just default to a non-cryptographic hash.
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///
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/// This uses FNV hashing, as described here:
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/// http://en.wikipedia.org/wiki/Fowler%E2%80%93Noll%E2%80%93Vo_hash_function
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pub struct FnvHasher(u64);
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impl Default for FnvHasher {
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fn default() -> FnvHasher { FnvHasher(0xcbf29ce484222325) }
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}
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impl Hasher for FnvHasher {
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fn finish(&self) -> u64 { self.0 }
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fn write(&mut self, bytes: &[u8]) {
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let FnvHasher(mut hash) = *self;
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for byte in bytes.iter() {
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hash = hash ^ (*byte as u64);
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hash = hash.wrapping_mul(0x100000001b3);
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}
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*self = FnvHasher(hash);
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}
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}
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