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// New BSD License // // Copyright © 2018-present, Michael Cummings <mgcummings@yahoo.com>. // All rights reserved. // // Redistribution and use in source and binary forms, with or without // modification, are permitted provided that the following conditions are met: // * Redistributions of source code must retain the above copyright notice, // this list of conditions and the following disclaimer. // * Redistributions in binary form must reproduce the above copyright // notice, this list of conditions and the following disclaimer in the // documentation and/or other materials provided with the distribution. // * Neither the name of the copyright holder nor the names of its // contributors may be used to endorse or promote products derived from // this software without specific prior written permission. // // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" // AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE // IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE // ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDERS AND CONTRIBUTORS BE // LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR // CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF // SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS // INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN // CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) // ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE // POSSIBILITY OF SUCH DAMAGE. // use std::hash::Hasher; use super::HasherU32; /// /// Implements 32 bit version of one of the original hash functions post by Daniel J. Bernstein. /// /// # Examples /// /// ```rust /// use std::hash::Hasher; /// use djb_hash::HasherU32; /// use djb_hash::x33a_u32::*; /// let input = "Ez"; /// let mut hasher = X33aU32::new(); /// hasher.write(&input.as_bytes()); /// assert_eq!(hasher.finish(), 5862308u64); /// assert_eq!(hasher.finish_u32(), 5862308u32); /// ``` /// Another example: /// /// ```rust /// # use std::hash::Hasher; /// # use djb_hash::HasherU32; /// # use djb_hash::x33a_u32::*; /// let input = "FY"; /// let mut hasher = X33aU32::new(); /// hasher.write(&input.as_bytes()); /// assert_eq!(hasher.finish(), 5862308u64); /// ``` /// /// These two examples show one of the known issues with this hash function: /// hash collision. Both strings hash to the same value. If it was being used in /// a public face HashMap it would open a possible DoS attack vector. Java, JS, /// Python and PHP have all experience these types of attacks when using this or /// other similar hash functions. /// /// Adding prefixes and/or suffixes will change the hash but not the collision. /// An example: /// /// ```rust /// # use std::hash::Hasher; /// # use djb_hash::x33a_u32::*; /// let input1 = "abcEzpie"; /// let input2 = "abcFYpie"; /// let mut hasher1 = X33aU32::new(); /// let mut hasher2 = X33aU32::new(); /// hasher1.write(&input1.as_bytes()); /// hasher2.write(&input2.as_bytes()); /// assert_eq!(hasher1.finish(), 1686394568u64); /// assert_eq!(hasher1.finish(), hasher2.finish()); /// ``` /// pub struct X33aU32 { hash: u32, } impl X33aU32 { /// /// Creates a new hash using the original 5381 prime number salt value used by DJB. /// pub fn new() -> Self { X33aU32 { hash: 5381 } } /// /// Creates a new hash using user supplied salt value. /// /// The supplied salt needs to be a prime number. It should have bits in /// more than just the lower 8 bits but setting any bits past half the size /// of the hash is of limited use as they are quickly lost during the /// multiplication stage for long values and tend to because static for very /// short values. Primes between 16 to 32 bits for 64 bit hashes seem to /// work best in most cases and between 16 to 24 bits for 32 bit hashes. /// /// # Examples /// /// ```rust /// use std::hash::Hasher; /// use djb_hash::HasherU32; /// use djb_hash::x33a_u32::*; /// let input = "Ez"; /// let mut hasher = X33aU32::new_with_salt(5381); /// hasher.write(&input.as_bytes()); /// assert_eq!(hasher.finish(), 5862308u64); /// assert_eq!(hasher.finish_u32(), 5862308u32); /// ``` /// /// Another example: /// /// ```rust /// # use std::hash::Hasher; /// # use djb_hash::HasherU32; /// # use djb_hash::x33a_u32::*; /// let input = "FY"; /// let mut hasher = X33aU32::new_with_salt(5387); /// hasher.write(&input.as_bytes()); /// assert_eq!(hasher.finish(), 5868842u64); /// assert_eq!(hasher.finish_u32(), 5868842u32); /// ``` /// /// These examples show how the hashes change with different salts but in /// the next example you can see the same strings, "Ez" and "FY", will still /// collide. /// /// ```rust /// # use std::hash::Hasher; /// # use djb_hash::HasherU32; /// # use djb_hash::x33a_u32::*; /// let input = "Ez"; /// let mut hasher = X33aU32::new_with_salt(5387); /// hasher.write(&input.as_bytes()); /// assert_eq!(hasher.finish(), 5868842u64); /// ``` /// pub fn new_with_salt(s: u32) -> Self { X33aU32 { hash: s } } } impl HasherU32 for X33aU32 { /// /// # Examples /// /// ```rust /// # use std::hash::Hasher; /// # use djb_hash::x33a::*; /// let input = "FY"; /// let mut hasher = X33a::new(); /// hasher.write(&input.as_bytes()); /// assert_eq!(hasher.finish(), 5862308u64); /// ``` /// fn finish_u32(&self) -> u32 { self.hash } } impl Hasher for X33aU32 { fn finish(&self) -> u64 { self.hash as u64 } /// /// Writes byte slice to hash. /// /// Does hash * 33 + byte but is implemented as hash << 5 (*32) + hash + byte as this is faster /// on most processors vs normal multiplication. /// fn write(&mut self, bytes: &[u8]) { for byte in bytes { self.hash = (self.hash << 5).wrapping_add(self.hash).wrapping_add(*byte as u32); } } } #[cfg(test)] mod tests { use std::hash::Hasher; use super::*; #[test] fn it_does_hash_correctly() { let mut sut = X33aU32::new(); let input = [69, 122]; sut.write(&input); assert_eq!(sut.finish(), 5862308u64); let mut sut = X33aU32::new(); let input = [70, 89]; sut.write(&input); assert_eq!(sut.finish(), 5862308u64); let input = "abcEzpie"; let mut sut = X33aU32::new_with_salt(5381); sut.write(&input.as_bytes()); assert_eq!(sut.finish(), 1686394568u64); assert_eq!(sut.finish_u32(), 1686394568u32); } }