1 files changed, 392 insertions, 0 deletions
diff --git a/third_party/rust/ahash/src/fallback_hash.rs b/third_party/rust/ahash/src/fallback_hash.rs
new file mode 100644
index 0000000000..aad9efc859
--- /dev/null
+++ b/third_party/rust/ahash/src/fallback_hash.rs
@@ -0,0 +1,392 @@
+use crate::convert::*;
+use crate::operations::folded_multiply;
+use crate::operations::read_small;
+use crate::random_state::PI;
+use crate::RandomState;
+use core::hash::Hasher;
+
+///This constant come from Kunth's prng (Empirically it works better than those from splitmix32).
+pub(crate) const MULTIPLE: u64 = 6364136223846793005;
+const ROT: u32 = 23; //17
+
+/// A `Hasher` for hashing an arbitrary stream of bytes.
+///
+/// Instances of [`AHasher`] represent state that is updated while hashing data.
+///
+/// Each method updates the internal state based on the new data provided. Once
+/// all of the data has been provided, the resulting hash can be obtained by calling
+/// `finish()`
+///
+/// [Clone] is also provided in case you wish to calculate hashes for two different items that
+/// start with the same data.
+///
+#[derive(Debug, Clone)]
+pub struct AHasher {
+    buffer: u64,
+    pad: u64,
+    extra_keys: [u64; 2],
+}
+
+impl AHasher {
+    /// Creates a new hasher keyed to the provided key.
+    #[inline]
+    #[allow(dead_code)] // Is not called if non-fallback hash is used.
+    pub fn new_with_keys(key1: u128, key2: u128) -> AHasher {
+        let pi: [u128; 2] = PI.convert();
+        let key1: [u64; 2] = (key1 ^ pi[0]).convert();
+        let key2: [u64; 2] = (key2 ^ pi[1]).convert();
+        AHasher {
+            buffer: key1[0],
+            pad: key1[1],
+            extra_keys: key2,
+        }
+    }
+
+    #[allow(unused)] // False positive
+    pub(crate) fn test_with_keys(key1: u128, key2: u128) -> Self {
+        let key1: [u64; 2] = key1.convert();
+        let key2: [u64; 2] = key2.convert();
+        Self {
+            buffer: key1[0],
+            pad: key1[1],
+            extra_keys: key2,
+        }
+    }
+
+    #[inline]
+    #[allow(dead_code)] // Is not called if non-fallback hash is used.
+    pub(crate) fn from_random_state(rand_state: &RandomState) -> AHasher {
+        AHasher {
+            buffer: rand_state.k0,
+            pad: rand_state.k1,
+            extra_keys: [rand_state.k2, rand_state.k3],
+        }
+    }
+
+    /// This update function has the goal of updating the buffer with a single multiply
+    /// FxHash does this but is vulnerable to attack. To avoid this input needs to be masked to with an
+    /// unpredictable value. Other hashes such as murmurhash have taken this approach but were found vulnerable
+    /// to attack. The attack was based on the idea of reversing the pre-mixing (Which is necessarily
+    /// reversible otherwise bits would be lost) then placing a difference in the highest bit before the
+    /// multiply used to mix the data. Because a multiply can never affect the bits to the right of it, a
+    /// subsequent update that also differed in this bit could result in a predictable collision.
+    ///
+    /// This version avoids this vulnerability while still only using a single multiply. It takes advantage
+    /// of the fact that when a 64 bit multiply is performed the upper 64 bits are usually computed and thrown
+    /// away. Instead it creates two 128 bit values where the upper 64 bits are zeros and multiplies them.
+    /// (The compiler is smart enough to turn this into a 64 bit multiplication in the assembly)
+    /// Then the upper bits are xored with the lower bits to produce a single 64 bit result.
+    ///
+    /// To understand why this is a good scrambling function it helps to understand multiply-with-carry PRNGs:
+    /// https://en.wikipedia.org/wiki/Multiply-with-carry_pseudorandom_number_generator
+    /// If the multiple is chosen well, this creates a long period, decent quality PRNG.
+    /// Notice that this function is equivalent to this except the `buffer`/`state` is being xored with each
+    /// new block of data. In the event that data is all zeros, it is exactly equivalent to a MWC PRNG.
+    ///
+    /// This is impervious to attack because every bit buffer at the end is dependent on every bit in
+    /// `new_data ^ buffer`. For example suppose two inputs differed in only the 5th bit. Then when the
+    /// multiplication is performed the `result` will differ in bits 5-69. More specifically it will differ by
+    /// 2^5 * MULTIPLE. However in the next step bits 65-128 are turned into a separate 64 bit value. So the
+    /// differing bits will be in the lower 6 bits of this value. The two intermediate values that differ in
+    /// bits 5-63 and in bits 0-5 respectively get added together. Producing an output that differs in every
+    /// bit. The addition carries in the multiplication and at the end additionally mean that the even if an
+    /// attacker somehow knew part of (but not all) the contents of the buffer before hand,
+    /// they would not be able to predict any of the bits in the buffer at the end.
+    #[inline(always)]
+    #[cfg(feature = "folded_multiply")]
+    fn update(&mut self, new_data: u64) {
+        self.buffer = folded_multiply(new_data ^ self.buffer, MULTIPLE);
+    }
+
+    #[inline(always)]
+    #[cfg(not(feature = "folded_multiply"))]
+    fn update(&mut self, new_data: u64) {
+        let d1 = (new_data ^ self.buffer).wrapping_mul(MULTIPLE);
+        self.pad = (self.pad ^ d1).rotate_left(8).wrapping_mul(MULTIPLE);
+        self.buffer = (self.buffer ^ self.pad).rotate_left(24);
+    }
+
+    /// Similar to the above this function performs an update using a "folded multiply".
+    /// However it takes in 128 bits of data instead of 64. Both halves must be masked.
+    ///
+    /// This makes it impossible for an attacker to place a single bit difference between
+    /// two blocks so as to cancel each other.
+    ///
+    /// However this is not sufficient. to prevent (a,b) from hashing the same as (b,a) the buffer itself must
+    /// be updated between calls in a way that does not commute. To achieve this XOR and Rotate are used.
+    /// Add followed by xor is not the same as xor followed by add, and rotate ensures that the same out bits
+    /// can't be changed by the same set of input bits. To cancel this sequence with subsequent input would require
+    /// knowing the keys.
+    #[inline(always)]
+    #[cfg(feature = "folded_multiply")]
+    fn large_update(&mut self, new_data: u128) {
+        let block: [u64; 2] = new_data.convert();
+        let combined = folded_multiply(block[0] ^ self.extra_keys[0], block[1] ^ self.extra_keys[1]);
+        self.buffer = (self.buffer.wrapping_add(self.pad) ^ combined).rotate_left(ROT);
+    }
+
+    #[inline(always)]
+    #[cfg(not(feature = "folded_multiply"))]
+    fn large_update(&mut self, new_data: u128) {
+        let block: [u64; 2] = new_data.convert();
+        self.update(block[0] ^ self.extra_keys[0]);
+        self.update(block[1] ^ self.extra_keys[1]);
+    }
+
+    #[inline]
+    #[cfg(feature = "specialize")]
+    fn short_finish(&self) -> u64 {
+        self.buffer.wrapping_add(self.pad)
+    }
+}
+
+/// Provides [Hasher] methods to hash all of the primitive types.
+///
+/// [Hasher]: core::hash::Hasher
+impl Hasher for AHasher {
+    #[inline]
+    fn write_u8(&mut self, i: u8) {
+        self.update(i as u64);
+    }
+
+    #[inline]
+    fn write_u16(&mut self, i: u16) {
+        self.update(i as u64);
+    }
+
+    #[inline]
+    fn write_u32(&mut self, i: u32) {
+        self.update(i as u64);
+    }
+
+    #[inline]
+    fn write_u64(&mut self, i: u64) {
+        self.update(i as u64);
+    }
+
+    #[inline]
+    fn write_u128(&mut self, i: u128) {
+        self.large_update(i);
+    }
+
+    #[inline]
+    #[cfg(any(target_pointer_width = "64", target_pointer_width = "32", target_pointer_width = "16"))]
+    fn write_usize(&mut self, i: usize) {
+        self.write_u64(i as u64);
+    }
+
+    #[inline]
+    #[cfg(target_pointer_width = "128")]
+    fn write_usize(&mut self, i: usize) {
+        self.write_u128(i as u128);
+    }
+
+    #[inline]
+    #[allow(clippy::collapsible_if)]
+    fn write(&mut self, input: &[u8]) {
+        let mut data = input;
+        let length = data.len() as u64;
+        //Needs to be an add rather than an xor because otherwise it could be canceled with carefully formed input.
+        self.buffer = self.buffer.wrapping_add(length).wrapping_mul(MULTIPLE);
+        //A 'binary search' on sizes reduces the number of comparisons.
+        if data.len() > 8 {
+            if data.len() > 16 {
+                let tail = data.read_last_u128();
+                self.large_update(tail);
+                while data.len() > 16 {
+                    let (block, rest) = data.read_u128();
+                    self.large_update(block);
+                    data = rest;
+                }
+            } else {
+                self.large_update([data.read_u64().0, data.read_last_u64()].convert());
+            }
+        } else {
+            let value = read_small(data);
+            self.large_update(value.convert());
+        }
+    }
+
+    #[inline]
+    #[cfg(feature = "folded_multiply")]
+    fn finish(&self) -> u64 {
+        let rot = (self.buffer & 63) as u32;
+        folded_multiply(self.buffer, self.pad).rotate_left(rot)
+    }
+
+    #[inline]
+    #[cfg(not(feature = "folded_multiply"))]
+    fn finish(&self) -> u64 {
+        let rot = (self.buffer & 63) as u32;
+        (self.buffer.wrapping_mul(MULTIPLE) ^ self.pad).rotate_left(rot)
+    }
+}
+
+#[cfg(feature = "specialize")]
+pub(crate) struct AHasherU64 {
+    pub(crate) buffer: u64,
+    pub(crate) pad: u64,
+}
+
+/// A specialized hasher for only primitives under 64 bits.
+#[cfg(feature = "specialize")]
+impl Hasher for AHasherU64 {
+    #[inline]
+    fn finish(&self) -> u64 {
+        let rot = (self.pad & 63) as u32;
+        self.buffer.rotate_left(rot)
+    }
+
+    #[inline]
+    fn write(&mut self, _bytes: &[u8]) {
+        unreachable!("Specialized hasher was called with a different type of object")
+    }
+
+    #[inline]
+    fn write_u8(&mut self, i: u8) {
+        self.write_u64(i as u64);
+    }
+
+    #[inline]
+    fn write_u16(&mut self, i: u16) {
+        self.write_u64(i as u64);
+    }
+
+    #[inline]
+    fn write_u32(&mut self, i: u32) {
+        self.write_u64(i as u64);
+    }
+
+    #[inline]
+    fn write_u64(&mut self, i: u64) {
+        self.buffer = folded_multiply(i ^ self.buffer, MULTIPLE);
+    }
+
+    #[inline]
+    fn write_u128(&mut self, _i: u128) {
+        unreachable!("Specialized hasher was called with a different type of object")
+    }
+
+    #[inline]
+    fn write_usize(&mut self, _i: usize) {
+        unreachable!("Specialized hasher was called with a different type of object")
+    }
+}
+
+#[cfg(feature = "specialize")]
+pub(crate) struct AHasherFixed(pub AHasher);
+
+/// A specialized hasher for fixed size primitives larger than 64 bits.
+#[cfg(feature = "specialize")]
+impl Hasher for AHasherFixed {
+    #[inline]
+    fn finish(&self) -> u64 {
+        self.0.short_finish()
+    }
+
+    #[inline]
+    fn write(&mut self, bytes: &[u8]) {
+        self.0.write(bytes)
+    }
+
+    #[inline]
+    fn write_u8(&mut self, i: u8) {
+        self.write_u64(i as u64);
+    }
+
+    #[inline]
+    fn write_u16(&mut self, i: u16) {
+        self.write_u64(i as u64);
+    }
+
+    #[inline]
+    fn write_u32(&mut self, i: u32) {
+        self.write_u64(i as u64);
+    }
+
+    #[inline]
+    fn write_u64(&mut self, i: u64) {
+        self.0.write_u64(i);
+    }
+
+    #[inline]
+    fn write_u128(&mut self, i: u128) {
+        self.0.write_u128(i);
+    }
+
+    #[inline]
+    fn write_usize(&mut self, i: usize) {
+        self.0.write_usize(i);
+    }
+}
+
+#[cfg(feature = "specialize")]
+pub(crate) struct AHasherStr(pub AHasher);
+
+/// A specialized hasher for a single string
+/// Note that the other types don't panic because the hash impl for String tacks on an unneeded call. (As does vec)
+#[cfg(feature = "specialize")]
+impl Hasher for AHasherStr {
+    #[inline]
+    fn finish(&self) -> u64 {
+        self.0.finish()
+    }
+
+    #[inline]
+    fn write(&mut self, bytes: &[u8]) {
+        if bytes.len() > 8 {
+            self.0.write(bytes)
+        } else {
+            let value = read_small(bytes);
+            self.0.buffer = folded_multiply(value[0] ^ self.0.buffer,
+                                           value[1] ^ self.0.extra_keys[1]);
+            self.0.pad = self.0.pad.wrapping_add(bytes.len() as u64);
+        }
+    }
+
+    #[inline]
+    fn write_u8(&mut self, _i: u8) {}
+
+    #[inline]
+    fn write_u16(&mut self, _i: u16) {}
+
+    #[inline]
+    fn write_u32(&mut self, _i: u32) {}
+
+    #[inline]
+    fn write_u64(&mut self, _i: u64) {}
+
+    #[inline]
+    fn write_u128(&mut self, _i: u128) {}
+
+    #[inline]
+    fn write_usize(&mut self, _i: usize) {}
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::convert::Convert;
+    use crate::fallback_hash::*;
+
+    #[test]
+    fn test_hash() {
+        let mut hasher = AHasher::new_with_keys(0, 0);
+        let value: u64 = 1 << 32;
+        hasher.update(value);
+        let result = hasher.buffer;
+        let mut hasher = AHasher::new_with_keys(0, 0);
+        let value2: u64 = 1;
+        hasher.update(value2);
+        let result2 = hasher.buffer;
+        let result: [u8; 8] = result.convert();
+        let result2: [u8; 8] = result2.convert();
+        assert_ne!(hex::encode(result), hex::encode(result2));
+    }
+
+    #[test]
+    fn test_conversion() {
+        let input: &[u8] = "dddddddd".as_bytes();
+        let bytes: u64 = as_array!(input, 8).convert();
+        assert_eq!(bytes, 0x6464646464646464);
+    }
+}