Vendor dependencies

Let's see how I like this workflow.

vendor/cxx/src/sip.rs

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+// Vendored from libstd:
+// https://github.com/rust-lang/rust/blob/1.57.0/library/core/src/hash/sip.rs
+//
+// TODO: maybe depend on a hasher from crates.io if this becomes annoying to
+// maintain, or change this to a simpler one.
+
+#![cfg(not(feature = "std"))]
+
+use core::cmp;
+use core::hash::Hasher;
+use core::mem;
+use core::ptr;
+
+/// An implementation of SipHash 1-3.
+///
+/// This is currently the default hashing function used by standard library
+/// (e.g., `collections::HashMap` uses it by default).
+///
+/// See: <https://131002.net/siphash>
+pub struct SipHasher13 {
+    k0: u64,
+    k1: u64,
+    length: usize, // how many bytes we've processed
+    state: State,  // hash State
+    tail: u64,     // unprocessed bytes le
+    ntail: usize,  // how many bytes in tail are valid
+}
+
+#[derive(Clone, Copy)]
+#[repr(C)]
+struct State {
+    // v0, v2 and v1, v3 show up in pairs in the algorithm,
+    // and simd implementations of SipHash will use vectors
+    // of v02 and v13. By placing them in this order in the struct,
+    // the compiler can pick up on just a few simd optimizations by itself.
+    v0: u64,
+    v2: u64,
+    v1: u64,
+    v3: u64,
+}
+
+macro_rules! compress {
+    ($state:expr) => {
+        compress!($state.v0, $state.v1, $state.v2, $state.v3)
+    };
+    ($v0:expr, $v1:expr, $v2:expr, $v3:expr) => {
+        $v0 = $v0.wrapping_add($v1);
+        $v1 = $v1.rotate_left(13);
+        $v1 ^= $v0;
+        $v0 = $v0.rotate_left(32);
+        $v2 = $v2.wrapping_add($v3);
+        $v3 = $v3.rotate_left(16);
+        $v3 ^= $v2;
+        $v0 = $v0.wrapping_add($v3);
+        $v3 = $v3.rotate_left(21);
+        $v3 ^= $v0;
+        $v2 = $v2.wrapping_add($v1);
+        $v1 = $v1.rotate_left(17);
+        $v1 ^= $v2;
+        $v2 = $v2.rotate_left(32);
+    };
+}
+
+/// Loads an integer of the desired type from a byte stream, in LE order. Uses
+/// `copy_nonoverlapping` to let the compiler generate the most efficient way
+/// to load it from a possibly unaligned address.
+///
+/// Unsafe because: unchecked indexing at i..i+size_of(int_ty)
+macro_rules! load_int_le {
+    ($buf:expr, $i:expr, $int_ty:ident) => {{
+        debug_assert!($i + mem::size_of::<$int_ty>() <= $buf.len());
+        let mut data = 0 as $int_ty;
+        ptr::copy_nonoverlapping(
+            $buf.as_ptr().add($i),
+            &mut data as *mut _ as *mut u8,
+            mem::size_of::<$int_ty>(),
+        );
+        data.to_le()
+    }};
+}
+
+/// Loads a u64 using up to 7 bytes of a byte slice. It looks clumsy but the
+/// `copy_nonoverlapping` calls that occur (via `load_int_le!`) all have fixed
+/// sizes and avoid calling `memcpy`, which is good for speed.
+///
+/// Unsafe because: unchecked indexing at start..start+len
+unsafe fn u8to64_le(buf: &[u8], start: usize, len: usize) -> u64 {
+    debug_assert!(len < 8);
+    let mut i = 0; // current byte index (from LSB) in the output u64
+    let mut out = 0;
+    if i + 3 < len {
+        // SAFETY: `i` cannot be greater than `len`, and the caller must guarantee
+        // that the index start..start+len is in bounds.
+        out = unsafe { load_int_le!(buf, start + i, u32) } as u64;
+        i += 4;
+    }
+    if i + 1 < len {
+        // SAFETY: same as above.
+        out |= (unsafe { load_int_le!(buf, start + i, u16) } as u64) << (i * 8);
+        i += 2
+    }
+    if i < len {
+        // SAFETY: same as above.
+        out |= (unsafe { *buf.get_unchecked(start + i) } as u64) << (i * 8);
+        i += 1;
+    }
+    debug_assert_eq!(i, len);
+    out
+}
+
+impl SipHasher13 {
+    /// Creates a new `SipHasher13` with the two initial keys set to 0.
+    pub fn new() -> Self {
+        Self::new_with_keys(0, 0)
+    }
+
+    /// Creates a `SipHasher13` that is keyed off the provided keys.
+    fn new_with_keys(key0: u64, key1: u64) -> Self {
+        let mut state = SipHasher13 {
+            k0: key0,
+            k1: key1,
+            length: 0,
+            state: State {
+                v0: 0,
+                v1: 0,
+                v2: 0,
+                v3: 0,
+            },
+            tail: 0,
+            ntail: 0,
+        };
+        state.reset();
+        state
+    }
+
+    fn reset(&mut self) {
+        self.length = 0;
+        self.state.v0 = self.k0 ^ 0x736f6d6570736575;
+        self.state.v1 = self.k1 ^ 0x646f72616e646f6d;
+        self.state.v2 = self.k0 ^ 0x6c7967656e657261;
+        self.state.v3 = self.k1 ^ 0x7465646279746573;
+        self.ntail = 0;
+    }
+}
+
+impl Hasher for SipHasher13 {
+    // Note: no integer hashing methods (`write_u*`, `write_i*`) are defined
+    // for this type. We could add them, copy the `short_write` implementation
+    // in librustc_data_structures/sip128.rs, and add `write_u*`/`write_i*`
+    // methods to `SipHasher`, `SipHasher13`, and `DefaultHasher`. This would
+    // greatly speed up integer hashing by those hashers, at the cost of
+    // slightly slowing down compile speeds on some benchmarks. See #69152 for
+    // details.
+    fn write(&mut self, msg: &[u8]) {
+        let length = msg.len();
+        self.length += length;
+
+        let mut needed = 0;
+
+        if self.ntail != 0 {
+            needed = 8 - self.ntail;
+            // SAFETY: `cmp::min(length, needed)` is guaranteed to not be over `length`
+            self.tail |= unsafe { u8to64_le(msg, 0, cmp::min(length, needed)) } << (8 * self.ntail);
+            if length < needed {
+                self.ntail += length;
+                return;
+            } else {
+                self.state.v3 ^= self.tail;
+                Sip13Rounds::c_rounds(&mut self.state);
+                self.state.v0 ^= self.tail;
+                self.ntail = 0;
+            }
+        }
+
+        // Buffered tail is now flushed, process new input.
+        let len = length - needed;
+        let left = len & 0x7; // len % 8
+
+        let mut i = needed;
+        while i < len - left {
+            // SAFETY: because `len - left` is the biggest multiple of 8 under
+            // `len`, and because `i` starts at `needed` where `len` is `length - needed`,
+            // `i + 8` is guaranteed to be less than or equal to `length`.
+            let mi = unsafe { load_int_le!(msg, i, u64) };
+
+            self.state.v3 ^= mi;
+            Sip13Rounds::c_rounds(&mut self.state);
+            self.state.v0 ^= mi;
+
+            i += 8;
+        }
+
+        // SAFETY: `i` is now `needed + len.div_euclid(8) * 8`,
+        // so `i + left` = `needed + len` = `length`, which is by
+        // definition equal to `msg.len()`.
+        self.tail = unsafe { u8to64_le(msg, i, left) };
+        self.ntail = left;
+    }
+
+    fn finish(&self) -> u64 {
+        let mut state = self.state;
+
+        let b: u64 = ((self.length as u64 & 0xff) << 56) | self.tail;
+
+        state.v3 ^= b;
+        Sip13Rounds::c_rounds(&mut state);
+        state.v0 ^= b;
+
+        state.v2 ^= 0xff;
+        Sip13Rounds::d_rounds(&mut state);
+
+        state.v0 ^ state.v1 ^ state.v2 ^ state.v3
+    }
+}
+
+struct Sip13Rounds;
+
+impl Sip13Rounds {
+    fn c_rounds(state: &mut State) {
+        compress!(state);
+    }
+
+    fn d_rounds(state: &mut State) {
+        compress!(state);
+        compress!(state);
+        compress!(state);
+    }
+}