Add best::table, a hash table implementation

.bazelrc

@@ -1,2 +1,3 @@
 # Makes bazel test always print errors.
-test --test_output=errors
+test --test_output=errors
+build --copt=-ftemplate-backtrace-limit=0

.clangd

@@ -0,0 +1,2 @@
+CompileFlags:
+  Add: ['-march=native']

best/base/BUILD

@@ -25,6 +25,11 @@ cc_library(
   deps = [":macro"],
 )
 
+cc_library(
+  name = "arch",
+  hdrs = ["arch.h"],
+)
+
 cc_library(
   name = "macro",
   hdrs = [

best/base/arch.h

@@ -0,0 +1,109 @@
+/* //-*- C++ -*-///////////////////////////////////////////////////////////// *\
+
+  Copyright 2024
+  Miguel Young de la Sota and the Best Contributors 🧶🐈‍⬛
+
+  Licensed under the Apache License, Version 2.0 (the "License"); you may not
+  use this file except in compliance with the License. You may obtain a copy
+  of the License at
+
+                https://www.apache.org/licenses/LICENSE-2.0
+
+  Unless required by applicable law or agreed to in writing, software
+  distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+  License for the specific language governing permissions and limitations
+  under the License.
+
+\* ////////////////////////////////////////////////////////////////////////// */
+
+#ifndef BEST_BASE_INTRINSICS_H_
+#define BEST_BASE_INTRINSICS_H_
+
+//! Helpers for working with vendor intrinsics. This file will include all
+//! the relevant intrinsics headers *and* will define macros for detecting what
+//! features are statically available.
+//!
+//! Every macro is always defined; they should be used with `#if`, not `#ifdef`.
+
+/// # `BEST_X86`
+///
+/// True if we're targeting `x86_64`.
+#ifdef __x86_64__
+#define BEST_X86 1
+#else
+#define BEST_X86 0
+#endif
+
+/// # `BEST_AARCH64`
+///
+/// True if we're targeting `aarch64`.
+#ifdef __aarch64__
+#define BEST_AARCH64 1
+#else
+#define BEST_AARCH64 0
+#endif
+
+#if !(BEST_X86 || BEST_AARCH64)
+#error "unsupported architecture :("
+#endif
+
+/// # `BEST_SSE`, `BEST_SSE2`, `BEST_SSE3`, `BEST_SSSE3`
+/// # `BEST_SSE41`, `BEST_SSE42`, `BEST_SSE4A`
+///
+/// True if the named x86 extension is statically available.
+#ifdef __SSE__
+#define BEST_SSE 1
+#else
+#define BEST_SSE 0
+#endif
+#ifdef __SSE2__
+#define BEST_SSE2 1
+#else
+#define BEST_SSE2 0
+#endif
+#ifdef __SSE3__
+#define BEST_SSE3 1
+#else
+#define BEST_SSE3 0
+#endif
+#ifdef __SSSE3__
+#define BEST_SSSE3 1
+#else
+#define BEST_SSSE3 0
+#endif
+#ifdef __SSE4_1__
+#define BEST_SSE41 1
+#else
+#define BEST_SSE41 0
+#endif
+#ifdef __SSE4_2__
+#define BEST_SSE42 1
+#else
+#define BEST_SSE42 0
+#endif
+#ifdef __SSE4A__
+#define BEST_SSE4A 1
+#else
+#define BEST_SSE4A 0
+#endif
+
+/// # `BEST_AVX`, `BEST_AVX2`
+///
+/// True if the named x86 extension is statically available.
+#ifdef __AVX__
+#define BEST_AVX 1
+#else
+#define BEST_AVX 0
+#endif
+#ifdef __AVX2__
+#define BEST_AVX2 1
+#else
+#define BEST_AVX2 0
+#endif
+
+#if BEST_X86
+#include <x86intrin.h>
+#endif // BEST_X86
+
+#endif  // BEST_BASE_INTRINSICS_H_

best/base/fwd.h

@@ -190,6 +190,10 @@ struct access;
 namespace dyn_internal {
 struct access;
 }
+namespace format_internal {
+template <typename, typename...>
+class templ;
+}
 }  // namespace best
 
 #endif  // BEST_BASE_FWD_H_

best/base/hint.h

@@ -106,6 +106,33 @@ BEST_INLINE_ALWAYS constexpr void assume(bool truth) {
   if (!std::is_constant_evaluated()) { asm volatile("" ::"m,r"(value)); }
   return decltype(value)(value);
 }
+
+/// # `best::prefetch_locality`
+///
+/// A locality value for a prefetch operation. Specifies which cache the
+/// prefetched memory should stick around in.
+enum class prefetch_locality {
+  Nontemporal = 0,
+  L3 = 1,
+  L2 = 2,
+  L1 = 3,
+};
+
+/// # `best::prefetch_for_read()`, `best::prefetch_for_write()`
+///
+/// Prefetches the given memory.
+template <best::prefetch_locality locality = best::prefetch_locality::L1>
+BEST_INLINE_SYNTHETIC constexpr void prefetch_for_read(const void* addr) {
+  if (!std::is_constant_evaluated()) {
+    __builtin_prefetch(addr, 0, int(locality));
+  }
+}
+template <best::prefetch_locality locality = best::prefetch_locality::L1>
+BEST_INLINE_SYNTHETIC constexpr void prefetch_for_write(const void* addr) {
+  if (!std::is_constant_evaluated()) {
+    __builtin_prefetch(addr, 1, int(locality));
+  }
+}
 }  // namespace best
 
 #endif  // BEST_BASE_HINT_H_

best/container/BUILD

@@ -10,6 +10,7 @@ cc_library(
     ":pun",
     "//best/base:port",
     "//best/base:tags",
+    "//best/hash",
     "//best/log/internal:crash",
   ],
 )
@@ -31,6 +32,7 @@ cc_library(
   deps = [
     "//best/base:ord",
     "//best/memory:ptr",
+    "//best/hash",
   ]
 )
 
@@ -49,6 +51,7 @@ cc_library(
   hdrs = ["option.h"],
   deps = [
     ":choice",
+    "//best/hash",
     "//best/log/internal:crash",
   ],
 )
@@ -97,6 +100,7 @@ cc_library(
   deps = [
     ":choice",
     ":row",
+    "//best/hash",
     "//best/log/internal:crash",
   ],
 )
@@ -122,6 +126,7 @@ cc_library(
   ],
   deps = [
     ":object",
+    "//best/hash",
     "//best/base:port",
     "//best/base:tags",
   ],
@@ -143,6 +148,7 @@ cc_library(
   hdrs = ["box.h"],
   deps = [
     "//best/func:dyn",
+    "//best/hash",
     "//best/memory:allocator",
     "//best/memory:ptr",
   ]
@@ -187,6 +193,36 @@ cc_test(
     "//best/test:fodder",
   ],
 )
+hash
+cc_library(
+  name = "table",
+  hdrs = [
+    "table.h",
+    "internal/table.h",
+  ],
+  deps = [
+    ":option",
+    "//best/base:arch",
+    "//best/hash",
+    "//best/hash:fxhash",
+    "//best/hash:impls",
+    "//best/memory:allocator",
+    "//best/memory:span",
+    "//best/memory:layout",
+    "//best/meta/traits:pairs",
+  ],
+)
+
+cc_test(
+  name = "table_test",
+  srcs = ["table_test.cc"],
+  linkopts = ["-rdynamic"],
+  deps = [
+    ":table",
+    "//best/test",
+    "//best/test:fodder",
+  ],
+)
 
 cc_library(
   name = "simple_option",

best/container/box.h

@@ -26,6 +26,7 @@
 #include "best/container/object.h"
 #include "best/container/option.h"
 #include "best/func/dyn.h"
+#include "best/hash/hash.h"
 #include "best/memory/allocator.h"
 #include "best/memory/layout.h"
 #include "best/memory/ptr.h"
@@ -260,6 +261,13 @@ class BEST_RELOCATABLE box final {
     };
   }
 
+  template <best::hash_state State>
+  constexpr friend void BestHash(best::hasher<State>& h, const box& value)
+    requires requires { h.write(*value); }
+  {
+    h.write(*value);
+  }
+
   template <typename U>
   constexpr bool operator==(const best::box<U>& that) const
     requires best::equatable<best::view<T>, best::view<U>>

best/container/choice.h

@@ -25,9 +25,11 @@
 #include "best/base/ord.h"
 #include "best/base/tags.h"
 #include "best/container/internal/choice.h"
+#include "best/hash/hash.h"
 #include "best/log/internal/crash.h"
 #include "best/log/location.h"
 #include "best/meta/init.h"
+#include "best/meta/traits/empty.h"
 
 //! A sum type, like `std::variant`.
 //!
@@ -329,6 +331,14 @@ class choice final {
     };
   }
 
+  template <best::hash_state State>
+  constexpr friend void BestHash(best::hasher<State>& h, const choice& value)
+    requires (best::hashable<Alts> && ...)
+  {
+    value.index_match(
+      [&](auto idx, const auto& value) { h.write(idx.value, value); });
+  }
+
   // Comparisons.
   template <typename... Us>
   BEST_INLINE_ALWAYS constexpr bool operator==(const choice<Us...>& that) const