Adding upstream version 115.7.0esr.upstream/115.7.0esrupstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 417 insertions, 0 deletions

diff --git a/mfbt/HashFunctions.h b/mfbt/HashFunctions.h
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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/* Utilities for hashing. */
+
+/*
+ * This file exports functions for hashing data down to a uint32_t (a.k.a.
+ * mozilla::HashNumber), including:
+ *
+ *  - HashString    Hash a char* or char16_t/wchar_t* of known or unknown
+ *                  length.
+ *
+ *  - HashBytes     Hash a byte array of known length.
+ *
+ *  - HashGeneric   Hash one or more values.  Currently, we support uint32_t,
+ *                  types which can be implicitly cast to uint32_t, data
+ *                  pointers, and function pointers.
+ *
+ *  - AddToHash     Add one or more values to the given hash.  This supports the
+ *                  same list of types as HashGeneric.
+ *
+ *
+ * You can chain these functions together to hash complex objects.  For example:
+ *
+ *  class ComplexObject
+ *  {
+ *    char* mStr;
+ *    uint32_t mUint1, mUint2;
+ *    void (*mCallbackFn)();
+ *
+ *  public:
+ *    HashNumber hash()
+ *    {
+ *      HashNumber hash = HashString(mStr);
+ *      hash = AddToHash(hash, mUint1, mUint2);
+ *      return AddToHash(hash, mCallbackFn);
+ *    }
+ *  };
+ *
+ * If you want to hash an nsAString or nsACString, use the HashString functions
+ * in nsHashKeys.h.
+ */
+
+#ifndef mozilla_HashFunctions_h
+#define mozilla_HashFunctions_h
+
+#include "mozilla/Assertions.h"
+#include "mozilla/Attributes.h"
+#include "mozilla/Char16.h"
+#include "mozilla/MathAlgorithms.h"
+#include "mozilla/Types.h"
+#include "mozilla/WrappingOperations.h"
+
+#include <stdint.h>
+#include <type_traits>
+
+namespace mozilla {
+
+using HashNumber = uint32_t;
+static const uint32_t kHashNumberBits = 32;
+
+/**
+ * The golden ratio as a 32-bit fixed-point value.
+ */
+static const HashNumber kGoldenRatioU32 = 0x9E3779B9U;
+
+/*
+ * Given a raw hash code, h, return a number that can be used to select a hash
+ * bucket.
+ *
+ * This function aims to produce as uniform an output distribution as possible,
+ * especially in the most significant (leftmost) bits, even though the input
+ * distribution may be highly nonrandom, given the constraints that this must
+ * be deterministic and quick to compute.
+ *
+ * Since the leftmost bits of the result are best, the hash bucket index is
+ * computed by doing ScrambleHashCode(h) / (2^32/N) or the equivalent
+ * right-shift, not ScrambleHashCode(h) % N or the equivalent bit-mask.
+ */
+constexpr HashNumber ScrambleHashCode(HashNumber h) {
+  /*
+   * Simply returning h would not cause any hash tables to produce wrong
+   * answers. But it can produce pathologically bad performance: The caller
+   * right-shifts the result, keeping only the highest bits. The high bits of
+   * hash codes are very often completely entropy-free. (So are the lowest
+   * bits.)
+   *
+   * So we use Fibonacci hashing, as described in Knuth, The Art of Computer
+   * Programming, 6.4. This mixes all the bits of the input hash code h.
+   *
+   * The value of goldenRatio is taken from the hex expansion of the golden
+   * ratio, which starts 1.9E3779B9.... This value is especially good if
+   * values with consecutive hash codes are stored in a hash table; see Knuth
+   * for details.
+   */
+  return mozilla::WrappingMultiply(h, kGoldenRatioU32);
+}
+
+namespace detail {
+
+MOZ_NO_SANITIZE_UNSIGNED_OVERFLOW
+constexpr HashNumber RotateLeft5(HashNumber aValue) {
+  return (aValue << 5) | (aValue >> 27);
+}
+
+constexpr HashNumber AddU32ToHash(HashNumber aHash, uint32_t aValue) {
+  /*
+   * This is the meat of all our hash routines.  This hash function is not
+   * particularly sophisticated, but it seems to work well for our mostly
+   * plain-text inputs.  Implementation notes follow.
+   *
+   * Our use of the golden ratio here is arbitrary; we could pick almost any
+   * number which:
+   *
+   *  * is odd (because otherwise, all our hash values will be even)
+   *
+   *  * has a reasonably-even mix of 1's and 0's (consider the extreme case
+   *    where we multiply by 0x3 or 0xeffffff -- this will not produce good
+   *    mixing across all bits of the hash).
+   *
+   * The rotation length of 5 is also arbitrary, although an odd number is again
+   * preferable so our hash explores the whole universe of possible rotations.
+   *
+   * Finally, we multiply by the golden ratio *after* xor'ing, not before.
+   * Otherwise, if |aHash| is 0 (as it often is for the beginning of a
+   * message), the expression
+   *
+   *   mozilla::WrappingMultiply(kGoldenRatioU32, RotateLeft5(aHash))
+   *   |xor|
+   *   aValue
+   *
+   * evaluates to |aValue|.
+   *
+   * (Number-theoretic aside: Because any odd number |m| is relatively prime to
+   * our modulus (2**32), the list
+   *
+   *    [x * m (mod 2**32) for 0 <= x < 2**32]
+   *
+   * has no duplicate elements.  This means that multiplying by |m| does not
+   * cause us to skip any possible hash values.
+   *
+   * It's also nice if |m| has large-ish order mod 2**32 -- that is, if the
+   * smallest k such that m**k == 1 (mod 2**32) is large -- so we can safely
+   * multiply our hash value by |m| a few times without negating the
+   * multiplicative effect.  Our golden ratio constant has order 2**29, which is
+   * more than enough for our purposes.)
+   */
+  return mozilla::WrappingMultiply(kGoldenRatioU32,
+                                   RotateLeft5(aHash) ^ aValue);
+}
+
+/**
+ * AddUintptrToHash takes sizeof(uintptr_t) as a template parameter.
+ */
+template <size_t PtrSize>
+constexpr HashNumber AddUintptrToHash(HashNumber aHash, uintptr_t aValue) {
+  return AddU32ToHash(aHash, static_cast<uint32_t>(aValue));
+}
+
+template <>
+inline HashNumber AddUintptrToHash<8>(HashNumber aHash, uintptr_t aValue) {
+  uint32_t v1 = static_cast<uint32_t>(aValue);
+  uint32_t v2 = static_cast<uint32_t>(static_cast<uint64_t>(aValue) >> 32);
+  return AddU32ToHash(AddU32ToHash(aHash, v1), v2);
+}
+
+} /* namespace detail */
+
+/**
+ * AddToHash takes a hash and some values and returns a new hash based on the
+ * inputs.
+ *
+ * Currently, we support hashing uint32_t's, values which we can implicitly
+ * convert to uint32_t, data pointers, and function pointers.
+ */
+template <typename T, bool TypeIsNotIntegral = !std::is_integral_v<T>,
+          bool TypeIsNotEnum = !std::is_enum_v<T>,
+          std::enable_if_t<TypeIsNotIntegral && TypeIsNotEnum, int> = 0>
+[[nodiscard]] inline HashNumber AddToHash(HashNumber aHash, T aA) {
+  /*
+   * Try to convert |A| to uint32_t implicitly.  If this works, great.  If not,
+   * we'll error out.
+   */
+  return detail::AddU32ToHash(aHash, aA);
+}
+
+template <typename A>
+[[nodiscard]] inline HashNumber AddToHash(HashNumber aHash, A* aA) {
+  /*
+   * You might think this function should just take a void*.  But then we'd only
+   * catch data pointers and couldn't handle function pointers.
+   */
+
+  static_assert(sizeof(aA) == sizeof(uintptr_t), "Strange pointer!");
+
+  return detail::AddUintptrToHash<sizeof(uintptr_t)>(aHash, uintptr_t(aA));
+}
+
+// We use AddUintptrToHash() for hashing all integral types.  8-byte integral
+// types are treated the same as 64-bit pointers, and smaller integral types are
+// first implicitly converted to 32 bits and then passed to AddUintptrToHash()
+// to be hashed.
+template <typename T, std::enable_if_t<std::is_integral_v<T>, int> = 0>
+[[nodiscard]] constexpr HashNumber AddToHash(HashNumber aHash, T aA) {
+  return detail::AddUintptrToHash<sizeof(T)>(aHash, aA);
+}
+
+template <typename T, std::enable_if_t<std::is_enum_v<T>, int> = 0>
+[[nodiscard]] constexpr HashNumber AddToHash(HashNumber aHash, T aA) {
+  // Hash using AddUintptrToHash with the underlying type of the enum type
+  using UnderlyingType = typename std::underlying_type<T>::type;
+  return detail::AddUintptrToHash<sizeof(UnderlyingType)>(
+      aHash, static_cast<UnderlyingType>(aA));
+}
+
+template <typename A, typename... Args>
+[[nodiscard]] HashNumber AddToHash(HashNumber aHash, A aArg, Args... aArgs) {
+  return AddToHash(AddToHash(aHash, aArg), aArgs...);
+}
+
+/**
+ * The HashGeneric class of functions let you hash one or more values.
+ *
+ * If you want to hash together two values x and y, calling HashGeneric(x, y) is
+ * much better than calling AddToHash(x, y), because AddToHash(x, y) assumes
+ * that x has already been hashed.
+ */
+template <typename... Args>
+[[nodiscard]] inline HashNumber HashGeneric(Args... aArgs) {
+  return AddToHash(0, aArgs...);
+}
+
+/**
+ * Hash successive |*aIter| until |!*aIter|, i.e. til null-termination.
+ *
+ * This function is *not* named HashString like the non-template overloads
+ * below.  Some users define HashString overloads and pass inexactly-matching
+ * values to them -- but an inexactly-matching value would match this overload
+ * instead!  We follow the general rule and don't mix and match template and
+ * regular overloads to avoid this.
+ *
+ * If you have the string's length, call HashStringKnownLength: it may be
+ * marginally faster.
+ */
+template <typename Iterator>
+[[nodiscard]] constexpr HashNumber HashStringUntilZero(Iterator aIter) {
+  HashNumber hash = 0;
+  for (; auto c = *aIter; ++aIter) {
+    hash = AddToHash(hash, c);
+  }
+  return hash;
+}
+
+/**
+ * Hash successive |aIter[i]| up to |i == aLength|.
+ */
+template <typename Iterator>
+[[nodiscard]] constexpr HashNumber HashStringKnownLength(Iterator aIter,
+                                                         size_t aLength) {
+  HashNumber hash = 0;
+  for (size_t i = 0; i < aLength; i++) {
+    hash = AddToHash(hash, aIter[i]);
+  }
+  return hash;
+}
+
+/**
+ * The HashString overloads below do just what you'd expect.
+ *
+ * These functions are non-template functions so that users can 1) overload them
+ * with their own types 2) in a way that allows implicit conversions to happen.
+ */
+[[nodiscard]] inline HashNumber HashString(const char* aStr) {
+  // Use the |const unsigned char*| version of the above so that all ordinary
+  // character data hashes identically.
+  return HashStringUntilZero(reinterpret_cast<const unsigned char*>(aStr));
+}
+
+[[nodiscard]] inline HashNumber HashString(const char* aStr, size_t aLength) {
+  // Delegate to the |const unsigned char*| version of the above to share
+  // template instantiations.
+  return HashStringKnownLength(reinterpret_cast<const unsigned char*>(aStr),
+                               aLength);
+}
+
+[[nodiscard]] inline HashNumber HashString(const unsigned char* aStr,
+                                           size_t aLength) {
+  return HashStringKnownLength(aStr, aLength);
+}
+
+[[nodiscard]] constexpr HashNumber HashString(const char16_t* aStr) {
+  return HashStringUntilZero(aStr);
+}
+
+[[nodiscard]] inline HashNumber HashString(const char16_t* aStr,
+                                           size_t aLength) {
+  return HashStringKnownLength(aStr, aLength);
+}
+
+/**
+ * HashString overloads for |wchar_t| on platforms where it isn't |char16_t|.
+ */
+template <typename WCharT, typename = typename std::enable_if<
+                               std::is_same<WCharT, wchar_t>::value &&
+                               !std::is_same<wchar_t, char16_t>::value>::type>
+[[nodiscard]] inline HashNumber HashString(const WCharT* aStr) {
+  return HashStringUntilZero(aStr);
+}
+
+template <typename WCharT, typename = typename std::enable_if<
+                               std::is_same<WCharT, wchar_t>::value &&
+                               !std::is_same<wchar_t, char16_t>::value>::type>
+[[nodiscard]] inline HashNumber HashString(const WCharT* aStr, size_t aLength) {
+  return HashStringKnownLength(aStr, aLength);
+}
+
+/**
+ * Hash some number of bytes.
+ *
+ * This hash walks word-by-word, rather than byte-by-byte, so you won't get the
+ * same result out of HashBytes as you would out of HashString.
+ */
+[[nodiscard]] extern MFBT_API HashNumber HashBytes(const void* bytes,
+                                                   size_t aLength);
+
+/**
+ * A pseudorandom function mapping 32-bit integers to 32-bit integers.
+ *
+ * This is for when you're feeding private data (like pointer values or credit
+ * card numbers) to a non-crypto hash function (like HashBytes) and then using
+ * the hash code for something that untrusted parties could observe (like a JS
+ * Map). Plug in a HashCodeScrambler before that last step to avoid leaking the
+ * private data.
+ *
+ * By itself, this does not prevent hash-flooding DoS attacks, because an
+ * attacker can still generate many values with exactly equal hash codes by
+ * attacking the non-crypto hash function alone. Equal hash codes will, of
+ * course, still be equal however much you scramble them.
+ *
+ * The algorithm is SipHash-1-3. See <https://131002.net/siphash/>.
+ */
+class HashCodeScrambler {
+  struct SipHasher;
+
+  uint64_t mK0, mK1;
+
+ public:
+  /** Creates a new scrambler with the given 128-bit key. */
+  constexpr HashCodeScrambler(uint64_t aK0, uint64_t aK1)
+      : mK0(aK0), mK1(aK1) {}
+
+  /**
+   * Scramble a hash code. Always produces the same result for the same
+   * combination of key and hash code.
+   */
+  HashNumber scramble(HashNumber aHashCode) const {
+    SipHasher hasher(mK0, mK1);
+    return HashNumber(hasher.sipHash(aHashCode));
+  }
+
+  static constexpr size_t offsetOfMK0() {
+    return offsetof(HashCodeScrambler, mK0);
+  }
+
+  static constexpr size_t offsetOfMK1() {
+    return offsetof(HashCodeScrambler, mK1);
+  }
+
+ private:
+  struct SipHasher {
+    SipHasher(uint64_t aK0, uint64_t aK1) {
+      // 1. Initialization.
+      mV0 = aK0 ^ UINT64_C(0x736f6d6570736575);
+      mV1 = aK1 ^ UINT64_C(0x646f72616e646f6d);
+      mV2 = aK0 ^ UINT64_C(0x6c7967656e657261);
+      mV3 = aK1 ^ UINT64_C(0x7465646279746573);
+    }
+
+    uint64_t sipHash(uint64_t aM) {
+      // 2. Compression.
+      mV3 ^= aM;
+      sipRound();
+      mV0 ^= aM;
+
+      // 3. Finalization.
+      mV2 ^= 0xff;
+      for (int i = 0; i < 3; i++) sipRound();
+      return mV0 ^ mV1 ^ mV2 ^ mV3;
+    }
+
+    void sipRound() {
+      mV0 = WrappingAdd(mV0, mV1);
+      mV1 = RotateLeft(mV1, 13);
+      mV1 ^= mV0;
+      mV0 = RotateLeft(mV0, 32);
+      mV2 = WrappingAdd(mV2, mV3);
+      mV3 = RotateLeft(mV3, 16);
+      mV3 ^= mV2;
+      mV0 = WrappingAdd(mV0, mV3);
+      mV3 = RotateLeft(mV3, 21);
+      mV3 ^= mV0;
+      mV2 = WrappingAdd(mV2, mV1);
+      mV1 = RotateLeft(mV1, 17);
+      mV1 ^= mV2;
+      mV2 = RotateLeft(mV2, 32);
+    }
+
+    uint64_t mV0, mV1, mV2, mV3;
+  };
+};
+
+} /* namespace mozilla */
+
+#endif /* mozilla_HashFunctions_h */