1 files changed, 285 insertions, 0 deletions
diff --git a/js/src/vm/StaticStrings.h b/js/src/vm/StaticStrings.h
new file mode 100644
index 0000000000..4e8acf3036
--- /dev/null
+++ b/js/src/vm/StaticStrings.h
@@ -0,0 +1,285 @@
+/* -*- 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/. */
+
+#ifndef vm_StaticStrings_h
+#define vm_StaticStrings_h
+
+#include "mozilla/Assertions.h"  // MOZ_ASSERT
+#include "mozilla/Attributes.h"  // MOZ_ALWAYS_INLINE
+#include "mozilla/TextUtils.h"  // mozilla::{IsAsciiDigit, IsAsciiLowercaseAlpha, IsAsciiUppercaseAlpha}
+
+#include <stddef.h>     // size_t
+#include <stdint.h>     // int32_t, uint32_t
+#include <type_traits>  // std::is_same_v
+
+#include "jstypes.h"  // JS_PUBLIC_API, js::Bit, js::BitMask
+
+#include "js/TypeDecls.h"  // JS::Latin1Char
+
+struct JS_PUBLIC_API JSContext;
+
+class JSAtom;
+class JSLinearString;
+class JSString;
+
+namespace js {
+
+namespace frontend {
+class ParserAtomsTable;
+class TaggedParserAtomIndex;
+class WellKnownParserAtoms;
+struct CompilationAtomCache;
+}  // namespace frontend
+
+namespace jit {
+class MacroAssembler;
+}  // namespace jit
+
+class StaticStrings {
+  // NOTE: The WellKnownParserAtoms rely on these tables and may need to be
+  //       update if these tables are changed.
+  friend class js::frontend::ParserAtomsTable;
+  friend class js::frontend::TaggedParserAtomIndex;
+  friend class js::frontend::WellKnownParserAtoms;
+  friend struct js::frontend::CompilationAtomCache;
+
+  friend class js::jit::MacroAssembler;
+
+ private:
+  // Strings matches `[A-Za-z0-9$_]{2}` pattern.
+  // Store each character in 6 bits.
+  // See fromSmallChar/toSmallChar for the mapping.
+  static constexpr size_t SMALL_CHAR_BITS = 6;
+  static constexpr size_t SMALL_CHAR_MASK = js::BitMask(SMALL_CHAR_BITS);
+
+  // To optimize ASCII -> small char, allocate a table.
+  static constexpr size_t SMALL_CHAR_TABLE_SIZE = 128U;
+  static constexpr size_t NUM_SMALL_CHARS = js::Bit(SMALL_CHAR_BITS);
+  static constexpr size_t NUM_LENGTH2_ENTRIES =
+      NUM_SMALL_CHARS * NUM_SMALL_CHARS;
+
+ public:
+  /* We keep these public for the JITs. */
+  static const size_t UNIT_STATIC_LIMIT = 256U;
+  static const size_t INT_STATIC_LIMIT = 256U;
+
+ private:
+  JSAtom* length2StaticTable[NUM_LENGTH2_ENTRIES] = {};  // zeroes
+  JSAtom* unitStaticTable[UNIT_STATIC_LIMIT] = {};       // zeroes
+  JSAtom* intStaticTable[INT_STATIC_LIMIT] = {};         // zeroes
+
+ public:
+  StaticStrings() = default;
+
+  bool init(JSContext* cx);
+
+  static bool hasUint(uint32_t u) { return u < INT_STATIC_LIMIT; }
+
+  JSAtom* getUint(uint32_t u) {
+    MOZ_ASSERT(hasUint(u));
+    return intStaticTable[u];
+  }
+
+  static bool hasInt(int32_t i) { return uint32_t(i) < INT_STATIC_LIMIT; }
+
+  JSAtom* getInt(int32_t i) {
+    MOZ_ASSERT(hasInt(i));
+    return getUint(uint32_t(i));
+  }
+
+  static bool hasUnit(char16_t c) { return c < UNIT_STATIC_LIMIT; }
+
+  JSAtom* getUnit(char16_t c) {
+    MOZ_ASSERT(hasUnit(c));
+    return unitStaticTable[c];
+  }
+
+  /* May not return atom, returns null on (reported) failure. */
+  inline JSLinearString* getUnitString(JSContext* cx, char16_t c);
+
+  /* May not return atom, returns null on (reported) failure. */
+  inline JSLinearString* getUnitStringForElement(JSContext* cx, JSString* str,
+                                                 size_t index);
+
+  /* May not return atom, returns null on (reported) failure. */
+  inline JSLinearString* getUnitStringForElement(JSContext* cx,
+                                                 JSLinearString* str,
+                                                 size_t index);
+
+  template <typename CharT>
+  static bool isStatic(const CharT* chars, size_t len);
+
+  /* Return null if no static atom exists for the given (chars, length). */
+  template <typename CharT>
+  MOZ_ALWAYS_INLINE JSAtom* lookup(const CharT* chars, size_t length) {
+    static_assert(std::is_same_v<CharT, JS::Latin1Char> ||
+                      std::is_same_v<CharT, char16_t>,
+                  "for understandability, |chars| must be one of a few "
+                  "identified types");
+
+    switch (length) {
+      case 1: {
+        char16_t c = chars[0];
+        if (c < UNIT_STATIC_LIMIT) {
+          return getUnit(c);
+        }
+        return nullptr;
+      }
+      case 2:
+        if (fitsInSmallChar(chars[0]) && fitsInSmallChar(chars[1])) {
+          return getLength2(chars[0], chars[1]);
+        }
+        return nullptr;
+      case 3:
+        /*
+         * Here we know that JSString::intStringTable covers only 256 (or at
+         * least not 1000 or more) chars. We rely on order here to resolve the
+         * unit vs. int string/length-2 string atom identity issue by giving
+         * priority to unit strings for "0" through "9" and length-2 strings for
+         * "10" through "99".
+         */
+        int i;
+        if (fitsInLength3Static(chars[0], chars[1], chars[2], &i)) {
+          return getInt(i);
+        }
+        return nullptr;
+    }
+
+    return nullptr;
+  }
+
+  MOZ_ALWAYS_INLINE JSAtom* lookup(const char* chars, size_t length) {
+    // Collapse calls for |const char*| into |const Latin1Char char*| to avoid
+    // excess instantiations.
+    return lookup(reinterpret_cast<const JS::Latin1Char*>(chars), length);
+  }
+
+ private:
+  using SmallChar = uint8_t;
+
+  struct SmallCharTable {
+    SmallChar storage[SMALL_CHAR_TABLE_SIZE];
+
+    constexpr SmallChar& operator[](size_t idx) { return storage[idx]; }
+    constexpr const SmallChar& operator[](size_t idx) const {
+      return storage[idx];
+    }
+  };
+
+  static const SmallChar INVALID_SMALL_CHAR = -1;
+
+  static bool fitsInSmallChar(char16_t c) {
+    return c < SMALL_CHAR_TABLE_SIZE &&
+           toSmallCharTable[c] != INVALID_SMALL_CHAR;
+  }
+
+  template <typename CharT>
+  static bool fitsInLength3Static(CharT c1, CharT c2, CharT c3, int* i) {
+    static_assert(INT_STATIC_LIMIT <= 299,
+                  "static int strings assumed below to be at most "
+                  "three digits where the first digit is either 1 or 2");
+    if ('1' <= c1 && c1 < '3' && '0' <= c2 && c2 <= '9' && '0' <= c3 &&
+        c3 <= '9') {
+      *i = (c1 - '0') * 100 + (c2 - '0') * 10 + (c3 - '0');
+
+      if (unsigned(*i) < INT_STATIC_LIMIT) {
+        return true;
+      }
+    }
+    return false;
+  }
+
+  static constexpr JS::Latin1Char fromSmallChar(SmallChar c);
+
+  static constexpr SmallChar toSmallChar(uint32_t c);
+
+  static constexpr SmallCharTable createSmallCharTable();
+
+  static const SmallCharTable toSmallCharTable;
+
+  static constexpr JS::Latin1Char firstCharOfLength2(size_t s) {
+    return fromSmallChar(s >> SMALL_CHAR_BITS);
+  }
+  static constexpr JS::Latin1Char secondCharOfLength2(size_t s) {
+    return fromSmallChar(s & SMALL_CHAR_MASK);
+  }
+
+  static constexpr JS::Latin1Char firstCharOfLength3(uint32_t i) {
+    return '0' + (i / 100);
+  }
+  static constexpr JS::Latin1Char secondCharOfLength3(uint32_t i) {
+    return '0' + ((i / 10) % 10);
+  }
+  static constexpr JS::Latin1Char thirdCharOfLength3(uint32_t i) {
+    return '0' + (i % 10);
+  }
+
+  static MOZ_ALWAYS_INLINE size_t getLength2Index(char16_t c1, char16_t c2) {
+    MOZ_ASSERT(fitsInSmallChar(c1));
+    MOZ_ASSERT(fitsInSmallChar(c2));
+    return (size_t(toSmallCharTable[c1]) << SMALL_CHAR_BITS) +
+           toSmallCharTable[c2];
+  }
+
+  // Same as getLength2Index, but withtout runtime assertion,
+  // this should be used only for known static string.
+  static constexpr size_t getLength2IndexStatic(char c1, char c2) {
+    return (size_t(toSmallChar(c1)) << SMALL_CHAR_BITS) + toSmallChar(c2);
+  }
+
+  MOZ_ALWAYS_INLINE JSAtom* getLength2FromIndex(size_t index) {
+    return length2StaticTable[index];
+  }
+
+  MOZ_ALWAYS_INLINE JSAtom* getLength2(char16_t c1, char16_t c2) {
+    return getLength2FromIndex(getLength2Index(c1, c2));
+  }
+};
+
+/*
+ * Declare length-2 strings. We only store strings where both characters are
+ * alphanumeric. The lower 10 short chars are the numerals, the next 26 are
+ * the lowercase letters, and the next 26 are the uppercase letters.
+ */
+
+constexpr JS::Latin1Char StaticStrings::fromSmallChar(SmallChar c) {
+  if (c < 10) {
+    return c + '0';
+  }
+  if (c < 36) {
+    return c + 'a' - 10;
+  }
+  if (c < 62) {
+    return c + 'A' - 36;
+  }
+  if (c == 62) {
+    return '$';
+  }
+  return '_';
+}
+
+constexpr StaticStrings::SmallChar StaticStrings::toSmallChar(uint32_t c) {
+  if (mozilla::IsAsciiDigit(c)) {
+    return c - '0';
+  }
+  if (mozilla::IsAsciiLowercaseAlpha(c)) {
+    return c - 'a' + 10;
+  }
+  if (mozilla::IsAsciiUppercaseAlpha(c)) {
+    return c - 'A' + 36;
+  }
+  if (c == '$') {
+    return 62;
+  }
+  if (c == '_') {
+    return 63;
+  }
+  return StaticStrings::INVALID_SMALL_CHAR;
+}
+
+}  // namespace js
+
+#endif /* vm_StaticStrings_h */