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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/. */
+
+#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;
+
+ JSAtom* length2StaticTable[NUM_LENGTH2_ENTRIES] = {}; // zeroes
+
+ public:
+ /* We keep these public for the JITs. */
+ static const size_t UNIT_STATIC_LIMIT = 256U;
+ JSAtom* unitStaticTable[UNIT_STATIC_LIMIT] = {}; // zeroes
+
+ static const size_t INT_STATIC_LIMIT = 256U;
+ JSAtom* intStaticTable[INT_STATIC_LIMIT] = {}; // zeroes
+
+ 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* getUnitStringForElement(JSContext* cx, JSString* 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 */