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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
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;
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 */