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Merged
nodejs-github-bot merged 12 commits into from
Sep 19, 2024
Merged

tools: refactor js2c.cc to use c++20 #54849

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de21f61
tools: refactor js2c.cc to use c++20
anonrig Sep 8, 2024
af4aeac
reducing memory usage and making GetCode's buffer potentially evaluat…
lemire Sep 8, 2024
143b3b4
Update js2c.cc
anonrig Sep 8, 2024
c302c78
Update js2c.cc
anonrig Sep 8, 2024
48ca54d
lint
lemire Sep 8, 2024
8d7a19f
minor fix
lemire Sep 9, 2024
15a0abc
Update tools/js2c.cc
anonrig Sep 9, 2024
caacead
removing constexpr
lemire Sep 9, 2024
93aed49
lint
lemire Sep 9, 2024
f39b3dc
Update tools/js2c.cc
anonrig Sep 11, 2024
fc7b2ef
Update tools/js2c.cc
anonrig Sep 11, 2024
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Update tools/js2c.cc
anonrig Sep 11, 2024
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reducing memory usage and making GetCode's buffer potentially evaluat… 
…ed at compile time
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@lemire @anonrig
lemire authored and anonrig committed Sep 8, 2024
commit af4aeac64dbf0625333885ae7afae8968885a62c
42 changes: 35 additions & 7 deletions tools/js2c.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -359,17 +359,45 @@ std::string GetVariableName(const std::string& id) {
return result;
}

static const std::array<std::string, 65536> GetCodeTable() {
std::array<std::string, 65536> table{};
for (size_t i = 0; i < 65536; ++i) {
table[i] = std::to_string(i) + ',';


constexpr std::pair<std::array<char, 382106>,std::array<uint32_t, 65537>> precompute_string() {
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std::array<char, 382106> str;
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std::array<uint32_t, 65537> off;
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off[0] = 0;
char *p = &str[0];
// We roll our own int to string conversion to get constexpr
constexpr auto const_int_to_str = [](uint16_t value, char *s) -> size_t {
int index = 0;
do {
s[index++] = '0' + (value % 10);
value /= 10;
} while (value != 0);

for (int i = 0; i < index / 2; ++i) {
char temp = s[i];
s[i] = s[index - i - 1];
s[index - i - 1] = temp;
}
s[index] = ',';
return index;
};
for (int i = 0; i < 65536; ++i) {
size_t offset = const_int_to_str(i, p);
p += offset;
off[i + 1] = off[i] + offset;
}
return table;
return {str, off};
}

const std::string_view GetCode(uint16_t index) {
static std::array<std::string, 65536> table = GetCodeTable();
return table[index];
// uses about 644254 bytes of memory. An array of 65536 strings might use
// 2097152 bytes so we save 3x the memory
// Furthermore, compilers such as GCC will evaluate precompute_string() at compile time, thus
// potentially speeding up the program's startup time.
static auto [backing_string, offsets] = precompute_string();
return std::string_view(&backing_string[offsets[index]],
offsets[index + 1] - offsets[index]);
}

#ifdef NODE_JS2C_USE_STRING_LITERALS
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