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AK: Make static constexpr variables to avoid stack copy in Base64

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Alphabet and lookup table are created and copied to the stack on each
call. Create them and store them in static memory.
This commit is contained in:
Lenny Maiorani 2022-03-13 20:59:29 -06:00 committed by Linus Groh
parent d00b79568f
commit 8d1d4d4f09
Notes: sideshowbarker 2024-07-17 17:18:13 +09:00 
Author: https://github.com/ldm5180
Commit: https://github.com/SerenityOS/serenity/commit/8d1d4d4f09
Pull-request: https://github.com/SerenityOS/serenity/pull/13040
Reviewed-by: https://github.com/trflynn89
1 changed files with 14 additions and 19 deletions
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33
AK/Base64.cpp
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@ -13,24 +13,19 @@
namespace AK { namespace AK {
static constexpr auto make_alphabet() static constexpr Array alphabet = {
{ 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H',
Array alphabet = { 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P',
'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X',
'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f',
'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n',
'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v',
'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'w', 'x', 'y', 'z', '0', '1', '2', '3',
'o', 'p', 'q', 'r', 's', 't', 'u', 'v', '4', '5', '6', '7', '8', '9', '+', '/'
'w', 'x', 'y', 'z', '0', '1', '2', '3', };
'4', '5', '6', '7', '8', '9', '+', '/'
};
return alphabet;
}
static constexpr auto make_lookup_table() static consteval auto make_lookup_table()
{ {
constexpr auto alphabet = make_alphabet();
Array<i16, 256> table; Array<i16, 256> table;
table.fill(-1); table.fill(-1);
for (size_t i = 0; i < alphabet.size(); ++i) { for (size_t i = 0; i < alphabet.size(); ++i) {
@ -39,6 +34,8 @@ static constexpr auto make_lookup_table()
return table; return table;
} }
static constexpr auto alphabet_lookup_table = make_lookup_table();
size_t calculate_base64_decoded_length(StringView input) size_t calculate_base64_decoded_length(StringView input)
{ {
return input.length() * 3 / 4; return input.length() * 3 / 4;
@ -52,7 +49,6 @@ size_t calculate_base64_encoded_length(ReadonlyBytes input)
ErrorOr<ByteBuffer> decode_base64(StringView input) ErrorOr<ByteBuffer> decode_base64(StringView input)
{ {
auto get = [&](size_t& offset, bool* is_padding, bool& parsed_something) -> ErrorOr<u8> { auto get = [&](size_t& offset, bool* is_padding, bool& parsed_something) -> ErrorOr<u8> {
constexpr auto table = make_lookup_table();
while (offset < input.length() && is_ascii_space(input[offset])) while (offset < input.length() && is_ascii_space(input[offset]))
++offset; ++offset;
if (offset >= input.length()) if (offset >= input.length())
@ -65,7 +61,7 @@ ErrorOr<ByteBuffer> decode_base64(StringView input)
*is_padding = true; *is_padding = true;
return 0; return 0;
} }
i16 result = table[ch]; i16 result = alphabet_lookup_table[ch];
if (result < 0) if (result < 0)
return Error::from_string_literal("Invalid character in base64 data"); return Error::from_string_literal("Invalid character in base64 data");
VERIFY(result < 256); VERIFY(result < 256);
@ -106,7 +102,6 @@ ErrorOr<ByteBuffer> decode_base64(StringView input)
String encode_base64(ReadonlyBytes input) String encode_base64(ReadonlyBytes input)
{ {
constexpr auto alphabet = make_alphabet();
StringBuilder output(calculate_base64_encoded_length(input)); StringBuilder output(calculate_base64_encoded_length(input));
auto get = [&](const size_t offset, bool* need_padding = nullptr) -> u8 { auto get = [&](const size_t offset, bool* need_padding = nullptr) -> u8 {