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AK: Avoid StringBuilder when creating a Base64-encoded string

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We don't really need the features provided by StringBuilder here, since
we know the exact size of the output. Avoiding StringBuilder avoids the
recurring capacity/size checks both within StringBuilder itself and its
internal ByteBuffer.

This reduces the runtime of `./bin/base64 enwik8 >/dev/null` from
0.976s to 0.428s.

(enwik8 is a 100MB test file from http://mattmahoney.net/dc/enwik8.zip)
This commit is contained in:
Timothy Flynn 2024-03-20 11:18:27 -04:00 • committed by Andreas Kling
parent 5f5b8ee9bb
commit 0fd7ad09a0
Notes: sideshowbarker 2024-07-17 08:43:11 +09:00
1 changed files with 7 additions and 11 deletions
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18
AK/Base64.cpp
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@ -82,7 +82,8 @@ ErrorOr<ByteBuffer> decode_base64_impl(StringView input)
template<auto alphabet>
ErrorOr<String> encode_base64_impl(ReadonlyBytes input)
{
StringBuilder output(calculate_base64_encoded_length(input));
Vector<u8> output;
TRY(output.try_ensure_capacity(calculate_base64_encoded_length(input)));
auto get = [&](const size_t offset, bool* need_padding = nullptr) -> u8 {
if (offset >= input.size()) {
@ -106,18 +107,13 @@ ErrorOr<String> encode_base64_impl(ReadonlyBytes input)
const u8 index2 = ((in1 << 2) | (in2 >> 6)) & 0x3f;
const u8 index3 = in2 & 0x3f;
char const out0 = alphabet[index0];
char const out1 = alphabet[index1];
char const out2 = is_16bit ? '=' : alphabet[index2];
char const out3 = is_8bit ? '=' : alphabet[index3];
TRY(output.try_append(out0));
TRY(output.try_append(out1));
TRY(output.try_append(out2));
TRY(output.try_append(out3));
output.unchecked_append(alphabet[index0]);
output.unchecked_append(alphabet[index1]);
output.unchecked_append(is_16bit ? '=' : alphabet[index2]);
output.unchecked_append(is_8bit ? '=' : alphabet[index3]);
}
return output.to_string_without_validation();
return String::from_utf8_without_validation(output);
}
ErrorOr<ByteBuffer> decode_base64(StringView input)