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src: use stack allocation for small string encoding#62431

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thisalihassan wants to merge 2 commits intonodejs:mainfrom
thisalihassan:src-string-bytes-stack-encode
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src: use stack allocation for small string encoding#62431
thisalihassan wants to merge 2 commits intonodejs:mainfrom
thisalihassan:src-string-bytes-stack-encode

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@thisalihassan thisalihassan commented Mar 25, 2026

  • Introduce EncodeOneByteString / EncodeTwoByteString helper templates in StringBytes::Encode() that use a 512 byte (256-char for two-byte) stack buffer for small inputs, falling back to heap allocation + ExternString for larger ones.
  • Covers all encoding paths: ASCII, HEX, BASE64, BASE64URL, UTF8 (two-byte), and UCS2.

Refs: nodejs/performance#194

                                                                       confidence improvement accuracy (*)   (**)  (***)
buffers/buffer-base64-encode.js n=32 len=67108864                                      1.82 %       ±2.53% ±3.38% ±4.42%
buffers/buffer-base64url-encode.js n=32 len=67108864                            *     -1.70 %       ±1.39% ±1.86% ±2.42%
buffers/buffer-tostring.js n=1000000 len=1 args=0 encoding=''                 ***      3.71 %       ±1.67% ±2.23% ±2.91%
buffers/buffer-tostring.js n=1000000 len=1 args=1 encoding='ascii'                     0.21 %       ±2.08% ±2.78% ±3.65%
buffers/buffer-tostring.js n=1000000 len=1 args=1 encoding='hex'              ***     40.34 %       ±4.17% ±5.60% ±7.39%
buffers/buffer-tostring.js n=1000000 len=1 args=1 encoding='latin1'           ***      2.52 %       ±1.15% ±1.53% ±1.99%
buffers/buffer-tostring.js n=1000000 len=1 args=1 encoding='UCS-2'            ***      3.33 %       ±1.26% ±1.68% ±2.19%
buffers/buffer-tostring.js n=1000000 len=1 args=1 encoding='utf8'             ***      2.03 %       ±0.90% ±1.19% ±1.55%
buffers/buffer-tostring.js n=1000000 len=1 args=3 encoding='ascii'              *      3.00 %       ±2.83% ±3.80% ±5.02%
buffers/buffer-tostring.js n=1000000 len=1 args=3 encoding='hex'              ***     40.40 %       ±3.23% ±4.30% ±5.59%
buffers/buffer-tostring.js n=1000000 len=1 args=3 encoding='latin1'            **      2.93 %       ±2.04% ±2.73% ±3.58%
buffers/buffer-tostring.js n=1000000 len=1 args=3 encoding='UCS-2'            ***      4.55 %       ±1.17% ±1.56% ±2.04%
buffers/buffer-tostring.js n=1000000 len=1 args=3 encoding='utf8'             ***      2.52 %       ±0.88% ±1.17% ±1.52%
buffers/buffer-tostring.js n=1000000 len=1024 args=0 encoding=''                      -0.48 %       ±1.75% ±2.35% ±3.09%
buffers/buffer-tostring.js n=1000000 len=1024 args=1 encoding='ascii'                  2.68 %       ±3.68% ±4.91% ±6.44%
buffers/buffer-tostring.js n=1000000 len=1024 args=1 encoding='hex'                   -0.05 %       ±1.47% ±1.96% ±2.55%
buffers/buffer-tostring.js n=1000000 len=1024 args=1 encoding='latin1'          *      2.53 %       ±1.94% ±2.60% ±3.41%
buffers/buffer-tostring.js n=1000000 len=1024 args=1 encoding='UCS-2'                  0.75 %       ±1.80% ±2.40% ±3.13%
buffers/buffer-tostring.js n=1000000 len=1024 args=1 encoding='utf8'            *      3.19 %       ±2.47% ±3.33% ±4.40%
buffers/buffer-tostring.js n=1000000 len=1024 args=3 encoding='ascii'                  0.01 %       ±2.15% ±2.86% ±3.72%
buffers/buffer-tostring.js n=1000000 len=1024 args=3 encoding='hex'                    0.40 %       ±1.31% ±1.74% ±2.26%
buffers/buffer-tostring.js n=1000000 len=1024 args=3 encoding='latin1'          *      1.96 %       ±1.86% ±2.48% ±3.23%
buffers/buffer-tostring.js n=1000000 len=1024 args=3 encoding='UCS-2'                  0.54 %       ±1.99% ±2.65% ±3.46%
buffers/buffer-tostring.js n=1000000 len=1024 args=3 encoding='utf8'                   1.05 %       ±1.11% ±1.48% ±1.93%
buffers/buffer-tostring.js n=1000000 len=64 args=0 encoding=''                        -0.37 %       ±1.28% ±1.72% ±2.26%
buffers/buffer-tostring.js n=1000000 len=64 args=1 encoding='ascii'                   -1.33 %       ±2.21% ±2.97% ±3.92%
buffers/buffer-tostring.js n=1000000 len=64 args=1 encoding='hex'             ***     41.64 %       ±2.07% ±2.76% ±3.62%
buffers/buffer-tostring.js n=1000000 len=64 args=1 encoding='latin1'            *      1.98 %       ±1.86% ±2.48% ±3.25%
buffers/buffer-tostring.js n=1000000 len=64 args=1 encoding='UCS-2'                   -0.38 %       ±2.76% ±3.68% ±4.80%
buffers/buffer-tostring.js n=1000000 len=64 args=1 encoding='utf8'                     0.64 %       ±0.88% ±1.18% ±1.53%
buffers/buffer-tostring.js n=1000000 len=64 args=3 encoding='ascii'                    0.35 %       ±2.91% ±3.88% ±5.07%
buffers/buffer-tostring.js n=1000000 len=64 args=3 encoding='hex'             ***     40.54 %       ±1.43% ±1.90% ±2.48%
buffers/buffer-tostring.js n=1000000 len=64 args=3 encoding='latin1'                   1.67 %       ±2.47% ±3.30% ±4.31%
buffers/buffer-tostring.js n=1000000 len=64 args=3 encoding='UCS-2'                    0.32 %       ±1.93% ±2.57% ±3.35%
buffers/buffer-tostring.js n=1000000 len=64 args=3 encoding='utf8'                     0.56 %       ±0.91% ±1.21% ±1.58%

Be aware that when doing many comparisons the risk of a false-positive
result increases. In this case, there are 35 comparisons, you can thus
expect the following amount of false-positive results:
  1.75 false positives, when considering a   5% risk acceptance (*, **, ***),
  0.35 false positives, when considering a   1% risk acceptance (**, ***),
  0.04 false positives, when considering a 0.1% risk acceptance (***)
thisalihassan@Alis-MacBook-Pro node %

@nodejs-github-bot nodejs-github-bot added buffer Issues and PRs related to the buffer subsystem. c++ Issues and PRs that require attention from people who are familiar with C++. needs-ci PRs that need a full CI run. labels Mar 25, 2026
@thisalihassan thisalihassan force-pushed the src-string-bytes-stack-encode branch from e5fbafb to 43fd2f8 Compare March 25, 2026 11:05
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codecov bot commented Mar 25, 2026 •
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Codecov Report

❌ Patch coverage is 87.50000% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 89.80%. Comparing base (f48ac91) to head (f38c303).
⚠️ Report is 14 commits behind head on main.

Files with missing lines Patch % Lines
src/string_bytes.cc 87.50% 0 Missing and 6 partials ⚠️
Additional details and impacted files 
@@            Coverage Diff             @@
##             main   #62431      +/-   ##
==========================================
+ Coverage   89.77%   89.80%   +0.02%     
==========================================
  Files         697      697              
  Lines      215749   215755       +6     
  Branches    41304    41285      -19     
==========================================
+ Hits       193681   193751      +70     
+ Misses      14161    14123      -38     
+ Partials     7907     7881      -26
Files with missing lines Coverage Δ
src/string_bytes.cc 74.63% <87.50%> (+4.96%) ⬆️

... and 52 files with indirect coverage changes

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  • ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
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Flarna
Flarna reviewed Mar 26, 2026
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@thisalihassan thisalihassan force-pushed the src-string-bytes-stack-encode branch from 43fd2f8 to 73eb342 Compare March 27, 2026 12:26
ronag
ronag reviewed Mar 29, 2026
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ronag
ronag reviewed Mar 29, 2026
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src/string_bytes.cc Outdated
Comment on lines +553 to +560
case BUFFER: {
auto maybe_buf = Buffer::Copy(isolate, buf, buflen);
Local<v8::Object> buf;
if (!maybe_buf.ToLocal(&buf)) {
isolate->ThrowException(node::ERR_MEMORY_ALLOCATION_FAILED(isolate));
}
return buf;
}
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@ronag ronag Mar 29, 2026

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Seems like unnecessary whitespace change?

ronag
ronag reviewed Mar 29, 2026
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@ronag ronag added the author ready PRs that have at least one approval, no pending requests for changes, and a CI started. label Mar 29, 2026
@ronag ronag added the request-ci Add this label to start a Jenkins CI on a PR. label Mar 29, 2026
@github-actions github-actions bot removed the request-ci Add this label to start a Jenkins CI on a PR. label Mar 29, 2026
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nodejs-github-bot commented Mar 29, 2026

CI: https://ci.nodejs.org/job/node-test-pull-request/72188/

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thisalihassan commented Mar 30, 2026

Falky tests are failing:

  1. parallel.test-debugger-heap-profiler
  2. sequential.test-watch-mode-restart-esm-loading-error
  3. parallel.test-debugger-heap-profiler
  4. es-module.test-vm-contextified-script-leak
  5. sequential.test-watch-mode-restart-esm-loading-error
  6. es-module.test-vm-contextified-script-leak

@ronag ronag added the request-ci Add this label to start a Jenkins CI on a PR. label Mar 31, 2026
@github-actions github-actions bot removed the request-ci Add this label to start a Jenkins CI on a PR. label Mar 31, 2026
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nodejs-github-bot commented Apr 6, 2026

CI: https://ci.nodejs.org/job/node-test-pull-request/72519/

@thisalihassan
src: use stack allocation for small string encoding
d6bbc57 
Use stack-allocated buffers in StringBytes::Encode() for small inputs
instead of heap-allocating via UncheckedMalloc for every call.

Refs: nodejs/performance#194
@thisalihassan
remove unnecessary whitespace change
f38c303
@thisalihassan thisalihassan force-pushed the src-string-bytes-stack-encode branch from fd449b1 to f38c303 Compare April 7, 2026 11:08
@Flarna Flarna added the request-ci Add this label to start a Jenkins CI on a PR. label Apr 8, 2026
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thisalihassan commented Apr 8, 2026 •
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@Flarna for somereason CI is not getting triggered even after you added the label, is there a delay?
NVM it started after ~40min :')

@github-actions github-actions bot removed the request-ci Add this label to start a Jenkins CI on a PR. label Apr 8, 2026
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CI: https://ci.nodejs.org/job/node-test-pull-request/72564/

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