DCE away base64ReverseLookup#26126
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juj merged 2 commits intoemscripten-core:mainfrom Feb 26, 2026
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Jan 16, 2026
| // Decodes a _known valid_ base64 string (without validation) and returns it as a new Uint8Array. | ||
| // Benchmarked to be around 5x faster compared to a simple | ||
| // "Uint8Array.from(atob(b64), c => c.charCodeAt(0))" (TODO: perhaps use this form in -Oz builds?) | ||
| #if !JS_BASE64_API |
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How does does JS_BASE64_API relate to SINGLE_FILE_BINARY_ENCODE? The PR description only talks about that later.
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Ah sorry, that was not so clear with GitHub diff.
By static reading the base64Decode() function starts
$base64Decode: (b64) => {
#if JS_BASE64_API
return Uint8Array.fromBase64(b64);
#else
i.e. the base64ReverseLookup object is never accessed if JS_BASE64_API is defined. So I updated the ifdef here to be consistent with that scenario as well.
sbc100
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Jan 16, 2026
…nabled, the base64Decode function was being emitted, and Closure was unable to DCE away the dependent base64ReverseLookup variable. So optimize this away manually to save code size.
This is an automatic change generated by tools/maint/rebaseline_tests.py. The following (3) test expectation files were updated by running the tests with `--rebaseline`: ``` codesize/test_codesize_hello_single_file.json: 5371 => 5273 [-98 bytes / -1.82%] codesize/test_minimal_runtime_code_size_hello_webgl2_wasm_singlefile.json: 15140 => 15046 [-94 bytes / -0.62%] codesize/test_minimal_runtime_code_size_random_printf_wasm.json: 10982 => 10884 [-98 bytes / -0.89%] Average change: -1.11% (-1.82% - -0.62%) ```
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When building -sSINGLE_FILE builds with -sSINGLE_FILE_BINARY_ENCODE enabled, the base64Decode function was being emitted, and Closure was unable to DCE away the dependent base64ReverseLookup variable. So optimize this away manually to save code size.
Also rename the
var iused by the algorithm to a__prefixed name, so that Closure compiler won't complain about duplicateivariables shadowing each other in different scopes.