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DCE away base64ReverseLookup #26126

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DCE away base64ReverseLookup #26126

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2 changes: 2 additions & 0 deletions src/lib/libbase64.js
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Original file line number Diff line number Diff line change
Expand Up @@ -8,6 +8,7 @@ addToLibrary({
// 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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@sbc100 sbc100 Jan 16, 2026

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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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@juj juj Jan 16, 2026

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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.

$base64Decode__postset: `
// Precreate a reverse lookup table from chars
// "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/" back to
Expand All @@ -20,6 +21,7 @@ addToLibrary({
base64ReverseLookup[43] = 62; // '+'
base64ReverseLookup[47] = 63; // '/'
`,
#endif
$base64Decode__docs: '/** @noinline */',
$base64Decode: (b64) => {
#if JS_BASE64_API
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2 changes: 1 addition & 1 deletion tools/link.py
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Expand Up @@ -1969,7 +1969,7 @@ def phase_emscript(in_wasm, wasm_target, js_syms, base_metadata):

# No need to support base64 embedding in wasm2js mode since
# the module is already in JS format.
if settings.SINGLE_FILE and not settings.WASM2JS:
if settings.SINGLE_FILE and not settings.SINGLE_FILE_BINARY_ENCODE and not settings.WASM2JS:
settings.SUPPORT_BASE64_EMBEDDING = 1
settings.DEFAULT_LIBRARY_FUNCS_TO_INCLUDE.append('$base64Decode')

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