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Simplify + optimize lengthBytesUTF8. Don't fully decode surrogates #17413

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Merged
merged 5 commits into from
Jul 17, 2022
Merged

Simplify + optimize lengthBytesUTF8. Don't fully decode surrogates #17413

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e31b77f
Simplify + optimize lengthBytesUTF8. Don't fully decode surrogates
MaxGraey Jul 12, 2022
bd6ba15
fix len
MaxGraey Jul 15, 2022
3fc3812
revert cached str.length
MaxGraey Jul 15, 2022
ebf6e0c
let -> var
MaxGraey Jul 15, 2022
55bd221
trigger ci
MaxGraey Jul 15, 2022
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16 changes: 10 additions & 6 deletions src/runtime_strings.js
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Original file line number Diff line number Diff line change
Expand Up @@ -191,12 +191,16 @@ function lengthBytesUTF8(str) {
for (var i = 0; i < str.length; ++i) {
// Gotcha: charCodeAt returns a 16-bit word that is a UTF-16 encoded code unit, not a Unicode code point of the character! So decode UTF16->UTF32->UTF8.
// See http://unicode.org/faq/utf_bom.html#utf16-3
var u = str.charCodeAt(i); // possibly a lead surrogate
if (u >= 0xD800 && u <= 0xDFFF) u = 0x10000 + ((u & 0x3FF) << 10) | (str.charCodeAt(++i) & 0x3FF);
if (u <= 0x7F) ++len;
else if (u <= 0x7FF) len += 2;
else if (u <= 0xFFFF) len += 3;
else len += 4;
var c = str.charCodeAt(i); // possibly a lead surrogate
if (c <= 0x7F) {
len++;
} else if (c <= 0x7FF) {
len += 2;
} else if (c >= 0xD800 && c <= 0xDFFF) {
len += 4; ++i;
} else {
len += 3;
}
}
return len;
}