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Introducing late Uint8Array initialization #275

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Introducing late Uint8Array initialization #275

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9af4221
Introducing late Uint8Array initialization
SergeyRusskih Mar 31, 2023
4867557
Adding missing if statement
SergeyRusskih Mar 31, 2023
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17 changes: 12 additions & 5 deletions lib/utils/strings.js
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Original file line number Diff line number Diff line change
Expand Up @@ -15,12 +15,16 @@ try { String.fromCharCode.apply(null, new Uint8Array(1)); } catch (__) { STR_APP
// Table with utf8 lengths (calculated by first byte of sequence)
// Note, that 5 & 6-byte values and some 4-byte values can not be represented in JS,
// because max possible codepoint is 0x10ffff
const _utf8len = new Uint8Array(256);
for (let q = 0; q < 256; q++) {
_utf8len[q] = (q >= 252 ? 6 : q >= 248 ? 5 : q >= 240 ? 4 : q >= 224 ? 3 : q >= 192 ? 2 : 1);
let _utf8len = null;
function maybeInitializeUtf8LenBuffer() {
if (_utf8len === null) {
_utf8len = new Uint8Array(256);
for (let q = 0; q < 256; q++) {
_utf8len[q] = (q >= 252 ? 6 : q >= 248 ? 5 : q >= 240 ? 4 : q >= 224 ? 3 : q >= 192 ? 2 : 1);
}
_utf8len[254] = _utf8len[254] = 1; // Invalid sequence start
}
}
_utf8len[254] = _utf8len[254] = 1; // Invalid sequence start


// convert string to array (typed, when possible)
module.exports.string2buf = (str) => {
Expand Down Expand Up @@ -113,6 +117,7 @@ module.exports.buf2string = (buf, max) => {
// NB: by unknown reasons, Array is significantly faster for
// String.fromCharCode.apply than Uint16Array.
const utf16buf = new Array(len * 2);
maybeInitializeUtf8LenBuffer();

for (out = 0, i = 0; i < len;) {
let c = buf[i++];
Expand Down Expand Up @@ -169,6 +174,8 @@ module.exports.utf8border = (buf, max) => {
// If we came to start of buffer - that means buffer is too small,
// return max too.
if (pos === 0) { return max; }

maybeInitializeUtf8LenBuffer();

return (pos + _utf8len[buf[pos]] > max) ? pos : max;
};