135 lines
3.5 KiB
JavaScript
135 lines
3.5 KiB
JavaScript
"use strict";
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// Table with utf8 lengths (calculated by first byte of sequence)
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// Note, that 5 & 6-byte values and some 4-byte values can not be represented in JS,
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// because max possible codepoint is 0x10ffff
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var _utf8len = new Array(256);
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for (var i = 0; i < 256; i++) {
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_utf8len[i] = i >= 252 ? 6 : i >= 248 ? 5 : i >= 240 ? 4 : i >= 224 ? 3 : i >= 192 ? 2 : 1;
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}
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_utf8len[254] = _utf8len[254] = 1; // Invalid sequence start
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// eslint-disable-next-line complexity
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function buf2string(buf) {
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var i, out, c, cLen;
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var len = buf.length;
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// Reserve max possible length (2 words per char)
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// NB: by unknown reasons, Array is significantly faster for
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// String.fromCharCode.apply than Uint16Array.
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var utf16buf = new Array(len * 2);
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for (out = 0, i = 0; i < len;) {
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c = buf[i++];
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// quick process ascii
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if (c < 0x80) {
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utf16buf[out++] = c;
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continue;
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}
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cLen = _utf8len[c];
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// skip 5 & 6 byte codes
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if (cLen > 4) {
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utf16buf[out++] = 0xfffd;
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i += cLen - 1;
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continue;
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}
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// apply mask on first byte
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c &= cLen === 2 ? 0x1f : cLen === 3 ? 0x0f : 0x07;
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// join the rest
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while (cLen > 1 && i < len) {
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c = c << 6 | buf[i++] & 0x3f;
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cLen--;
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}
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// terminated by end of string?
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if (cLen > 1) {
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utf16buf[out++] = 0xfffd;
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continue;
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}
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if (c < 0x10000) {
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utf16buf[out++] = c;
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} else {
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c -= 0x10000;
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utf16buf[out++] = 0xd800 | c >> 10 & 0x3ff;
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utf16buf[out++] = 0xdc00 | c & 0x3ff;
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}
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}
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// shrinkBuf(utf16buf, out)
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if (utf16buf.length !== out) {
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if (utf16buf.subarray) {
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utf16buf = utf16buf.subarray(0, out);
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} else {
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utf16buf.length = out;
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}
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}
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// return String.fromCharCode.apply(null, utf16buf);
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return applyFromCharCode(utf16buf);
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}
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// eslint-disable-next-line complexity
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function applyFromCharCode(array) {
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// Performances notes :
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// --------------------
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// String.fromCharCode.apply(null, array) is the fastest, see
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// see http://jsperf.com/converting-a-uint8array-to-a-string/2
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// but the stack is limited (and we can get huge arrays !).
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//
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// result += String.fromCharCode(array[i]); generate too many strings !
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//
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// This code is inspired by http://jsperf.com/arraybuffer-to-string-apply-performance/2
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var chunk = 65536;
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var result = [],
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len = array.length;
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var k = 0;
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String.fromCharCode.apply(null, new Uint8Array(0));
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while (k < len && chunk > 1) {
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try {
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result.push(String.fromCharCode.apply(null, array.slice(k, Math.min(k + chunk, len))));
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k += chunk;
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} catch (e) {
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chunk = Math.floor(chunk / 2);
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}
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}
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return result.join("");
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}
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function utf8border(buf, max) {
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var pos;
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max = max || buf.length;
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if (max > buf.length) {
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max = buf.length;
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}
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// go back from last position, until start of sequence found
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pos = max - 1;
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while (pos >= 0 && (buf[pos] & 0xc0) === 0x80) {
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pos--;
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}
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// Fuckup - very small and broken sequence,
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// return max, because we should return something anyway.
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if (pos < 0) {
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return max;
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}
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// If we came to start of buffer - that means vuffer is too small,
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// return max too.
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if (pos === 0) {
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return max;
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}
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return pos + _utf8len[buf[pos]] > max ? pos : max;
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}
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function utf8decode(buf) {
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var result = [],
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len = buf.length,
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chunk = 65536;
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var k = 0;
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while (k < len) {
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var nextBoundary = utf8border(buf, Math.min(k + chunk, len));
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result.push(buf2string(buf.subarray(k, nextBoundary)));
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k = nextBoundary;
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}
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return result.join("");
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}
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module.exports = utf8decode; |