UTF8ToUTF16.js

// Utf8 parse performance: 1000 * 140kb ~ 140mb
// UTF8ToUTF16: 520ms
// Buffer.toString: 510ms

// Convert utf16 to utf8 performance: 1000 * 125k length
// UTF16ToUTF8: 420ms
// Buffer.toString: 1000ms

function UTF8ToUTF16(arr) {
    var arrBuff = new ArrayBuffer(arr.length * 2);
    var out = new Uint16Array(arrBuff);
    var pos = 0;
    var c = 0;
    while (pos < arr.length) {
        var c1 = arr[pos++];
        if (c1 < 128) {
            out[c] = c1;
            c++;
        }
        else if (c1 > 191 && c1 < 224) {
            var c2 = arr[pos++];
            out[c] = (c1 & 31) << 6 | c2 & 63;
            c++;
        }
        else if (c1 > 239 && c1 < 365) {
            // Surrogate Pair
            var c2 = arr[pos++];
            var c3 = arr[pos++];
            var c4 = arr[pos++];
            var u = ((c1 & 7) << 18 | (c2 & 63) << 12 | (c3 & 63) << 6 | c4 & 63) - 0x10000;
            out[c] = (0xD800 + (u >> 10));
            c++;
            out[c] = (0xDC00 + (u & 1023));
            c++;
        }
        else {
            var c2 = arr[pos++];
            var c3 = arr[pos++];
            out[c] = (c1 & 15) << 12 | (c2 & 63) << 6 | c3 & 63;
            c++;
        }
    }
    return new Uint16Array(arrBuff, 0, c);
};


function UTF16ToUTF8(arr) {
    var arrBuff = new ArrayBuffer(arr.length * 2);
    var out = new Uint8Array(arrBuff);
    var p = 0;
    for (var i = 0; i < arr.length; i++) {
        var c = arr[i];
        if (c < 128) {
            out[p++] = c;
        } else if (c < 2048) {
            out[p++] = (c >> 6) | 192;
            out[p++] = (c & 63) | 128;
        } else if (((c & 0xFC00) == 0xD800) && ((arr[i + 1] & 0xFC00) == 0xDC00)) {
            // Surrogate Pair
            c = 0x10000 + ((c & 0x03FF) << 10) + (arr[++i] & 0x03FF);
            out[p++] = (c >> 18) | 240;
            out[p++] = ((c >> 12) & 63) | 128;
            out[p++] = ((c >> 6) & 63) | 128;
            out[p++] = (c & 63) | 128;
        } else {
            out[p++] = (c >> 12) | 224;
            out[p++] = ((c >> 6) & 63) | 128;
            out[p++] = (c & 63) | 128;
        }
    }
    return new Uint8Array(arrBuff, 0, p);
};


var fs = require('fs');



// make hot
var hotBuff = new Buffer('abcdабсд𝟘𝟙𝟚𝟛𝟜𝟝𝟞𝟟𝟠𝟡”№•—', 'utf-8');
for (var i = 0; i < 500; i++) {
    var res = UTF8ToUTF16(hotBuff);
    var res2 = UTF16ToUTF8(res);
}

var buff = fs.readFileSync('./test.html');
var buffStr = buff.toString();
var utf16Buff = UTF8ToUTF16(buff);
var utf8Buff = UTF16ToUTF8(utf16Buff);
// console.log(buff.length == utf8Buff.length, buffStr.length == utf16Buff.length);


console.time('perf');
for (var i = 0; i < 1000; i++) {
    // var res = utf8ToUTF16(buff);
    // var res12 = UTF8ToUTF16(buff);
    // var res23 = buff.toString();
    // new Buffer(buffStr);
    var res10 = UTF16ToUTF8(utf16Buff);
    // new Buffer(res10.buffer);
}
console.timeEnd('perf');

// String.fromCharCode.apply(null, res);