lib/utf8/index.js

"use strict";

/**
 * A minimal UTF8 implementation for number arrays.
 * @memberof util
 * @namespace
 */
var utf8 = exports;

/**
 * Calculates the UTF8 byte length of a string.
 * @param {string} string String
 * @returns {number} Byte length
 */
utf8.length = function utf8_length(string) {
    var len = 0,
        c = 0;
    for (var i = 0; i < string.length; ++i) {
        c = string.charCodeAt(i);
        if (c < 128)
            len += 1;
        else if (c < 2048)
            len += 2;
        else if ((c & 0xFC00) === 0xD800 && (string.charCodeAt(i + 1) & 0xFC00) === 0xDC00) {
            ++i;
            len += 4;
        } else
            len += 3;
    }
    return len;
};

/**
 * Reads UTF8 bytes as a string.
 * @param {Uint8Array} buffer Source buffer
 * @param {number} start Source start
 * @param {number} end Source end
 * @returns {string} String read
 */
utf8.read = function utf8_read(buffer, start, end) {
    if (end - start < 1) {
        return "";
    }

    var str = "";
    for (var i = start; i < end;) {
        var t = buffer[i++];
        if (t <= 0x7F) {
            str += String.fromCharCode(t);
        } else if (t >= 0xC0 && t < 0xE0) {
            str += String.fromCharCode((t & 0x1F) << 6 | buffer[i++] & 0x3F);
        } else if (t >= 0xE0 && t < 0xF0) {
            str += String.fromCharCode((t & 0xF) << 12 | (buffer[i++] & 0x3F) << 6 | buffer[i++] & 0x3F);
        } else if (t >= 0xF0) {
            var t2 = ((t & 7) << 18 | (buffer[i++] & 0x3F) << 12 | (buffer[i++] & 0x3F) << 6 | buffer[i++] & 0x3F) - 0x10000;
            str += String.fromCharCode(0xD800 + (t2 >> 10));
            str += String.fromCharCode(0xDC00 + (t2 & 0x3FF));
        }
    }

    return str;
};

/**
 * Writes a string as UTF8 bytes.
 * @param {string} string Source string
 * @param {Uint8Array} buffer Destination buffer
 * @param {number} offset Destination offset
 * @returns {number} Bytes written
 */
utf8.write = function utf8_write(string, buffer, offset) {
    var start = offset,
        c1, // character 1
        c2; // character 2
    for (var i = 0; i < string.length; ++i) {
        c1 = string.charCodeAt(i);
        if (c1 < 128) {
            buffer[offset++] = c1;
        } else if (c1 < 2048) {
            buffer[offset++] = c1 >> 6       | 192;
            buffer[offset++] = c1       & 63 | 128;
        } else if ((c1 & 0xFC00) === 0xD800 && ((c2 = string.charCodeAt(i + 1)) & 0xFC00) === 0xDC00) {
            c1 = 0x10000 + ((c1 & 0x03FF) << 10) + (c2 & 0x03FF);
            ++i;
            buffer[offset++] = c1 >> 18      | 240;
            buffer[offset++] = c1 >> 12 & 63 | 128;
            buffer[offset++] = c1 >> 6  & 63 | 128;
            buffer[offset++] = c1       & 63 | 128;
        } else {
            buffer[offset++] = c1 >> 12      | 224;
            buffer[offset++] = c1 >> 6  & 63 | 128;
            buffer[offset++] = c1       & 63 | 128;
        }
    }
    return offset - start;
};