外国的一个blog上摘录的，原文如下：

Recently I’ve been doing some work on a PHP script that has to process a bunch of XML files (in this case they’re imsmanifest files) however a few of them weren’t being parsed successfully.

The problem was soon quite clear, some of the files had been encoded using UTF-16 which wasn’t playing nicely with PHP. To solve this I’ve written a function that attempts to detect if a string is encoded using UTF-16 (little endian or big endian) and then converts it to a slightly more PHP friendly UTF-8. All the complicated stuff is copied from these JavaScript functions for converting between UTF-8 and UTF-16.


PHP:
function utf16_to_utf8($str) { $c0 = ord($str[0]); $c1 = ord($str[1]); if ($c0 == 0xFE && $c1 == 0xFF) { $be = true; } else if ($c0 == 0xFF && $c1 == 0xFE) { $be = false; } else { return $str; } $str = substr($str, 2); $len = strlen($str); $dec = ''; for ($i = 0; $i < $len; $i += 2) { $c = ($be) ? ord($str[$i]) << 8 | ord($str[$i + 1]) : ord($str[$i + 1]) << 8 | ord($str[$i]); if ($c >= 0x0001 && $c <= 0x007F) { $dec .= chr($c); } else if ($c > 0x07FF) { $dec .= chr(0xE0 | (($c >> 12) & 0x0F)); $dec .= chr(0x80 | (($c >> 6) & 0x3F)); $dec .= chr(0x80 | (($c >> 0) & 0x3F)); } else { $dec .= chr(0xC0 | (($c >> 6) & 0x1F)); $dec .= chr(0x80 | (($c >> 0) & 0x3F)); } } return $dec; }

JavaScript:
/* utf.js - UTF-8 <=> UTF-16 convertion * * Copyright (C) 1999 Masanao Izumo <iz@onicos.co.jp> * Version: 1.0 * LastModified: Dec 25 1999 * This library is free. You can redistribute it and/or modify it. */ /* * Interfaces: * utf8 = utf16to8(utf16); * utf16 = utf16to8(utf8); */ function utf16to8(str) { var out, i, len, c; out = ""; len = str.length; for(i = 0; i < len; i++) { c = str.charCodeAt(i); if ((c >= 0x0001) && (c <= 0x007F)) { out += str.charAt(i); } else if (c > 0x07FF) { out += String.fromCharCode(0xE0 | ((c >> 12) & 0x0F)); out += String.fromCharCode(0x80 | ((c >> 6) & 0x3F)); out += String.fromCharCode(0x80 | ((c >> 0) & 0x3F)); } else { out += String.fromCharCode(0xC0 | ((c >> 6) & 0x1F)); out += String.fromCharCode(0x80 | ((c >> 0) & 0x3F)); } } return out; } function utf8to16(str) { var out, i, len, c; var char2, char3; out = ""; len = str.length; i = 0; while(i < len) { c = str.charCodeAt(i++); switch(c >> 4) { case 0: case 1: case 2: case 3: case 4: case 5: case 6: case 7: // 0xxxxxxx out += str.charAt(i-1); break; case 12: case 13: // 110x xxxx 10xx xxxx char2 = str.charCodeAt(i++); out += String.fromCharCode(((c & 0x1F) << 6) | (char2 & 0x3F)); break; case 14: // 1110 xxxx 10xx xxxx 10xx xxxx char2 = str.charCodeAt(i++); char3 = str.charCodeAt(i++); out += String.fromCharCode(((c & 0x0F) << 12) | ((char2 & 0x3F) << 6) | ((char3 & 0x3F) << 0)); break; } } return out; }
原文地址：
http://www.moddular.org/log/utf16-to-utf8