CodePageUtils.cs source code in C# .NET

Source code for the .NET framework in C#

                        
Code:

                         / FX-1434 / FX-1434 / 1.0 / untmp / whidbey / REDBITS / ndp / fx / src / xsp / System / Web / Util / CodePageUtils.cs / 1 / CodePageUtils.cs
                        

                        
                            //------------------------------------------------------------------------------ 
// 
//     Copyright (c) Microsoft Corporation.  All rights reserved.
// 
//----------------------------------------------------------------------------- 

namespace System.Web.Util { 
    using System.Collections; 

    // 
    // Utility class to help with determining if a given code page
    // is ASCII compatible (preserves 0-127 Unicode characters as is)
    //
 
    internal static class CodePageUtils {
 
        /*      The following array of ASCII compatible code pages 
                is generated by running this code on a machine that
                has _many_ codepages installed: 

                using System;
                using System.Collections;
                using System.Text; 
                public class qq {
                    public static void Main(string[] args) { 
                        ArrayList list = new ArrayList(); 
                        byte[] bb = new byte[128]; for (int i = 0; i < 128; i++) bb[i] = (byte)i;
                        String asciiString = Encoding.ASCII.GetString(bb); 
                        for (int i = 1; i < 100000; i++) {
                            try {
                                Encoding e = Encoding.GetEncoding(i);
                                byte[] xx = e.GetBytes(asciiString); 
                                if (xx.Length == 128) {
                                    bool good = true; 
                                    for (int j = 0; j < 128; j++) { if (bb[j] != xx[j]) { good = false; break; } } 
                                    if (good) list.Add(i);
                                } 
                            }
                            catch {}
                        }
                        int n = list.Count; 
                        Console.Write("private const int[] _asciiCompatCodePages = new int[" + n + "] {\r\n    ");
                        for (int i = 0; i < n; i++) { 
                            Console.Write("{0,5}", list[i]); 
                            if (i < n-1) Console.Write(", ");
                            if (((i+1) % 10) == 0) Console.Write("\r\n    "); 
                        }
                        Console.Write("\r\n};\r\n");
                    }
                } 

        */ 
 
        private static int[] _asciiCompatCodePages = new int[79] {
              437,   708,   720,   737,   775,   850,   852,   855,   857,   858, 
              860,   861,   862,   863,   864,   865,   866,   869,   874,   932,
              936,   949,   950,  1250,  1251,  1252,  1253,  1254,  1255,  1256,
             1257,  1258,  1361, 10000, 10001, 10002, 10003, 10004, 10005, 10006,
            10007, 10008, 10010, 10017, 10029, 10079, 10081, 10082, 20000, 20001, 
            20002, 20003, 20004, 20005, 20127, 20866, 20932, 20936, 20949, 21866,
            28591, 28592, 28593, 28594, 28595, 28596, 28597, 28598, 28599, 28605, 
            38598, 50220, 50221, 50222, 50225, 50227, 51932, 51949, 65001 
        };
 
        internal /*public*/ static bool IsAsciiCompatibleCodePage(int codepage) {
            //alternatives to binary search considered
            //Hashtable: static initialization increases startup up, perf relative
            //Byte array would consume ~8K, but lookups constant 
            //with 80 entries, binary search limited to 7 indexes into array
            int lo = 0; 
            int hi = 78; 
            while(lo <= hi) {
                int i = (lo + hi) >> 1; 
                int c;
                c = _asciiCompatCodePages[i] - codepage;
                if (c == 0) return true; //i is the index of the item
                if (c < 0) { 
                    lo = i + 1;
                } 
                else { 
                    hi = i - 1;
                } 
            }
            return false;
            //lo is the index of the item immediately after
            //~lo returned in some implementations for false indicator with additional info 
        }
 
        internal const int CodePageUT8 = 65001; 
    }
 


}

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