FixedStringLookup.cs source code in C# .NET

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                         / DotNET / DotNET / 8.0 / untmp / whidbey / REDBITS / ndp / fx / src / CompMod / System / Collections / Specialized / FixedStringLookup.cs / 1 / FixedStringLookup.cs
                        

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

namespace System.Collections.Specialized { 
 
    using System;
    using System.Collections; 
    using System.Diagnostics;
    using System.Globalization;

    // This class provides a very efficient way to lookup an entry in a list of strings, 
    // providing that they are declared in a particular way.
 
    // It requires the set of strings to be orderded into an array of arrays of strings. 
    // The first indexer must the length of the string, so that each sub-array is of the
    // same length. The contained array must be in alphabetical order. Furthermore, if the 
    // table is to be searched case-insensitively, the strings must all be lower case.
    internal static class FixedStringLookup {

        // Returns whether the match is found in the lookup table 
        internal static bool Contains(string[][] lookupTable, string value, bool ignoreCase) {
            int length = value.Length; 
            if (length <= 0 || length - 1 >= lookupTable.Length) { 
                return false;
            } 

            string[] subArray = lookupTable[length - 1];
            if (subArray == null) {
                return false; 
            }
            return Contains(subArray, value, ignoreCase); 
        } 

#if DEBUG 

        internal static void VerifyLookupTable(string[][] lookupTable, bool ignoreCase) {
            for (int i = 0; i < lookupTable.Length; i++) {
                string[] subArray = lookupTable[i]; 
                if (subArray != null) {
                    string lastValue = null; 
                    for (int j = 0; j < subArray.Length; j++) { 
                        string value = subArray[j];
                        // Must all be the length of the hashed position 
                        Debug.Assert(value.Length == i + 1, "Lookup table contains an item in the wrong subtable.  Item name: " + value);
                        if (lastValue != null) {
                            // Must be sorted within the sub array;
                            Debug.Assert(string.Compare(lastValue, value, ((ignoreCase) ? StringComparison.OrdinalIgnoreCase : StringComparison.Ordinal)) < 0, 
                                         String.Format(CultureInfo.InvariantCulture, "Lookup table is out of order.  Items {0} and {1} are reversed", lastValue, value));
                        } 
                        lastValue = value; 
                    }
                } 
            }
        }

#endif 

        // This routine finds a hit within a single sorted array, with the assumption that the 
        // value and all the strings are of the same length. 
        private static bool Contains(string[] array, string value, bool ignoreCase) {
            int min = 0; 
            int max = array.Length;
            int pos = 0;
            char searchChar;
            while (pos < value.Length) { 
                if (ignoreCase) {
                    searchChar = char.ToLower(value[pos], CultureInfo.InvariantCulture); 
                } else { 
                    searchChar = value[pos];
                } 
                if ((max - min) <= 1) {
                    // we are down to a single item, so we can stay on this row until the end.
                    if (searchChar != array[min][pos]) {
                        return false; 
                    }
                    pos++; 
                    continue; 
                }
 
                // There are multiple items to search, use binary search to find one of the hits
                if (!FindCharacter(array, searchChar, pos, ref min, ref max)) {
                    return false;
                } 
                // and move to next char
                pos++; 
            } 
            return true;
        } 

        // Do a binary search on the character array at the specific position and constrict the ranges appropriately.
        private static bool FindCharacter(string[] array, char value, int pos, ref int min, ref int max) {
            int index = min; 
            while (min < max) {
                index = (min + max) / 2; 
                char comp = array[index][pos]; 
                if (value == comp) {
                    // We have a match. Now adjust to any adjacent matches 
                    int newMin = index;
                    while (newMin > min && array[newMin - 1][pos] == value) {
                        newMin--;
                    } 
                    min = newMin;
 
                    int newMax = index + 1; 
                    while (newMax < max && array[newMax][pos] == value) {
                        newMax++; 
                    }
                    max = newMax;
                    return true;
                } 
                if (value < comp) {
                    max = index; 
                } 
                else {
                    min = index + 1; 
                }
            }
            return false;
        } 
    }
}

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