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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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