HashHelpers.cs source code in C# .NET

Source code for the .NET framework in C#

                        
Code:

                         / 4.0 / 4.0 / untmp / DEVDIV_TFS / Dev10 / Releases / RTMRel / ndp / fx / src / Core / System / Collections / Generic / HashHelpers.cs / 1305376 / HashHelpers.cs
                        

                        
                            using System; 
using System.Collections;
using System.Collections.Generic;
using System.Diagnostics;
using System.Runtime.ConstrainedExecution; 
using System.Text;
 
namespace System.Collections.Generic { 

    ///  
    /// Duplicated because internal to mscorlib
    /// 
    internal static class HashHelpers {
        // Table of prime numbers to use as hash table sizes. 
        // The entry used for capacity is the smallest prime number in this array
        // that is larger than twice the previous capacity. 
 
        internal static readonly int[] primes = {
            3, 7, 11, 17, 23, 29, 37, 47, 59, 71, 89, 107, 131, 163, 197, 239, 293, 353, 431, 521, 631, 761, 919, 
            1103, 1327, 1597, 1931, 2333, 2801, 3371, 4049, 4861, 5839, 7013, 8419, 10103, 12143, 14591,
            17519, 21023, 25229, 30293, 36353, 43627, 52361, 62851, 75431, 90523, 108631, 130363, 156437,
            187751, 225307, 270371, 324449, 389357, 467237, 560689, 672827, 807403, 968897, 1162687, 1395263,
            1674319, 2009191, 2411033, 2893249, 3471899, 4166287, 4999559, 5999471, 7199369}; 

        [ReliabilityContract(Consistency.WillNotCorruptState, Cer.Success)] 
        internal static bool IsPrime(int candidate) { 
            if ((candidate & 1) != 0) {
                int limit = (int)Math.Sqrt(candidate); 
                for (int divisor = 3; divisor <= limit; divisor += 2) {
                    if ((candidate % divisor) == 0) {
                        return false;
                    } 
                }
                return true; 
            } 
            return (candidate == 2);
        } 

        [ReliabilityContract(Consistency.WillNotCorruptState, Cer.Success)]
        internal static int GetPrime(int min) {
            Debug.Assert(min >= 0, "min less than zero; handle overflow checking before calling HashHelpers"); 

            for (int i = 0; i < primes.Length; i++) { 
                int prime = primes[i]; 
                if (prime >= min) {
                    return prime; 
                }
            }

            // Outside of our predefined table. Compute the hard way. 
            for (int i = (min | 1); i < Int32.MaxValue; i += 2) {
                if (IsPrime(i)) { 
                    return i; 
                }
            } 
            return min;
        }

        internal static int GetMinPrime() { 
            return primes[0];
        } 
    } 

} 

// File provided for Reference Use Only by Microsoft Corporation (c) 2007.
// Copyright (c) Microsoft Corporation. All rights reserved.

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