50 lines
1.9 KiB
C#
50 lines
1.9 KiB
C#
using System;
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using System.Collections.Generic;
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using System.Text;
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using CubicNoise.Noisers;
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namespace CubicNoise
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{
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/// <summary>
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/// Extension methods for this library.
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/// </summary>
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public static class Extensions
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{
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//
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/// <summary>
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/// This is a deterministic hash function for strings. The official hash methods in .NET Core are no longer
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/// deterministic due to possible hashing attacks, cf. https://youtu.be/R2Cq3CLI6H8.
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///
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/// The source for this implementation: https://andrewlock.net/why-is-string-gethashcode-different-each-time-i-run-my-program-in-net-core/.
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/// Thanks Andrew for providing such a hash function.
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///
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/// Aware: Never use this hash function for any security-related task or for any hashtable storage, etc.
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///
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/// Please use it only in the case, that you really need a deterministic value. In the context of this
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/// library, the hash values are usually used for media, games, art, or simulations in order to share
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/// results with others. This is the only valid use case!
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/// </summary>
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/// <param name="str">The string for which a hash value is to be computed.</param>
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/// <returns>A deterministic 32 bit / 4 byte hash value of the given string.</returns>
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public static int GetDeterministicHashCode(this string str)
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{
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unchecked
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{
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var hash1 = (5381 << 16) + 5381;
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var hash2 = hash1;
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for (var i = 0; i < str.Length; i += 2)
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{
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hash1 = ((hash1 << 5) + hash1) ^ str[i];
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if (i == str.Length - 1)
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break;
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hash2 = ((hash2 << 5) + hash2) ^ str[i + 1];
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}
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return hash1 + (hash2 * 1566083941);
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}
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}
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}
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}
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