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dotnet clr
group:Match GetHashCode between .NET 1.1 app and non-.NET app
dotnet clr:
string that matches the hash that the same string returns from the .NET 1.1 String.GetHashCode(). The .NET framework may not be on the machine, so I can't rely on it in any way. Does anyone know what the .NET 1.1 GetHashCode algorithm is?
Hello ALV,
Use Reflector to get algorithm Code below from the .net 2.0 (have no 1.1 nearby) /// <summary>Returns the hash code for this string.</summary> /// <returns>A 32-bit signed integer hash code.</returns> /// <filterpriority>2</filterpriority> [ReliabilityContract(Consistency.WillNotCorruptState, Cer.MayFail)] public override unsafe int GetHashCode() { fixed (char* text1 = ((char*) this)) { char* chPtr1 = text1; int num1 = 0x15051505; int num2 = num1; int* numPtr1 = (int*) chPtr1; for (int num3 = this.Length; num3 > 0; num3 -= 4) { num1 = (((num1 << 5) + num1) + (num1 >> 0x1b)) ^ numPtr1[0]; if (num3 <= 2) { break; } num2 = (((num2 << 5) + num2) + (num2 >> 0x1b)) ^ numPtr1[1]; numPtr1 += 2; } return (num1 + (num2 * 0x5d588b65)); } } A> GetHashCode algorithm is? A> --- WBR, Michael Nemtsev :: blog: http://spaces.msn.com/laflour "At times one remains faithful to a cause only because its opponents do not cease to be insipid." (c) Friedrich Nietzsche
Do keep in mind that this algorithm can be overridden (and is
overridden) for a large number of classes in the library. There is no such thing as *the* hashcode algo. Jesse [quoted text, click to view] > Use Reflector to get algorithm
> > Code below from the .net 2.0 (have no 1.1 nearby) > /// <summary>Returns the hash code for this string.</summary> > /// <returns>A 32-bit signed integer hash code.</returns> > /// <filterpriority>2</filterpriority> > [ReliabilityContract(Consistency.WillNotCorruptState, Cer.MayFail)] > public override unsafe int GetHashCode() > { > fixed (char* text1 = ((char*) this)) > { > char* chPtr1 = text1; > int num1 = 0x15051505; > int num2 = num1; > int* numPtr1 = (int*) chPtr1; > for (int num3 = this.Length; num3 > 0; num3 -= 4) > { > num1 = (((num1 << 5) + num1) + (num1 >> 0x1b)) ^ > numPtr1[0]; > if (num3 <= 2) > { > break; > } > num2 = (((num2 << 5) + num2) + (num2 >> 0x1b)) ^ > numPtr1[1]; > numPtr1 += 2; > } > return (num1 + (num2 * 0x5d588b65)); > }
Thanks Michael.
I found that code in .NET 2.0 using Reflector, but when I try with .NET 1.1, I only get the method signature. IDLASM also doesn't have any code for 1.1...just says GetHashCode a managed internalcall. Any idea if its possible to get code or even IL for that? [quoted text, click to view] "Michael Nemtsev" wrote:
> Hello ALV, > > Use Reflector to get algorithm > > Code below from the .net 2.0 (have no 1.1 nearby) > /// <summary>Returns the hash code for this string.</summary> > /// <returns>A 32-bit signed integer hash code.</returns> > /// <filterpriority>2</filterpriority> > [ReliabilityContract(Consistency.WillNotCorruptState, Cer.MayFail)] > public override unsafe int GetHashCode() > { > fixed (char* text1 = ((char*) this)) > { > char* chPtr1 = text1; > int num1 = 0x15051505; > int num2 = num1; > int* numPtr1 = (int*) chPtr1; > for (int num3 = this.Length; num3 > 0; num3 -= 4) > { > num1 = (((num1 << 5) + num1) + (num1 >> 0x1b)) ^ numPtr1[0]; > if (num3 <= 2) > { > break; > } > num2 = (((num2 << 5) + num2) + (num2 >> 0x1b)) ^ numPtr1[1]; > numPtr1 += 2; > } > return (num1 + (num2 * 0x5d588b65)); > } > } > > > > A> GetHashCode algorithm is? > A> > --- > WBR, > Michael Nemtsev :: blog: http://spaces.msn.com/laflour > > "At times one remains faithful to a cause only because its opponents do not > cease to be insipid." (c) Friedrich Nietzsche > >
Thanks Jon...that explains why I get different numbers when generating hashes
outside of .NET. I thought the 2.0 algorithm had changed. [quoted text, click to view] "Jon Skeet [C# MVP]" wrote:
> ALV <ALV@discussions.microsoft.com> wrote: > > Within a native C++ app , I need to be able to generate a hash for a given > > string that matches the hash that the same string returns from the .NET 1.1 > > String.GetHashCode(). > > Michael has replied with the algorithm, but it should be stressed that > you *should not* rely on a hashcode being valid outside the environment > it was originally generated in. Hashcodes as given by GetHashCode are > meant to be temporary indications of potential equality. They should > *not* be persisted (which is presumably what has happened here) unless > you have clear documentation saying that this is valid. > > -- > Jon Skeet - <skeet@pobox.com> > http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet > If replying to the group, please do not mail me too
[quoted text, click to view]
ALV <ALV@discussions.microsoft.com> wrote: > Within a native C++ app , I need to be able to generate a hash for a given > string that matches the hash that the same string returns from the .NET 1.1 > String.GetHashCode(). Michael has replied with the algorithm, but it should be stressed that you *should not* rely on a hashcode being valid outside the environment it was originally generated in. Hashcodes as given by GetHashCode are meant to be temporary indications of potential equality. They should *not* be persisted (which is presumably what has happened here) unless you have clear documentation saying that this is valid. -- Jon Skeet - <skeet@pobox.com> http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet
Hello ALV,
U hardly get them both the same, and there is no reason to look at .net realization. Everything depends on you data. Hash algorithm should be tuned to your specific data to get the most rage of data distribution I'd recomend to read Donald E. Knuth books about it, smth like "golden cut set of data distribution" and etc. A> Thanks Jon...that explains why I get different numbers when A> generating hashes outside of .NET. I thought the 2.0 algorithm had A> changed. A> [quoted text, click to view] A> "Jon Skeet [C# MVP]" wrote: ---A> >> ALV <ALV@discussions.microsoft.com> wrote: >> >>> Within a native C++ app , I need to be able to generate a hash for a >>> given string that matches the hash that the same string returns from >>> the .NET 1.1 String.GetHashCode(). >>> >> Michael has replied with the algorithm, but it should be stressed >> that you *should not* rely on a hashcode being valid outside the >> environment it was originally generated in. Hashcodes as given by >> GetHashCode are meant to be temporary indications of potential >> equality. They should *not* be persisted (which is presumably what >> has happened here) unless you have clear documentation saying that >> this is valid. >> >> -- >> Jon Skeet - <skeet@pobox.com> >> http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet >> If replying to the group, please do not mail me too WBR, Michael Nemtsev :: blog: http://spaces.msn.com/laflour "At times one remains faithful to a cause only because its opponents do not cease to be insipid." (c) Friedrich Nietzsch
[quoted text, click to view]
ALV <ALV@discussions.microsoft.com> wrote: > Thanks Jon...that explains why I get different numbers when generating hashes > outside of .NET. I thought the 2.0 algorithm had changed. It *has* changed in .NET 2.0 - and it may well change again. Further, it shouldn't break anything if the runtime decided to take a random number when it started, and added that to the result of every call to String.GetHashCode: the value is crucial *within* that run of an application, but shouldn't be taken to be useful for different runs, even with the same framework version. -- Jon Skeet - <skeet@pobox.com> http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet
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